gastester professional
Contents
1. The metal pipe is for insertion into the exhaust pipe and is retained in position by the metal springs which press against the INSIDE of the exhaust pipe Gunson Eezibleed 2 Co Measurement 1 PREPARATIONS BEFORE USE Any service maintenance such as air filter renewal tappet adjustment carburettor maintenance ignition maintenance including ignition timing should be carried out before setting the carburettor or fuel injection mixture adjustment Petrol mixture setting should be the FINAL ADJUSTMENT in any engine tuning work Carbon monoxide is an EXTREMELY POISONOUS gas ANY work on the car with the engine running should therefore ALWAYS be carried out INTHE OPEN AIR The user should take care NOT TO BREATHE IN exhaust gas when using Gastester near the exhaust pipe with the engine running The car should be thoroughly warm before the tests begin It is not enough to leave the car to warm while parked The car should be taken for a drive and the tests not commenced until water temperature engine and exhaust system are thoroughly heated and are at normal running temperature If a spare battery is to be used the instrument may usefully be warmed up during this period See section 3 8 for COMMON EARTH CONNECTION Study the workshop manual for the particular car or consult the information given later in this booklet to identify the correct adjustment screws that control the mixture strength and the idle speed Identify the direction2. LT terminal of the ignition coil If the low tension terminals are not clearly marked determine the correct one by trial and error as NO damage will occur if this connection is made to the terminal However it is important NOT to try to connect the BLUE lead to the High Tension output of the coil ie the spark plug lead connection as this would damage the internal circuitry of Gastester Professional which is NOT protected against spark voltages d Ensure that all leads are clear of moving parts and that Gastester Professional is in a safe place Start the engine and read the DW ELL on the display in either PERCENT or DEGREES For dwell measurement on other circuits remember that the display will indicate the relative period that NO VOLTAGE is present at the position where the blue lead is connected Dwell is therefore correctly displayed when the earth lead of a coil or injector is sensed as this has a voltage present when the earth is open circuit and none when the circuit is closed This does not apply when the SUPPLY lead is switched Also for positive earth vehicles read the meter backwards For example an indicated dwell of 40E on a 4 cylinder OE to 90E scale is actually 50E 3 PETROL INJECTION TESTS These tests can only be made on cars which have the modern pulsed or intermittent petrol injection system Systems of this type include the following Bosch L LE LH Jetronic Bosch Motronic Lucas Weber VAG Rover Nissan Toyota H
3. electrical voltage applied to a solenoid incorporated in the injector Each injector has an electrical connector with two pins One of these is generally held at live 12 Volt and the other carries the signal to open the injector ie it is connected to earth in a series of timed pulses To check the operation of a petrol injection svstem the following procedure should be used a Set the FUNCTION switch to position DWELL percent b Connect the BLACK clip to the car battery NEGATIVE terminal indicated by neg or black Connect the RED clip to the car battery POSITIVE terminal indicated by pos or red c Connect the BLUE clip to the injector to be tested Injectors generally have a connector with two terminals The signal lead if not indicated in the workshop manual can be found by trial end error since the BLUE lead has very high impedance and no harm will come from making the incorrect connection initially If an in line adaptor connector is unavailable a suitable connection can usually be made by trapping a fine thread of wire such as fuse wire in PICKUP LEAD d Ensure that all leads are clear of moving parts and that GASTESTER PROFESSIONAL is in a safe place and start the engine e The instrument should now be indicating the DW ELL of the particular injector to which it is connected Read the dwell using the percent scale ie the percentage of time that the injector is open It will be noted that the
4. CALIBRATION in air slight drift will occur during extended operation Good stability should be obtained over a period of five minutes or more A variation of for example 0 5 CO at 2 0 CO is not uncommon on an engine which is in good working order Gastester gives errors or slow no response to mixture changes Remedy Check for WATER IN THE PROBE PIPE AND ADEQUATE PROBE INSERTION minimum 8 inches 20 cm If a baffled silencer with no tailpipe is fitted as on some motorcycles temporary restriction of the exhaust outlet or temporary fitting of a tailpipe extension may be the only way to achieve acceptable results NOTE Inuse the pipe from the exhaust probe should preferably slope down continuously to the Pulse Pump Water Trap so that water runs down and may be automatically expelled from the drain pipe OPERATION OF THE PULSE PUMP IS CLEARLY AUDIBLE as the internal diaphragm vibrates with pulsations from the exhaust If response is obtained at higher than idle speeds only Pulse Pump may need replacement Alternatively twist the pump cap on the body to re seat the diaphragm If the pump is working the vehicle mixture adjustment may be ineffective Gastester Professional cannot be set to the Calibration Condition in air after warm up Remedy First check that the unit is switched correctly to CO RANGE and is used in a horizontal position the unit will not operate correctly if instrument is significantly inclined or if the instrument angle
5. SHORTINGA WIRE REMEMBERTO KEEP HANDS ETC WELL CLEAR OFTHE OTHER SHORTING WIRES EMERGING FROM THE DISTRIBUTOR CAP AS THE HT MAV ARC APPROXIMATELY 10MM NEARLY 1 2 INCH 5 Compare the rpm readings for each cylinder Readings should be within 50 rpm of each other if all cylinders are producing equal power Note a poor cylinder will show LESS OF A DROP in rpm and shorting a cylinder which is doing no work will result in NO speed change 4 Dwell Meter 1 GENERAL INFORMATION The dwell function is used for observation of Electronic Ignition and Fuel Injection system Operation and the setting up of contact breaker points Scales for dwell are calibrated in PERCENT and ANGLE IN DEGREES E Dwell PERCENT is the percentage time that current flows in the ignition coil or the injector is open Dwell ANGLE is the degrees of distributor cam rotation during which current flows in the ignition coil Either of the two alternative methods of specification degrees or percent may be used in vehicle manuals For correct degrees measurement the cylinder switch must be set appropriately as dwell is on a OE 90E scale for 4 cylinder engines or OE 60E degrees for a 6 cylinder engine Dwell percent is ALWAYS on a 0 to 100 scale If the dwell period is too small then the current in the ignition coil primary winding does not have time to build to the full value before another spark is demanded which results in a weak spark or no spark at high engine spe
6. TACHOMETER DWELL amp DISTRIBUTORLESS IGNITION 1 Conversions for other types of engine Gastester Professional can be used directly with 2 4 5 and 6 cylinder conventional engines by simply using the CYLINDERS switch set to the appropriate number of cylinders and reading the RPM or DW ELL ANGLE directly from the display Conventional meaning 4 stroke engines with a single set of points electronic trigger and not wasted spark For other engines it is necessary to multiply or divide the reading shown on the scale In most cases the multiplication or division is 2 and can be done by mental arithmetic The circuits of Gastester Professional measure RPM by measuring the rate of ignition pulses ie sparks in the low tension LT winding of the ignition coil The assumption is 1 impulse ie 1 opening of the points or one spark per 2 revolutions of the engine per cylinder ie correspon ding to the 4 stroke combustion cycle There are 4 positions of the Function switch correspon ding to 2 4 5 and 6 cylinders and therefore Gastester Professional assumes 2 Cylinder setting 2 impulses per 2 revolutions 4 Cylinder setting 4 impulses per 2 revolutions 5 Cylinder setting 5 impulses per 2 revolutions 6 Cylinder setting 6 impulses per 2 revolutions For engines with other numbers of cylinders the scale reading can be readily calculated For instance A SINGLE CYLINDER 4 STROKE ENGINE has one spark per 2 revolutions Gastester P
