1994-1998 Medium Duty LPG Service Manual Supplement
Contents
1. Re AE Re Ge AE Re Ge AE Re Ge AE Re Ge AE Re Ge AE Re Ge Ai EE ee 27 een se ire GR ee Ge es Ee Ve Ee ed oe Eg dee ok Oe ba Ge ewe ee dbe Ge eb deed 27 UK EE OE ER EE EK EER EE N N 28 Adaptive Digital Processor ADP RE ER ER RE EE ER RR RE EE EER RR RE EE ER RR RE EE ER RR RE EE ER RR RE EE ER ER 28 IMPCOS PRONM uoo ee ee RE E 28 Rebuild Instructtons esse ee ee ER ER RE ER ER RE ER ER RE EER RR REGEER RR RR EER RR KEER RR RE EE nnus KERE ER RR KERE ER RR RE EE EER RE Ee ER nnn 29 jer AA AE EE VER OE RE N NE Ee 29 GEE EE EE EE EE Ee EE ED EE EE EE 30 Propane Fuel System InspectiON ese Re ER RE KERE AK KA AR REG ER EER AR KA nenne nnne RR Ee AR RE Ge nante ee RE Ee ee 30 SPOClal Le LEE 30 Specifications EE ER el Ee ee N EG SR GE ed N GE DE ee Re Ee ee Ee 31 UI Te EE DE EE OE E E OE OE OT OE OD EE 31 Technical recs se Ge SE AN ee Seed SE Dee ae Ve Se GR dao SE Oe a Ens eru ee TS 31 All information illustrations and specifications in this manual are based on the latest product information available at the time of publication IMPCO reserves the right to make changes at any time without notice No part of this manual may be reproduced stored in any retrieval system or transmitted in any form or by any means including but not limited to electronic mechanical photocopying and recording without prior written permission of IMPCO Technologies Inc 1998 IMPCO TECHNOLOGIES INC IMPCO2. Fuel System Checks Check for Rich or Lean symptom that causes the condition Drive the vehicle at the speed of the complaint Monitoring the oxygen sensors will help identify the problem Check the fuel pressure Refer to the Fuel System Pressure Test Check LPG mixer for proper installation and connection Check for proper operation of fuel control and idle control valves Ignition System Checks Check for the proper ignition output voltage using the spark tester J26792 or the equivalent Refer to Ignition System Check the spark plugs Remove the plugs and inspect them for the following conditions Wet plugs Cracks Wear Improper gap Burned electrodes Blistered insulators Heavy deposits e Check the spark plug wires by connecting an ohmmeter to the ends of each wire in question If the meter reads over 30 000 ohms replace the wires 1998 GM Medium Duty Chassis Service Manual Supplement Page 16 2 23 98 IMPCO PROPANE FUEL SYSTEM Engine Mechanical Check Perform a cylinder compression test Refer to Engine Mechanical Check the engine for the following Broken motor mounts Improper valve timing Low compression Bent pushrods Worn rocker arms Broken or weak valve springs Worn camshaft lobes Refer to Engine Mechanical in the OEM Service Manual Additional Checks Important The LPG system works on a fumigation principle of fuel introduction and is more sensitive to intake manifold leakage than the gasoline fuel supply
3. Hie 418 OS fld n wane ADP 1998 GM Medium Duty Chassis Service Manual Supplement Page 5 2 23 98 IMPCO PROPANE FUEL SYSTEM SYMPTOM DIAGNOSIS Before Using This Section Before using this section you should have performed the Powertrain On Board Diagnostic System Check and determined that 1 The Engine Control Module and MIL Malfunction Indicator Lamp are operating correctly 1 There are no Diagnostic Trouble Codes DTCs stored or a DTC exists but without a MIL Several of the following symptom procedures call for a careful visual and physical check The visual and physical checks are very important The checks can lead to correcting a problem without further checks which may save valuable time Important Preliminary Checks Visual and Physical Checks Check the Engine Control Module grounds for being clean tight and in their proper location Check the vacuum hoses for splits kinks and proper connections as shown on the Supplemental Vacuum Hose Routing Label Check for any type of leak or restriction Check for air leaks at all the mounting areas of the intake manifold sealing surfaces Check for proper installation of the propane mixer and adapter Check for air leaks at the propane mixer and adapter Check the ignition wires for the following conditions Cracking Hardness Proper routing Carbon tracking Check the wiring for the following items Proper connections Pinches Cuts