7. but extremely poisonous gas that is present in the exhaust gas of petrol engined vehicles The amount of carbon monoxide in the exhaust gas is an accurate indicator of the air fuel mixture strength being supplied to the engine and for this reason motor manufacturers use the measurement of carbon monoxide in the engine exhaust as the recommended method for setting the air fuel mixture strength on carburettors and fuel injection svstems T he recommended percentage of carbon monoxide in the exhaust at engine idle i e tickover speed is usually specified in the engine maintenance handbook for each vehicle Manufacturers typically specify a CO level somewhere within the range 0 5 to 3 5 by volume and often give an upper and lower limit for the recommended setting for example a manufacturer may specify 0 5 to 1 5 CO Alternatively the data may be given in the for 2 5 CO which means between 1 5 and 2 5 Less commonly and less exactly a manufacturer may simply specify a maximum limit e g below 3 5 CO Carbon monoxide only amounts to a relatively small percentage of the total volume of exhaust gas The bulk of exhaust gas comprises nitrogen N2 carbon dioxide CO 2 water vapour H20 Hydrogen H 2 is also present particularly in association with carbon monoxide Oxvgen O 2 can be present either due to a weak mixture or due to engine misfiring Very small amounts of other substances are also present in exhaust gas such as unburnt or p
8. but the exhaust probe should be removed beforehand VEHICLE REPAIR ISADVISED see Appendix 2 4 If the exhaust pipe has a curved inlet it may be necessary to slightly bend the metal exhaust probe to give better fit This should be done very carefully using slight bends in several places rather than a single big bend in order not to kink the pipe FULL INSERTION IS ESSENTIAL FOR ACCURATE READINGS See section 6 MAINTENANCE andAPPENDIX 2 5 Engine fuel systems are usually designed so that the mixture automatically becomes weaker at speeds above idle except under rapid acceleration when the mixture is enriched see also Appendix 1 Gastester is designed to work at engine tick over speeds however it will also give a reliable reading at higher engine speeds VIOLENT FULLTHROTTLE ACCELERATIONTO HIGH ENGINE SPEED SHOULD BE AVOIDED WHILE THE PROBE IS IN THE EXHAUST PIPE AS THE PULSE PUMP DIAPHRAGMAND PROBE PIPE MAY SUFFER DAMAGE IN EXTREME CIR CUMSTANCES To test mixture weakening at higher RPM increase the engine speed in increments of approximately 300 RPM to 400 RPM up to a maximum of 2500 rpm observing the reading between each adjustment Remember that the instrument may take 15 seconds to respond to a particular adjustment The CO level should fall progressively and stay low during a gradual increase in speed The mixture enrichment for acceleration accelerator pump air valve damper can be tested by rapid opening and immediate release o
9. is changed after calibration Ensure that the unit is connected to a car battery nb a 12v dry cell battery or a faulty car battery can not provide enough current and are unsatisfactory Ensure that the unit is correctly warmed up allow at least 10 minutes Ensure that the unit is being calibrated to the 2 CO condition NOT at zero Ensure that the probe is in air not in the exhaust pipe If these checks do not resolve the problem it is possible that the instrument has drifted generally due to collector box contamination or damage due to impact the instrument is more susceptible to damage when warm and in use The unit should be returned to Gunson for service For further details of services and charges or any other enquiries please send a Stamped Addressed Envelope to Service Department Gunson Ltd 21 Gunson Gastester Professional 7 3 MULTIPLE CARBURETTORS W here two separate carburettors are fitted not to be confused with a twin choke carburettor two extra complications arise Firstiv the air flow through the carburettors must be accuratelv balanced before anv mixture setting can be undertaken This can be done using Gunson s Carbalancer or less accuratelv with a tube to listen to the air intake hiss Secondly there will be separate mixture adjustments which must be synchronised In the unlikely event that cylinders fed by each carburettor have totally separate exhaust CO can be checked in each exhaust to set the respectiv
10. minute then taking a measurement with the headlamps off 2 INSTRUCTIONS FORVOLTAGE MEASUREMENT a Connect the RED lead to battery and the BLACK lead to battery b Connect the blue lead to the battery to read battery voltage and refer to the following section for information on values Figure 4 MEASUREMENT OF BATTERY CHARGING and CRANKING VOLTAGE ETC POWER LEADS PICKUP LEAD 3 INSTRUCTIONS ALTERNATORAND REGULATORTEST 16 Gunson Gastester Professional Before carrying out this test ensure that the battery has been recently fully charged a Connect RED lead to battery BLACK lead to battery Connect the BLUE lead to the coil negative so that RPM may be set b Ensure that leads are clear of moving parts Start engine and set engine RPM to a speed of approximately 2000 RPM or a figure recommended in manufacturers data c Carefully move the BLUE lead to the battery positive connection d NO LOADTEST With all electrical loads off observe the meter reading e LOADTEST Turn on as many electrical loads as possible e g headlamps rear screen heater windscreen wipers heater fan etc Vary the engine speed The meter reading should remain within specification at all engine speeds except slightly above idle when it may fall FURTHER NOTES Battery voltage New fully charged 12 6V to 13 4V inc surface charge Old fully charged 12 2V to 13 0V inc surface charge Typical alte
11. the exhaust from the instrument This period in air with power on cleans the sensor before storage and also allows a check to ensure the display returns close to the 2 setting indicating that there has been little drift in calibration NOTE A final reading of 1 8 in air for example would suggest that the last exhaust measurement was approx 0 2 lower than the displayed level While this is perfectly acceptable when setting to approx 3 to ensure that a vehicle passes a 4 5 maximum legal requirement it does represent a more significant error if setting to a manufacturers recommended 0 5 CO On occasions it may be necessary to repeat a test if calibration drift is excessive drift is reduced by keeping test duration short and allowing a long warm up Gunson Eezibleed 3 FURTHER INFORMATION It should be noted that an engine even in good overall condition will show a fluctuation in idle CO over a period of time of typically 0 5 Bearing in mind this fluctuation and also errors and drift in the instrument the user should aim to set the average CO reading to be midway between the limits set by the manufacturer or at a reasonable margin below the prescribed legal limit If the CO level is correct HC levels should also be low if general engine condition adjustment is reasonable See also Appendix 7 2 Periodically during the tests examine the lowest point of the transparent plastic pipe to see if it contains water to a degree that might imped
12. to turn the screws to achieve the desired effect i e mixture richer or weaker idle speed faster or Sower If in doubt make a note of the initial position of the adjustments before commencing work so that in case of difficulty or if the wrong adjustment is changed the setting can be restored to its original position Check the manual for the correct CO and IDLE RPM values Have to hand the correct tools for making the necessary adjustments 2 2 INSTRUCTIONS FOR USE a Ensure that the car is thoroughly warm as mentioned above that it is parked in a convenient position in the open air with the handbrake applied NOTE THE INSTRUMENT SHOULD NOT BE PLACED DIRECTLY IN THE EXHAUST STREAM CLEAN AIR IS REQUIRED IN THE REFERENCE CELL FORACCURATE READINGS NOTE Bright sunlight on the instrument will make visibility of the led display difficult b Place the Gastester Professional on a convenient flat surface close to the vehicle s exhaust pipe outlet Switch off the engine temporarily while making connections Connect the RED and BLACK clips to the vehicle s 12 V battery RED to BLACK to and the BLUE pickup lead to the COIL NEGATIVE terminal to obtain RPM readings THE PROBE SHOULD BE FITTEDTO THE INSTRUMENT BUT DO NOT INSERT THE EXHAUST PROBE INTO THE EXHAUST PIPE AT THIS STAGE c Restart the engine and allow a MINIMUM PERIOD OF 8 MINUTES with the instrument 8 Gunson Eezibleed probe in air Set the calibration control to ac
13. E VEHICLE EXHAUST PIPE to a minimum of 3 4 of its length i e 8 or 20cm In order for the automatic water drain to function the probe pipe should fall continuously from the exhaust end to the inlet end to allow water droplets to run down Otherwise the water will collect at the lowest point and will have to be drained manually f Wait for a period of 15 seconds for the meter to respond and a further 1 minute to stabilise the reading may overshoot before returning to a steady value particularly during the initial measurement MAKE A NOTE OF THE READING AND OBSERVE THE DISPLAY FORA FURTHER ONE OR TWO MINUTES TO ENSURE THAT THE READING IS INDEED STEADY AND WITHIN TOLERANCE FORTHE VEHICLE CONCERNED If the reading is not between the manufacturer s recommended maximum and minimum or is not below that specified as a legal requirement then adjustment of the carburettor or fuel injection system will be required g If adjustment is required make a small alteration to the mixture screw and correct the idle speed by adjusting the idle speed screw or throttle bypass screw if fitted see figure 9 amp 12 Do this repeatedly in small increments under these conditions the reading should stabilise in less than one minute at each mixture setting h When the test is complete REMOVETHE EXHAUST PROBE PIPE and switch off the engine Allow a period of at least 5 minutes or at least 10 minutes in still air conditions with little breeze for air to purge
14. Gunson PROFESSIONAL Exhaust CO Gas amp Engine Analyser PART NO G4121 HANDBOOK Gunson Gastester Professional Gunson Gastester Professional SAFETV WARNING Engine exhaust gas is VERY POISONOUS Do not carry out work on a car indoors or in a confined space with the engine running Ensure that the car is outdoors and with free ventilation of fresh air Avoid breathing exhaust gas while using Gastester Professional in the region of the exhaust pipe DO NOT work on an engine while wearing loose clothing or with long hair not tied up Keep hands clothing instrument leads and connectors in a safe position clear of moving parts fan rotating pulleys and fanbelt clear of excessively hot parts exhaust manifold exhaust pipe and HT voltages spark plugs and any ignition parts which may produce a high tension spark HT VOLTAGES from ignition systems are DANGEROUS Though unlikely in themselves to cause permanent injury to a HEALTHY person they are likely to cause involuntary movement which IS dangerous when in proximity to an engine compartment WARNING Take care not to short circuit connect directly together vehicle powered leads and earthed leads metal note including leads switched between these voltages High currents may result in damaged or burnt components IMPORTANT OPERATING NOTES This instrument should be allowed to warm up for an absolute minimum of 10 minutes a reasonably accurate spot check of CO level is th
15. S FOR USE a Set the FUNCTION switch to position RPM low or RPM x 1000 high depending on the range of RPM to be measured b Set the Cylinders switch to the number of cylinders of the engine c Connect the BLACK lead to the car battery terminal and the RED lead to the car battery terminal ll Gunson Gastester Professional d Connect the BLUE lead to the low tension LT terminal of the ignition coil If the low tension terminals are not clearly marked determine the correct one by trial and error as NO damage will occur if this connection is made to the terminal However it is important NOT totry to connect the BLUE lead to the HighTension output of the coil ie the spark plug lead connection as this would damage the internal circuitry of Gastester Professional which is not protected against spark voltages Figure 2 TACHOMETER amp DWELL CONNECTIONS POWER LEADS e Ensure that all leads are clear of moving parts and that Gastester Professional is in a safe place Start the engine and read the engine RPM on the display remembering to multiply the scale reading by 1000 if RPM high has been selected Gastester Professional can be used directly with 2 4 5 and 6 cylinder conventional engines by simply using the CYLINDERS switch set to the appropriate number of cylinders and reading the RPM or DW ELL ANGLE directly from the display Conventional meaning 4 stroke engines with a single set of
16. artially burnt fuel generally referred to as hydrocarbons and also some oxides of nitrogen The way that the composition of exhaust gas varies with petrol air mixture strength is illustrated in Figure 5 Idle CO setting range for modern vehicles A typical recommended setting for a particular car the width of the band shows the upper and lower limits 11 1 12 1 13 1 14 1 15 1 16 1 17 1 RICH AIR FUEL RATIO WEAK It can be seen from Figure 5 that at a particular air fuel mixture ratio somewhere near 14 7 1 for petrol engines the amount of oxygen present in the air that is entering the engine is exactly that required to completely burn all the petrol to carbon dioxide and water There is therefore very little carbon monoxide in the exhaust and no free oxygen This particular ratio of air and petrol is known as the stoichiometric ratio At this ratio the percentage of carbon dioxide in the exhaust is at a maximum and the percentage of carbon monoxide is very low In mixtures richer than the stoichiometric ratio i e more fuel or less air there is insufficient oxygen in the air to burn all the carbon in the fuel completely to carbon dioxide Some carbon therefore exists in the form of carbon monoxide and the richer the mixture the more carbon monoxide and the less carbon dioxide there is in the exhaust It can be seen from Figure 5 that 19 Gunson Gastester Professional motor manufacturers generally specify a mixture strengt
17. ch requires a special tool for easy adjustment It is screwed up to weaken clockwise looking from underneath Other types adjustable needle are plugged underneath and have a slot in the air valve piston guide rod Remove damper and look inside to check for this The slot is across the smallest tube which is visible An adjusting tool is also required here Figure 11 STROMBERG CDSEV NEEDLE ADJUSTMENT BV REMOVING DAMPER ALTERNATIVE VARIETV L WITH SLOT HEX KEY MIXTURE ADJUSTMENT ADJUSTABLE JET VERSIONS 5 TWIN VENTURI CARBURETTORS TWIN CHOKE PROGRESSION TYPE On this type two venturis are incorporated in the same casting One throttle plate opens before the other observe while operating the throttle linkage At low speeds and for idle mixture adjustment this type can be considered similar to the single choke type all adjustments being carried out on the barrel which opens first The Pierburg 2E3 shown in figure 7 has a diaphragm operated second barrel and the idle adjustment is by the throttle stop screw and idle mixture screw shown On the G M Varajet carburettor shown in Figure 12 the secondary barrel is of variable venturi design This has no bearing on the idle setting which is of the by pass type Idle speed is adjusted 26 Gunson Gastester Professional on the throttle bv pass screw 6 TWIN VENTURI CARBURETTOR SIMULTANEOUSTVPE On this type the two venturis are incorporated in the same casting an
18. d both throttle plates operate at the same time There is usually no need to balance the air flows through the two barrels they are often linked by a single throttle spindle Balancing of the two mixture screws is obtained by setting to the same number of turns open Figure 13 G MVARAJET IGNITION VACUUM ADVANCE PIPE Figure 13 K JETRONIC IDLE MIXTURE CO ADJUSTMENT THROTTLE BYPASS IDLE MIXTURE IDLE SPEED SCREW CO SCREW LUCAS LH 7 PETROL INJECTION SYSTEMS Modern fuel injection systems can be either of the continuous type e g Bosch K amp KE Jetronic or intermittent type e g Bosch L LE LE2 Jetronic Motronic Lucas LH etc Adjustment screws are provided for idle mixture CO In some versions idle speed is not mechanically adjustable The manufacturer s instructions should be carefully followed for particular models The illustra tions below show examples of types of adjustments Some older types of system e g Triumph PI used separate throttle plates per cylinder and a common idle mixture screw W ith this type it is essential to obtain an accurate balance through 27 Gunson Gastester Professional each throttle plate before anv mixture setting is undertaken This can be done using Carbalancer or Colortune as mentioned in APPENDIX 3 W here separate control screws are provided for each cylinder adjustment should remain synchronised by using the same turns for each screw during adjustments 7 5