4. Check for a sticking fuel control or idle control valve Check the condition of the wiring to the primary and secondary lock off valves Additional Check Check for Electromagnetic Interference EMI EMI on the reference circuit can cause a missing condition Monitoring the engine RPM with a scan tool can detect an EMI A sudden increase in the RPM with little change in the actual engine RPM indicates EMI is present If the problem exists check the routing of the secondary wires and the ground circuit 1998 GM Medium Duty Chassis Service Manual Supplement Page 13 2 23 98 IMPCO PROPANE FUEL SYSTEM Poor Fuel Economy Gem a T DEFINITION Fuel economy as measured by an actual road test is noticeably lower than expected Also the economy is noticeably lower than it was on this vehicle at one time as previously shown by an actual road test Preliminary Checks e Refer to Important Preliminary Checks e Check the air cleaner element filter for dirt or being plugged e Visually Physically check the vacuum hoses for splits kinks and proper connections as shown on the Vehicle Emission Control Label e Check the owner s driving habits for the following items The A C ON full time Defroster mode ON Excessive idling or stop and go driving Tires at correct air pressure Low LPG refill quantity check gauge accuracy and fill valve operation Excessively heavy loads being carried Heavy acceleration too much
5. PROPANE FUEL SYSTEM VEHICLE APPLICATION This IMPCO propane system was designed to be installed on 1994 to1998 GM Medium Duty Chassis gt 14 000 GVWR with 6 0L and 7 0L V8 For non California vehicles the installation instructions and system content are based on the conversion of a stock gasoline powered vehicle Installation of this system on a previously altered and or converted gasoline powered vehicle may require repair or replacement of any previously altered base vehicle components PROPANE FUEL SYSTEM WARNING CAUTION Do not smoke carry lighted tobacco or use a lighted flame of any type when working on or near any fuel related component Highly flammable air fuel mixtures may be present and can be ignited causing personal injury CAUTION Do not allow propane to contact the skin Propane is stored in the fuel tank as a liquid When propane contacts the atmosphere it immediately expands into a gas resulting in refrigeration which can cause Severe burns CAUTION Do not allow propane to accumulate in areas below ground level such as in a service pit or under an alignment rack Propane is heavier than air and can displace oxygen creating a dangerous condition GENERAL DESCRIPTION PROPANE FUEL SYSTEM The primary components of the propane fuel system are the converter mixer electric lock off solenoids and electronic control unit The system operates at pressures up to 312 psi Propane is delivered from the
6. The following symptom tables contain groups of possible causes for each symptom and cover several engines The following symptom tables cover several engines The order of these procedures is not important If the scan tool readings do not indicate the problems then proceed in a logical order easiest to check or most likely to cause first In order to determine if a specific vehicle is using a particular system or component refer to the appropriate OEM Service Manual Symptom Verify the customer complaint Locate the correct symptom table Check the items indicated under that symptom 1998 GM Medium Duty Chassis Service Manual Supplement Page 6 2 23 98 IMPCO PROPANE FUEL SYSTEM Hard Start DEFINITION The engine cranks OK but does not start for a long time The engine does eventually run or may start but immediately dies Preliminary Checks Sensor Checks Fuel System Checks Ignition System Checks 2 23 98 Refer to Important Preliminary Checks Make sure the vehicle s operator is using the correct starting procedure e Check the Engine Coolant Temperature ECT sensor with the scan tool Compare the engine coolant temperature with the ambient air temperature on a cold engine If the coolant temperature reading is more than 5 degrees greater or less than the ambient air temperature on a cold engine check for high resistance in the coolant sensor circuit e Check the Throttle Position TP sensor If a
7. Check FCV for proper operation Additional Checks Proper E Prom calibration Check the EGR gasket for a faulty or loose fit Check for an EGR valve that is open all the time Refer to the OEM Service Manual 1998 GM Medium Duty Chassis Service Manual Supplement Page 18 2 23 98 IMPCO PROPANE FUEL SYSTEM 1998 GM Medium Duty Chassis Service Manual Supplement Page 19 2 23 98 IMPCO PROPANE FUEL SYSTEM FUEL SYSTEM PRESSURE CHECK Special Tools ITK 1 IMPCO test kit Step Action Value s Yes No 1 Close the propane manual shut off valve 1 Remove regulator primary test port plug and install a gauge capable of reading 0 10 psi Note A small amount of fuel will be present behind the plug 1 2 psi 1 Open the propane manual shut off valve 1 Start the vehicle Monitor the primary pressure gauge under various operating conditions Is the pressure within the specified range E Ge 1 Remove regulator secondary test port plug and install a gauge capable of reading negative inches of water column 1 Disconnect fuel control valve FCV 1 to 2 w c 1 Start vehicle Monitor secondary pressure gauge under various operating conditions T v Go To Step 6 Go To Step 5 Is the pressure within the specified range Observe regulator primary pressure gauge Is pressure greater than specified value Go to Step 5 Go to Step 4 Verify that liquid fuel is available from the tank Verify that the propane manual sh