19. e carburettor When the exhaust is common to all cylinders another method must be used One method is to count the turns of the mixture adjusting screws from the fully closed position or jet flush with the bridge for variable venturi types and then ensure that the screws are kept to the same number of turns throughout adjustment An alternative and better method is to use Gunson s C olortune to set the mixture strengths equal at some point then to ensure that the screws are turned the same amount during subsequent adjustments 7 4 CARBURETTOR ADJUSTMENTS 1 GENERAL INFORMATION There are literally hundreds of different types of carburettor in use today and finding the appropriate screws that control idle mixture strength and idle speed can pose quite a problem Wherever possible the user is advised to consult a detailed workshop manual for the particular car but the following notes are provided for use when such information is not available Firstly it should be mentioned that it is a legal requirement that all carburettors have either a method of sealing the adjusting screws or require the use of a special tool to enable adjustments to be made In some ways this has been a retrograde step it may stop tinkering by an unskilled owner but wear of the various parts takes place during the life of the car and mixture adjustment is frequently ignored until it becomes troublesome in terms of starting performance or economy Seals are usually t
20. e the flow of gas and if it does remove the pipe at the instrument gas inlet end and clear the pipe by allowing the water to drain out then reconnect the pipe and carry on with the tests If the transparent pipe falls continuously from the exhaust to the pump the automatic drain should operate and keep the pipe clear of water NOTE Operation of the pulse pump will usually be audible as the pulsations in the exhaust cause the internal diaphragm to vibrate If the instrument ceases to respond to changes in mixture set ting or the sound from the pulse pump becomes irregular check the sample pipe for collected water SEE ALSO SECTION 6 MAINTENANCE The calibration of the instrument may be checked at any time Simply remove the exhaust probe and wait at least five minutes or at least ten minutes in still air conditions with little breeze for the exhaust gas to disperse from the collector box If necessary the calibration may then be adjusted using the calibration control knob The user is advised to periodically check the calibration of the instrument during particularly extended tests Some motor car engines will not readily tick over at idle speeds for long periods The speed may become erratic and engine misfiring may occur W ith the prolonged testing of such engines it may be necessary to occasionally purge the engine by for instance increasing the speed to 2000 rpm 3000 rpm for 15 seconds This may be done at any time during the tests
21. ed The car may start and idle OK but the user may notice reduced performance or misfire at high RPM If the dwell period is too great failure of ignition components may result With contact breaker systems with points other problems will arise such as engine misfire It is for these reasons that modern electronic systems have variable dwell of for example 10 at low rpm and 50 at high rpm Ignition systems with contact points generally have a fixed dwell which is constant no matter how engine RPM is varied In practice there may be some small variation of dwell with engine speed which may be ignored The points gap should be set to the dwell recommended by the vehicle manufacturer Note If considerable distributor shaft wear has taken place points gap may not then be as prescribed INCREASING THE POINTS GAP REDUCESTHE DWELL REDUCING THE POINTS GAP INCREASESTHE DWELL Gunson Gastester Professional 2 INSTRUCTIONS FOR DWELL MEASUREMENT a Set the FUNCTION switch to position DWELL PERCENT or alternatively DWELL ANGLE E depending on the range to be measured b Set the Cylinders switch to the number of cylinders of the engine if using the DW ELL ANGLE range b See TACHOMETER amp DWELL CONNECTIONS Fig 2 in the previous section Connect the BLACK lead to the car battery terminal and the RED lead to the car battery terminal c For measurement of ignition system dwell connect the BLUE lead to the low tension
22. en possible However to maintain accuracy during more prolonged testing adjustment allow a longer warm up e g 20 30 minutes so that setting drift is reduced to a minimum and check the 2 setting in air 10 minutes after probe removal see main instructions Warm up the instrument in the same location position as it is to be used IMPORTANT DO NOT DISTURB THE INSTRUMENT POSITION AFTER SETTINGTO 2 0 The instrument displays two decimal places on the CO range as a result of the high resolution display The last decimal place is insignificant and when setting to 2 in air the user should not be concerned if 2 00 exactly can not be obtained SENSOR LIFE To prolong sensor life allow a period of 10 minutes in air power on after use and avoid excessively rich mixtures With frequent heavy commercial use the sensor may become contaminated within less than one year Note M O T class infra red analysers with extensive filtration require calibration up to four times annually Increasing difficulty in obtaining 2 0 setting in air with the adjustment becoming offset is one clear indication of the need for sensor replacement INSTRUMENT CIRCUIT PROTECTION Gastester Professional circuitry is fully protected against incorrect connection and can be subjected to car battery voltages and the instantaneous peaks found in ignition low tension injection and control systems T he high impedance of the BLUE pickup lead ensures that it can not damage the ci
23. f the accelerator Opening to half throttle should be sufficient Within a few seconds of this operation the Gastester CO indication should increase 10 Gunson Eezibleed before returning to its previous setting The degree of increase will varv according to how this procedure is carried out and also with the tvpe of fuel svstem A fixed choke carburettor with accelerator pump will usually give a more pronounced increase than a variable choke carburettor or fuel injection system Use only a 12 volt car battery in good condition as power supply Smaller batteries or a faulty or flat car battery may not be able to supply adequate current to the instrument Gastester Professional draws about 0 8 amps resulting in errors in use and difficulty in calibration If the vehicle has a 6v or 24v battery use an external battery such as the battery of a nearby car If a separate battery is used ie not the battery fitted to the car it is necessary to connect the negative terminal of the vehicle battery to the negative of the power battery to give a common earth before connecting the blue lead This will enable the rpm voltage and dwell ranges to function 3 Tachometer LGENERAL INFORMATION Two ranges are provided RPM low measures RPM directly in the range 0 to 1999 RPM and is intended for tests at or around idle speed RPM high measures RPM in the range 0 to 19 999 and covers the whole operating speed range of all engines RPM high is disp
24. h at idle that is slightly richer than the stoichiometric ratio Under some conditions such as starting an engine from cold or during acceleration very much richer mixtures are used In mixtures weaker than the stoichiometric ratio i e less fuel or more air there is more oxygen in the air than required for complete combustion of the petrol and the surplus oxygen appears in the exhaust gas The level of carbon monoxide is very low since virtually all the carbon in the petrol is completely burnt to carbon dioxide There is however a smaller percentage of carbon dioxide present in the exhaust than at the stoichiometric ratio of air and fuel simply due to the diluting effect of the extra air passing through the engine Engines are commonly designed to run with such weak mixtures under light load driving conditions though not at idle An engine will run indeed run quite well at mixtures that are richer or weaker than those specified by the motor manufacturer However at settings richer than the manufacturer recommends there is a loss in economy and at very rich settings typically 8 to 10 C O the onset of poor running occurs characterised by the particular engine sound that is known as hunting At settings weaker than the manufacturer recommends there is poor engine performance and flat spots and at very weak settings typically 2 to 4 oxygen the engine will not run at all Note that at very weak settings it is inappropriate to spea
25. hieve 2 on the CO range and observe the display for A FURTHER 2 MINUTES MINIMUM to ensure that the reading has stabilised IMPORTANT IF IT HAS NOT STABILISED ALLOW A FURTHER PERIOD BEFORE ATTEMPTING TOMEASURE EXHAUST CO LEVEL ALSO SEE PAGE 2 IMPORTANT OPERATING NOTES During the warm up period other ranges will give accurate readings and it is therefore useful to check and adjust engine IDLE RPM d Switch to the CO range with the probe in air DO NOT INSERT THE EXHAUST PROBE INTO THE EXHAUST PIPE AT THIS STAGE Use the rotary calibration control to carefully reset to the CALIBRATE reading of 2 0 CO The instrument displays two decimal places on the CO range as a result of the high resolution display The last decimal place is insignificant and when setting to 2 in air the user should not be concerned if 2 00 exactly can not be obtained Having set the CALIBRATE condition do not move the instrument or move to a different location during subsequent CO tests NB The CALIBRATE position represents what the instrument should register when the probe is in air It is coincidental that air should measure the same as exhaust gas with 2 CO When the probe is subsequently inserted into the exhaust pipe the display of the instrument may increase or fall from the CALIBRATE condition depending on whether the exhaust has more than or less than 2 CO e Ensure that the engine is set to the IDLE RPM stated by the manufacturer NOW INSERT THE PROBE INTO TH
26. hin metal or plastic plugs which are destroyed on removal and are usually removed using a sharp screwdriver bit or short self tapping screw Other types offer a limited adjustment which can be increased by removal of a cap and some cover seals have a removable centre section allowing access to the adjustment The vehicle manufacturer will invariably recommend that the seals are renewed after adjustment but this is frequently ignored by the service trade or vehicle owner particularly after the service warranty has expired In some countries particularly the USA and Japan this would be an offence 2 IDLE CIRCUITS Carburettor types can be divided into those that have a separate fuel circuit for idle and those without a separate idle circuit Figure 6 shows a typical arrangement of separate idle circuit The mixture is made richer i e CO higher by screwing the screw out 22 Gunson Gastester Professional IGNITION ADVANCE DRILLING IDLE MIXTURE IDLE MIXTURE PROGRESSION CO SCREW HOLE DISCHARGE In such carburettors idle speed can be of the adjustable throttle stop type an example being shown in Figure 7 PIERBURG 2E3 ae Na Se IDLE SPEED SEHEM IDLE MIXTURE SCREW An alternative arrangement of separate idle fuel circuit with idle speed adjustment of the throttle bypass type is shown in Figures 8 and 9 In this type idle speed is controlled by a screw controlling the flow of air and fuel through a bypass cha
27. ines the instrument may also be used on motorcycles and other engines including single cylinder engines with the following proviso a The CO range may NOT be used on TWO STROKE engines and on four stroke motor cycles a suitable exhaust tailpipe fitting is required for full insertion of the probe b For two stroke and four stroke motorcycle type engines see APPENDIX 5 1 for cylinder switch setting for Tachometer and Dwell ranges and APPENDIX 5 5 for other than 12v applications 9 Technical Specification CO FUNCTION Calibrated range 0 10 co indicates uncalibrated to 20 co Accuracy 0 5 co typical throughout the indicated range 0 5 co to 6 5 co BATTERY ALTERNATOR VOLTAGE Indicated 0 20v Accuracy at 12 0 v 0 05 v RPM LOW Indicated 0 1999 rpm Accuracy within 2 of reading plus 1 digit 1 digit 1 rpm RPM HIGH x1000 Indicated 0 19 990 rpm Gunson Gastester Professional Accuracy within 2 of reading plus 1 digit 1 digit 10 rpm DW ELL ANGLE DEGREES Indicated to suit number of cylinders Accuracy within 1 of reading plus 1 digit 1 digit 0 1 degree DWELL PERIOD PERCENT Indicated 0 100 Accuracy within 1 of reading plus 1 digit 1 digit 0 1 percent 10 Warranty This warranty is in addition to the statutory rights of the purchaser The Tool Connection has made every effort to ensure that this product is of the highest quality and value to the customer However The Tool C
28. injector dwell increases only slightly at high RPM but depends largely on the position of the throttle For tests on a stationary vehicle injector dwell will be seen to be very low for all RPM If the throttle is blipped a momentary high increase in injector dwell will be seen while the accelerator is depressed On some cars the injectors cut out on the over run in order to reduce pollution and save fuel With these systems eg some Bosch LE and others the injector dwell will be seen to reduce to zero until the engine speed has reduced to idle when the injectors will resume working Operation of the choke can be seen as an increased reading when cold except on those vehicles where the choke function is achieved via a separate additional injector WARNING TAKE CARE NOT TO SHORT CIRCUIT CONNECT DIRECTLY TOGETHER POWERED AND EARTHED LEADS Including leads switched between these voltages Gastester Professional circuitry is fully protected against incorrect connection and can be subjected to car battery voltages and the instantaneous peaks found in ignition low tension 15 Gunson Gastester Professional injection and control systems T he high impedance of the BLUE pickup lead ensures that it can not damage the circuitry being tested 5 Voltage 0 20 volts dc This range is for measuring battery voltage during charging starting etc and may also be used to indicate terminal voltage of ancillary electrical equipment Because the bl
29. is type gives improved accuracy of fuel metering Replace at 50 000 miles 80 000 km intervals Note the needle housing should not be rotated as the direction of spring loading will be affected Fuel metering needles are manufactured to within 0025mm 0001 and should be handled carefully SU type HIF and Stromberg CDSE types have a temperature compensating device fitted but other SU and Stromberg CD types should be set when the carburettor is warm to the touch but not hot to achieve maximum setting accuracy IDLE ADJUSTMENT The idle speed screw generally acts on the throttle spindle to which the accelerator linkage is connected this will give very fine adjustment of the throttle The mixture screw also affecting mixture at high speeds is located in different positions on different types 25 Gunson Gastester Professional SU TVPE On early versions this is generally a hexagon nut underneath the carburettor and is screwed up to weaken clockwise looking from underneath Other types HSB HD etc have a screw which raises and lowers the jet through a system of levers HIF types have a screw which is located behind removable plug in the right hand side of the carburettor screwing in clockwise enriches the mixture Occasionally adjustment is on the left one left one right on twins CDTYPE On early versions there is generally underneath the carburettor either a large dotted screw or in later types a castellated bush whi
30. k of the CO level since CO reaches a very low level below which it hardly changes for further weakening of the mixture and some other indicator of mixture strength must be used such as oxygen It has already been mentioned that motor manufacturers specify a CO level at a particular engine idle RPM but that the CO level under other engine running conditions will generally be different from this A richer mixture is used when starting the engine from cold a weaker mixture when driving under light power a richer mixture when accelerating etc However the user does not need to be aware of this It is simply necessary to set the mixture strength at idle as specified by the motor manufacturer and the carburettor or fuel injection system then automatically sets the mixture right at other engine conditions Gastester is an exhaust gas analyser that works on the Hot Wire or Thermal Conductivity principle According to this principle the thermal conductivity of exhaust gas varies in proportion to the amount of carbon monoxide present 7 2 Common Problems 1 The car does not drive well with the correct idle mixture setting This is a common complaint On older vehicles the cause is likely to be a fuel system fault which creates a weak mixture just above idle speed Remedy Clean the idle jet and idle air bleed jet on fixed choke carburettors Check for needle jet wear on variable choke carburettors above 40 000 miles These are available as