8. Check oxygen sensor operation Fuel System Checks e Check for proper secondary regulator pressure e Verify that the FCV is not leaking vacuum into the regulator diaphragm chamber when checking secondary pressure If the FCV sticks open it will cause lean fuel mixtures e Verify that the ICVs are functioning properly Erratic driveability problems can be the result of malfunctioning ICVs e Verify FCV vacuum connections to air valve vacuum e Check mixer air valve for build up dirty e Verify correct air gas valve application e Check for engine vacuum leaks e Check for air leaks downstream of the mixer Additional Checks e Check oxygen sensor connection to ADP e Check for proper ADP connections Idle Rich Checks sf Action Cd DEFINITION The ICV duty cycle readings on the FSA are below 20 and or the oxygen sensor always indicates rich Sensor Checks e Check oxygen sensor operation Fuel System Checks e Check for proper secondary regulator pressure e Verify that the FCV is not stuck closed If the FCV sticks open it will cause lean rich mixtures e Verify that the ICVs are functioning properly Erratic driveability problems can be the result of malfunctioning ICVs e Check mixer air valve for build up dirty e Check air gas valve and mixer for wear e Verify FCV vacuum connections to air valve vacuum Additional Checks e Check all vacuum hoses for proper connection or deterioration e Check for proper ADP connect
9. Unstable or Incorrect Idle Stalling Reconnect the IAC motor with the ignition OFF If there is no RPM drop on one or more of the cylinders or excessive variation in drop check for spark on the suspected cylinders with a J 26792 or the equivalent If there is no spark refer to Ignition System in the OEM Service Manual If there is a spark remove the spark plugs in these cylinders and check for the following conditions Insulation cracks Wear Improper gap Burned electrodes Heavy deposits Check the spark plug wire resistance should not exceed 30 000 O Check the distributor rotor and the distributor cap If the previous check did not find the problem visually check the following items The ignition system for moisture dust cracks burns etc With the engine running spray the plug wires with a fine water mist to check for shorts Engine Mechanical Checks Perform a cylinder compression check Refer to Engine Mechanical Check the engine for the following Improper valve timing Bent pushrods Worn rocker arms Worn camshaft lobes Broken or weak valve springs Refer to Engine Mechanical Check the intake and exhaust manifold passages for casting flash Refer to Engine Mechanical 1998 GM Medium Duty Chassis Service Manual Supplement Page 12 2 23 98 IMPCO PROPANE FUEL SYSTEM Fuel System Checks Check the fuel system plugged fuel filter low fuel pressure etc Refer to Fuel System Pressure Check
10. clean all parts to be reused The RK TPEV kit contains all of the necessary parts to replace the components that are subject to deterioration Re assemble the back cover C1 21 and gasket G1 35 to the heat exchanger body AB1 19 Replace the six S1 3 screws as necessary match the mounting bosses in the cover with those on the heat exchanger Tighten the screws in a crossing pattern The AB1 19 has a recess that has been cast into the body to locate the sponge The recess is approximately 040 inch deep so the sponge must be located accurately Install the primary seat S4 7 Install the body B1 20 and body gasket G1 37 Mount the body gasket on the primary pin boss and the two locating pins on the underside of the body Use two S1 39 screws to locate the body on to the heat exchanger body AB1 19 Tighten the screws to hold the units in place Install the primary valve pin P1 11 Install the primary diaphragm assembly AD1 15 over the locating pins and screw bosses This gives the 23 24 25 26 27 proper alignment for the assembly of the springs and the cover Place the two primary valve springs S2 13 upon the locating perches that are extruded from the back up plate on the primary valve diaphragm assembly AD1 15 Press the primary cover C1 20 in place over the primary valve springs and the diaphragm assembly Insert the S1 40 screws The protruding cups in the cover house the primary springs Inst