31. layed in thousands and so the figure displayed needs to be multiplied by 1000 for the correct reading For instance a display reading of 3 25 represents 3 250 RPM The principle of operation of the measuring circuit is to measure the rate of ignition pulses in the low tension LT winding of the ignition coil This instrument is therefore only suitable for coil spark ignition systems but it can equally be used on conventional points and electronic ignition systems since both types of ignition system utilise an ignition coil However it can not be used on magneto or and some capacitive discharge systems that are occasionally usedin racing engines The calibration of the display assumes a 4 stroke engine i e one firing stroke per 2 revolutions of the engine per cylinder and a single ignition distributor shaft The display can be read directly for all such engines which have 2 4 5 or 6 cylinders as set by the cylinders switch For use with other types of engine and ignition system see APPENDIX 7 5 It is acceptable indeed often desirable to switch to RPM measurement while measuring exhaust gas CO In this case the instrument should be placed on the ground at the rear of the car and not moved after it has been calibrated for CO measurement If the instrument is not required for simultaneous CO measurement the it is acceptable to move the instrument closer to the engine bay for RPM measurement if preferred for convenience 2 INSTRUCTION
32. ms Gastester Professional will not give an accurate reading of RPM with a 6 Volt vehicle using that vehicle s battery To use Gastester Professional to measure the RPM of a 6 Volt vehicle connect 29 Gunson Gastester Professional the Red and Black leads to an external 12V batterv remembering to connect a common earth between the vehicle earth and the external batterv and connecting the Blue lead as described previousiv Gastester Professional should not be used on a 24V vehicle using that vehicle s battery To avoid damage to the meter s circuitry an external 12V battery should be used and a common earth connected between the vehicle and external battery as mentioned above 7 6 ALTERNATOR STARTER AND BATTERY TESTING Typical battery voltage during cranking HOT 10 5 to 115 volts engine and environment hot cranking at approx 450 RPM Typical battery voltage during cranking COLD 9 5 to 10 5 volts engine and environment cold cranking at approx 200 RPM When testing the starter motor cranking circuit connect the blue lead to the battery post followed by the battery connector the solenoid connector and if available the starter motor connection Compare these voltages under cranking in each case to detect a component with an excessive drop indicating a fault 8 Specification Gastester Professional is a combined exhaust gas CO analyser tachometer dwellmeter and voltmeter Though primarily intended for multi cylinder car eng
33. nly used on some vintage cars and some motorcycles The ignition coil has a primary winding or low tension which will generally have two visible connections to which are attached a cable of normal insulation thickness 2 5 mm Following the plug leads back from the spark plugs will except DIS systems identify the distributor Another thick lead of plug lead type the king lead will lead from the distributor to the coil On the coil will be two connectors to the primary winding In DIS systems the plug leads go to the coil direct With some cars the coil is covered by cowling or is enclosed within the engine management system In such cases the user should refer to the workshop manual of the car for the location of the coil and in particular to the location of the terminals of the primary winding to which Gastester Professional is connected Some ignition coils are totally enclosed or are virtually inaccessible In these cases the user must examine the circuit diagram of the car to identify a wire or connector that a tachometer or Gastester Professional blue lead can be connected to Where an ignition coil has exposed spade type connections it is easy to connect the crocodile clip of Gastester Professional directly Where an ignition coil has an insulated plug and socket arrangement it may be necessary to improvise a suitable connection such as by trapping a short length of fine wire e g fuse wire between the plug and socket and making
34. nnel and not by varying the position of the throttle plate In such types the idle speed adjustment and idle mixture adjustment are usually located near to each other on the same side of the carburettor On certain types the bypass channel may have its own mixture adjustment shown dotted for example some Solex EEIT carburettors In this Solex twin carburettor the mixture to both barrels is adjusted using the mixture bypass screw the two conventional mixture screws normally remaining unaltered It should be noted that with this type when the bypass screw is used to change the engine speed the mixture is affected also It is therefore important to correct idle speed after each mixture adjustment and to work in small increments of adjustment It should also be noted that when a throttle bypass screw is fitted the throttle stop screw will normally be locked or sealed and in such units the throttle stop screw should not be disturbed Gunson Gastester Professional IGNITION ADVANCE DRILLING ee BYPASS MIXTURE Nr II OCCASSIONAL FITMENT IDLE MIXTURE PROGRESSION IDLE MIXTURE CO SCREW HOLES DISCHARGE Figure 9 SOLEX PDSI l IGNITION _ AA VACUUM x ADVANCE eS PIPE W D ff JI THROTTLE BYPASS IDLE SPEED SCREW IDLE MIXTURE SCREW Carburettors without a separate idle mixture circuit are typified by the SU and CD horizontal variable venturi types Mixture throughout the speed range is governed by a long
35. on should contain the following items Gastester Professional unit Exhaust probe complete with plastic pipe and 2 retaining springs Handbook Dwell data leaflet Features of the product are illustrated in Figure 1 and described below DISPLAY FUNCTION SWITCH CYLINDERS SWITCH CALIBRATE KNOB PULSE PUMP GAS INLET GAS OUTLET GASVENT WATER DRAIN RED amp BLACK LEADS BLUE LEAD EXHAUST PROBE Large 15 mm Light Emitting Diode display showing 3_ digits ie maximum scale reading 1999 minimum scale reading 1999 Over range is indicated by 1 in the LEFT display only and zero by 000 Decimal points are added appropriate to the scale selected Used to select the required function Exhaust CO measurement Voltage Engine RPM high Engine RPM low Dwell degrees Dwell percent For setting the number of cylinders this switch is effective on RPM and DWELL ANGLE ranges Only used in CO measurement for initial calibration of the instrument by setting the display to read 2 0 with the exhaust probe in air This is a non powered pump driven by pressure fluctuations in the exhaust to give a consistent gas flow in the analyser For connection of the exhaust probe Exhaust gas outlet do not restrict Exhaust gas outlet do not restrict At the rear of the instrument Ejects water drained from the exhaust gas These leads provide power from the car battery Pickup used in RPM Dwell and Volts measurements
36. onda Mazda Subaru Suzuki Renix Mitsubishi Isuzu NOT BOSCH K KE JETRONIC NOT TRIUMPH LUCAS PI However it should be cautioned that as this is an area of rapidly advancing technology Gunson are unable to guarantee operation on all intermittent systems Before carrying out tests on a car some understanding is necessary of the principle of operation of the particular petrol injection system being tested This is the user s responsibility to make reference to the technical manual of the particular car being tested In general the following notes apply to most cars One petrol injector is provided for each cylinder and this injects a single squirt of petrol once per engine revolution into the inlet manifold at a point near the inlet valve All injectors 4 for a 4 cylinder car operate at the same instant in time It follows that some injectors are injecting at a time when the inlet valve is not open Some cars have a slightly different system where each injector operates twice per revolution below a particular RPM eg Toyota The engine management system computes the petrol required and opens each injector for a fixed time per revolution The injection pressure with respect to the inlet manifold is constant therefore it follows that the amount of petrol injected per revolution is proportional to the time that the injector is open Injectors are closed by a spring and are opened and held open by an 14 Gunson Gastester Professional
37. onnection can accept no responsibility for consequential damage howsoever caused arising from the use of this product All technical enquiries regarding this product should be made to The Tool Connection Technical Service Department 444 0 1926 818181 Please note that The Tool Connection cannot provide technical information or advice or service data on particular motor vehicles If this product should require service or repair it should be returned to The Tool Connection Kineton Road Southam Warwickshire CV47 ODR England Please give full details of faults requiring attention when sending goods for service or repair Gunson 05 2005 31 Do you need a thingamajig or a whatsit for a doo dah LASER s New Tools Forum e Helps you find the tools you need e Helps us supply the tools you need e Helps others get more information New Tool Forum lasertools co uk If you do tools come and talk tools Distributed by The Tool Connection Ltd Kineton Road T 44 0 1926 815000 T Koo E Southam F 44 0 1926 815888 e CONNECTION Warwickshire info toolconnection co uk CV47 ODR www toolconnection co uk
38. oor cranking i e the engine turning over slowly imply a relatively high resistance in the circuit external to the battery This could be a fault in the starter motor or could be a high voltage drop across a component such as a battery terminal or 17 Gunson Gastester Professional the solenoid or a starter terminal To investigate these possibilities check the voltages at these positions to ensure the starter is receiving almost full batterv voltage If the starter refuses to crank the engine at all then the cause mav be a jammed starter motor in which case the voltage will rapidly fall to approx 9 volts and beyond as approx 450 Amps is drawn typically by a locked starter motor On the other hand the cause may be a break in the starter circuit such asa totally failed starter motor or solenoid in which case the voltage will remain high FURTHER NOTES Take care not to crank the engine for long periods which will result in excessive heating of the starter motor 6 Maintenance PULSE PUMP The pulse pump SHOULD BE AUDIBLE during use at idle rpm as it reacts to pressure fluctuations in the exhaust Response to mixture changes should occur within 15 seconds if sample flow is normal Should correct operation not be achieved check that the probe is being fully inserted in the vehicle tailpipe If faulty operation of the pulse pump is suspected check also that the pump is not filled with water then that the diaphragm is flat and therefo
39. points electronic trigger and not wasted spark For the correct connection to Ford DIS ignition systems and display ranges on other systems refer to APPENDIX 7 5 3 POWER BALANCETEST This is a useful test widely used in the motor trade to detect or confirm the presence of a fault which is affecting one cylinder more than the others Such faults include faulty spark plug poor cylinder compression faulty petrol injector air leak on the inlet manifold affecting one cylinder etc In order to perform this test accurately and without risk of high voltages tracking if plug leads are removed we recommend the following method a Place a thin piece of uninsulated wire under each plug lead connection preferably at the distributor cap leaving a short length exposed b Connect a jumper lead to a reliable earth nearby and the free end to an insulated screw driver This is for shorting the exposed wires to earth in turn and can be handled with safetv as it provides a preferred path to earth c Start the engine the engine should be warm and may need to be set just above normal idle speed eg 1000 rpm 12 Gunson Gastester Professional d Short each spark plug lead in turn to earth using the screwdriver with earth connection to bridge between each of the uninsulated wires and earth and observe the reduced engine rpm Allow a period of approximatelv five seconds per cvlinder with sufficient recoverv time between WHEN
40. r inlet but more than one carburettor is sometimes fitted see Section 8 Twin and Multiple carburettors a throttle plate or butterfly and an air valve or a piston which closes off the air inlet to which is attached a tapered fuel metering needle This needle runs inside a fuel jet which draws mixture from a small reservoir of fuel The level of fuel is controlled by a float and valve At idle when the throttle is nearly closed the air valve is almost completely closed and the tapered needle which is attached to it restricts the flow of fuel to a great extent As the throttle is opened the air valve is drawn upwards allowing more air to enter and the needle is drawn out of the jet allowing more fuel to flow If the throttle is opened fully at low RPM the air valve rises about halfway As the engine speeds up and draws in even more air the air valve will continue to rise Thus the top half of the needle governs part throttle mixture and the lower half slim end governs full throttle mixture Mixture enrichment during acceleration is achieved using an oil filled damper which reduces the rate at which the air valve can rise Two types of needle are fitted a a rigidly fixed needle which should not touch the jet In some cases after stripping the carburettor it is necessary to centralise the needle and jet during re assembly this is a very early type b A needle which is spring loaded against the side of the jet when in good condition th
41. rcuitry being tested Gunson Gastester Professional Gunson Gastester Professional GASTESTER PROFESSIONAL Exhaust CO Gas amp Engine Analyser INDEX Page 1 Description and Features 7 2 Co Measurement 8 3 Tachometer 11 4 Dwell Meter 13 5 Voltage 16 6 Maintenance 18 7 Appendixes 19 7 1 Engine Exhaust Gas Analvsis 19 7 2 Common Problems Fuel Systems 20 7 3 Twin And Multiple Carburettors 22 7 4 Carburettor Types And Adjustments 22 7 5 Tachometer Dwell amp Distributorless Ignition 28 7 6 Alternator Starter And BatteryTesting 30 8 Specification 30 9 Technical Specification 30 10 Warranty 31 Gunson Gastester Professional FIGURE1 PRODUCT ILLUSTRATION WATER DRAIN at back DISPLAY GAS INLET GAS VENT PULSE PUMP CYLINDERS SWITCH FUNCTION GAS _ SWITCH OUTLET POWER LEADS RETAINING SPRINGS PIPE VEHICLE EXHAUST PIPE EXHAUST GAS PROBE Gunson Gastester Professional 1 Description and Features Gastester Professional is a combined exhaust gas CO analyser tachometer dwell meter and voltmeter with manv uses in motor car maintenance Though primarilv intended for multi cvlinder car engines the instrument may be used on motorcycles and single cylinder engines subject to the conditions in the SPECIFICATION on page 30 See also APPENDIX 2 item 5 Other caps are available should these not fit the vehicle s reservoir On receipt the cart
42. re correctly seated If necessary re seat the diaphragm by twisting the cap of the pump several times Obtain a replacement pump if these measures are not successful or alternatively return the complete instrument to Gunson Service Department if other faults are suspected If a baffled silencer with no tailpipe is fitted as on some motorcycles temporary restriction of the exhaust outlet or temporary fitting of a tailpipe extension may be the only way to achieve pulse pump operation and acceptable results CALIBRATION With extended frequent usage or impact while hot the GASTESTER PROFESSIONAL may develop a shift in the CALIBRATION setting position in air so that the 2 setting is not obtained at mid position of the calibration control Unless this drift is severe inaccuracies in the CO measurement are unlikely but this may be indicative of a build up in contamination in the collector box Under extreme circumstances this shift may prevent initial calibration being carried out contamination of the collector box or other damage is indicated and the product should then be returned for service For rectification or charge details please contact our service department with full details of product model and fault description NOTE An extra charge may be made for replacement of SEVERELY soiled external parts Gunson Gastester Professional 7 Appendixes 7 1 Exhaust Gas Analvsis Carbon monoxide chemical symbol CO isa colourless odourless