11. e Verify that FCV is functioning properly Erratic driveability problems can be the result of a malfunctioning FCV e Check mixer air valve for build up dirty e Check air gas valve and mixer for wear e Check air intake system for restrictions Engine Mechanical Check Cruise Lean Checks L eon DEFINITION Mixture duty cycle readings on the FSA are above 80 and or the oxygen sensor always indicates lean when the engine is operating off idle at low load Sensor Checks e Check for proper oxygen sensor operation Fuel System Checks e Verify that the ICVs are functioning properly Erratic driveablity problems can be the result of malfunctioning ICVs e Validate proper FCV connection to air valve vacuum e Check for proper primary and secondary regulator pressure e Check for a plugged propane fuel filter Additional Checks e Check for air leaks downstream of the mixer 1998 GM Medium Duty Chassis Service Manual Supplement Page 23 2 23 98 IMPCO PROPANE FUEL SYSTEM Cruise Rich DEFINITION Mixture duty cycle readings on the FSA are below 20 and or the oxygen sensor always indicates rich when the engine is operating off idle at low load Fuel System Checks Check mixer air valve for build up dirty Check air gas valve and mixer for wear Check for proper primary and secondary regulator pressure validate steady pressure readings at wide open throttle If pressure fluctuates troubleshoot and repair
12. esee 10 Hesitation Sag Stumble eee eese eene EE AE ee 11 Cuts Out MISSES 35 ee iuri rri EE er 12 Poor Fuel Economy RE REG RR RE EER RR RE RE GR RR RE REG KAR KERE GR RR KERE GR RR KERE GR RR RE nnns 14 Rough Unstable or Incorrect Idle Stalling ies see ee EG AE ee en 16 Backtire Es ee EE oe ee E ee Gee ER Re ee EE ee ED 18 Fuel System Pressure Check eese A RR ER KEER KERR seen nennen nn Ee AR Ke AR Ke Ge NEEN 19 Mechanical Diagnosis RE ER ER RE ER RR RE EER KERKE EER RR RE ER RR KERE ER RR KERE GR RR KERE ER RR RE Ee EER Een 20 CONVE E LE LR HEEL EE EN 20 DEEN EA ADP Initialization iss ee 23 IMPCO diie EE N EE EE EE N ee durar 24 On Vehicle Services gees Ge Ese EELER P 25 Propane Fuel System Pressure Relief RE AR RA AR RAGE EE eene 25 Propane Fuel System Leak Test esse see EER KA AR KEER ER KEER RE RA AR RE GR RR ERA RE AAR KRAAK KEER en 25 Propane Fuel Filter ee EE ninnan ee see Ke EE ee ede ande ee Ee Ee Ge aa dee ee 25 Electric Lock off Solenoids RE AR KA AR KEER ER KEER RR essen ER RE AR RR AAR RR Ge ER KEER ee 26 MT oe AE EE N EE EE EE 26 Uhderhood ae Gee de GO ee 26 FuelGontrol Valerie ee EE 27 Teler ige BL ORE ER EE EE EE EE EE EE EN EE EN 27 Regulator Control Valve RCV
13. sticking throttle shaft or binding linkage causes a high TP sensor voltage open throttle indication the Control Module will not control the idle Important A partially closed propane manual shut off valve may create an extended crank condition e Check the fuel system pressures Refer to the Fuel System Pressure Test e Check mixer and adapter assembly for proper installation and leakage e Check fuel control and idle control valve operation Note Propane being a gaseous fuel requires higher secondary ignition system voltages for the equivalent gasoline operating conditions Peak ignition voltages are experienced during crank conditions A thorough ignition system inspection should be performed e Check for the proper ignition voltage output with J 26792 or the equivalent Check the spark plugs for the following conditions Wet plugs Cracks Wear Improper gap Burned electrodes Heavy deposits Check for bare or shorted ignition wires Check for moisture in the distributor cap if applicable Check for loose ignition coil connections Check for loose Control Module or ignition system grounds Check the Ignition Control IC circuit for an open or short to ground 1998 GM Medium Duty Chassis Service Manual Supplement Page 7 IMPCO PROPANE FUEL SYSTEM Engine Mechanical Checks Important The propane fuel system works on a fumigation principle of fuel introduction and is more sensitive to intake manifold leakage than the gas