43. rnator charging voltage 13 4V to 13 6V minimum UNDER LOAD Typical alternator charging voltage 13 9V to 14 2V maximum NO LOAD For precise data refer to the particular vehicle service manual Note that alternators fitted to some older vehicles may not quite be able to carry the full electrical load of the vehicle In such cases refer to the alternator s rated specifications 4 INSTRUCTIONS ENGINE CRANKINGTEST The voltage range can be used to diagnose the presence of a faulty battery to give a strong guidance in the detection of starter motor faults and to lead the user to more specific tests for the other items of the starter cranking circuit such as the solenoid and battery terminals Before carrying out this test ensure that the battery has been recently fully charged a Put car out of gear and apply the handbrake b Disable the ignition by shorting the COIL HT lead to earth c Connect the BLACK lead to battery and the RED lead to battery and the BLUE lead to battery positive d Crank the engine using Gunson s Remotastart if available In bursts of 10 seconds for a total of 1 minute e Observe the scale A good battery fully charged will maintain specified values of voltage for at least 1 minute even under freezing conditions On the other hand a faulty battery even when recently charged will fail to hold these for more than a few seconds See APPENDIX 7 6 Voltages above specification combined with p
44. rofessional therefore receives 1 impulse per 2 revolutions With the Function switch set to 2 cylinders the scale reading should therefore be multiplied by 2 ie if the scale shows 1000 RPM actual speed is 2000 RPM This example is common on DISTRIBUTORLESS IGNITION SYSTEMS used on car engines except the FORD system see below and also 4 stroke MOTORCYCLES where the ignition sensor is camshaft driven Note If the above engine has an extra WASTED SPARK or if it is a two stroke engine with twice the number of sparks per revolution the reading would be correct on 2 cylinder setting This wasted spark and 2 stroke example is common on motorcycle engines for any number of cylinders as they often have a coil for each cylinder and a crankshaft driven ignition pickup points cam The FORD Distributorless Ignition System DIS requires special consideration In such systems there is one coil per 2 cylinders a 4 cylinder car having 2 coils The coils produce sparks every revolution one wasted and so the display gives a direct reading on the two cylinder range The Gastester Professional tachometer pickup is only connected to one of the coils Other car engines with DIS have one coil per cylinder and one spark per two rotations of the engine 2 Difficulty in connecting the Blue lead All vehicles that use spark ignition have a dc powered ignition coil excepting Magneto and CD 28 Gunson Gastester Professional ignition which is o
45. spare parts Check acceleration enrichment device 2 The correct mixture setting cannot be achieved Setting is continually too rich Remedy Clean the idle air bleed jet and air passage on fixed choke carburettors Check for severe needle jet wear on variable choke carburettors Check for high fuel level in the float chamber Check cold start device Setting is continually too weak 3 4 5 6 Gunson Gastester Professional Remedv Clean the idle jet on fixed choke carburettors Check needle and jet for disengagement from adjusting device or sticking on variable choke carburettors Check for air leaks The engine misfires or is unstable at idle with the correct mixture setting MISFIRE ENGINE INSTABILITV CAUSES INCREASE IN HC READING AND POTENTIAL EMISSION TEST FAILURE EVEN WITH CORRECT CO LEVEL Remedv Check for general engine condition compression pressures sparking plugs etc Check for air leaks these may cause severe variation in mixture between cylinders Investigate mixture quality i e fuel air mixture may not be finely atomised due to partially blocked air jets or prematurely feeding main jet system caused by high float chamber level etc Check for advanced ignition timing tight valve clearances slow idle speed The mixture setting drifts Remedy Check for leaking float chamber needle valve if CO level steadily increases with prolonged idle Check for high float chamber level Check Gastester
46. tapered needle in a jet Lowering the jet or raising the needle by manual adjustment causes a richening of the mixture throughout the operating range of the engine SU H I F TYPE J NEEDLE MIXTURE SCREW The following notes describe particular types of carburettors and the methods of adjustment 3 SINGLE FIXED VENTURI TYPE This is one of the simpler forms of carburettor with a single air inlet and throttle plate with a variety of air and petrol metering jets and channels The main jet and associated main air jet and emulsion tube etc provide an aerated emulsion which is fed to the venturi at speeds above idle This already aerated fuel and air mixture breaks down further in the airstream 24 Gunson Gastester Professional The idle circuit is separate and also has a fuel and an air jet which feed an aerated mix to a drilling downstream of the throttle plate further drillings are found in the area of the throttle plate Just above the idle drilling would be found progression holes which are progressivelv uncovered bv the movement of the throttle plate and increase the fuel flow when exposed to the manifold depression or vacuum This supplements idle fuel flow until the main fuel discharge in the venturi is well established All of these fluid circuits are fed from a small reservoir of fuel whose level is controlled by a float and needle valve 4 SINGLE VARIABLE VENTURE TYPE This type of carburettor consists of a single ai
47. the connection to the short length of wire taking care to remember to remove the wire at the end of the tests Alternatively a piece of stiff wire can be pushed into the connector alongside the lead Another useful improvisation for some connectors particularly the type often used by Vauxhall where the connector is a plastic covered plug is to use a paper clip trapped under the plug 3 Connection to a Distributorless Ignition System DIS Figure 15 se TITTI A s J The connection to a DIS system is made to the primary winding of either of the coils The coils are not always visible as separate coils but there is invariably a cable which leads to the primary windings In the Ford DIS system used on Fiesta Orion Escort etc the connection is to either of the outer connectors of the 3 way plug and socket mounted on the coil unit These connectors are numbered 1 and 8 It may be more convenient to make the connection to the other end of the lead which is to pin numbers 1 or 8 of the ECU multiway plug See Figure 4 Difficulty in obtaining a reading Check the connections to the car battery then remove the BLUE lead and connect to the other side of the coil If for any reason a 12V battery other than the car battery is used for the Red and Black leads of Gastester Professional it will be necessary to connect a common earth between the battery earth and the earth of the car 5 6v 24V and positive earth syste
48. ue lead connection has a high impedance it may be used without loading a circuit and will therefore not load or damage electronic circuits Note however that the GASTESTER PROFESSIONAL continuously draws approx 0 8 Amps from the POWER SUPPLY to the CO analyser i e the RED and BLACK clips LBATTERY CHARGE GENERAL INFORMATION A 12 volt lead acid battery has a nominal voltage of 12 6 volts A battery which never reaches the fully charged stage even after prolonged charging can be said to be ageing It may continue to give good service but a considerably reduced capacity for charge should be viewed with suspicion particularly if there are other symptoms of a suspect battery such as poor engine starting On the other hand it is entirely possible for a battery to fail while in the fully charged state or at least all except one cell to be fully charged and this mode of failure is quite common A measurement taken immediately after having a battery on charge or in a car with the engine running will show approx 0 5 volts higher than the normal 12 6 volt reading due to the accumulation of surface charge that is removed by the first modest current draw on the battery A battery takes several hours to settle down to a completely stable state even following a period of discharge and is preferably left say overnight However a reasonably accurate measurement of the state of battery charge can be obtained by switching on the car headlamps for 1
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