14. system Check for vacuum leaks Vacuum leaks can cause a higher than normal idle and low Idle Air Control IAC counts Check the IAC operation Check the Control Module grounds for being clean tight and in their proper locations Check the scan tool to determine if the Control Module is receiving an A C signal If a problem exists with the A C ON check the A C system operation Refer to the OEM Service Manual Check for EGR being ON while idling which will cause roughness stalling and hard starting Check the battery cables and ground straps They should be clean and secure Erratic voltage will cause the IAC to change its position resulting in poor idle quality Check the IAC valve The IAC will not move if the system voltage is not within 9 to 16 volts Check the A C refrigerant pressure for being too high or for a faulty high pressure switch Check the Crankcase Ventilation Valve for proper operation by placing a finger over the inlet hole in the valve end several times The valve should snap back If not replace the valve 1998 GM Medium Duty Chassis Service Manual Supplement Page 17 2 23 98 IMPCO PROPANE FUEL SYSTEM Backtire Gee Am DEFINITION The fuel ignites in the intake manifold or in the exhaust system making a loud popping noise Preliminary Check e Refer to Important Preliminary Checks Ignition System Checks Note Propane being a gaseous fuel requires higher secondary ignition sy
15. the required fuel flow rate required to maintain a precise air propane fuel mixture across the entire engine operational range The ADP controller does not require any service or scheduled maintenance The ADP incorporates an engine MAP Manifold Absolute Pressure sensor and engine RPM input Feedback information from the oxygen sensor is used to update the digital block learn memory By 1998 GM Medium Duty Chassis Service Manual Supplement Page 2 2 23 08 storing this information the ADP can instantly correct for proper air fuel ratios under different operating conditions When the oxygen sensor sends a voltage above 450 mV the ADP interprets that the fuel mixture is rich The ADP will increase the duty cycle of the fuel control valve FCV increasing the vacuum signal on the top of the regulator secondary diaphragm This closes the secondary valve slightly which reduces fuel flow An oxygen sensor voltage of less than 450 mV is interpreted as a lean condition and vacuum is decreased This increases fuel flow The ADP block learn memory is non volatile If the battery is disconnected the memory will not be lost The memory can be erased at any time by removing the ADP jumper connector as described in ADP Initialization On the first start up after the memory has been erased the set up procedure allows the ADP to enter a fast learn stage to update the internal memory cells within a very short period of time After the
16. to the converter main bracket 18 Remove the lock off from the converter 19 Transfer fittings to new lock off using a liquid thread sealing compound emt oh ON Installation Important e Do not use Teflon tape on any fuel fitting Use a liquid pipe thread sealant when installing fittings Install in reverse order of removal Replace all gaskets during re assembly Tighten fuel fittings finger tight plus 1 to 2 turns Tighten fuel line fittings to 16 20 lb ft Leak check the system using a liquid leak detector Qr d om cx 1998 GM Medium Duty Chassis Service Manual Supplement Page 27 2 23 98 IMPCO PROPANE FUEL SYSTEM FUEL CONTROL VALVE FCV Removal 1 Relieve the propane fuel system pressure Refer to Propane Fuel System Pressure Relief 2 Disconnect the negative battery cable 3 Remove the air cleaner 4 Disconnect the FCV electrical connector 5 Disconnect the three 3 hose from the FCV and remove the valve Installation 1 Install in reverse order of removal IDLE CONTROL VALVE ICV ech Relieve the propane fuel system pressure Refer to Propane Fuel System Pressure Relief 2 Disconnect the negative battery cable 3 Remove the air cleaner 4 Disconnect the ICV electrical connector 5 Disconnect the three 3 hoses from the ICV and remove the valve Installation 1 Install in reverse order of removal REGULATOR CONTROL VALVE RCV Removal 1 Relie
17. ADP passes this fast learn stage corrections slow down to provide stable performance for the rest of the vehicle fuel system s service life IMPCO PROGRAMMABLE READ ONLY MEMORY PROM The IMPCO DSM incorporates most base vehicle diagnostic and control functions while optimizing spark advance specifically for propane to provide reduced emissions The DSM is available as a replacement part only and cannot be re programmed in field The following base vehicle calibrations are modified by the IMPCO DSM e Timing curve EGR diagnostics e O2 Sensor diagnostics The following base vehicle calibrations are disabled by the IMPCO DSM e Injector circuit e Evaporative Emission Control Diagnostics ELECTRIC LOCK OFF SOLENOID The electric lock off solenoid provides electronic fuel shut off for pressures up to 312 psi It is a closed solenoid operated lock off with a 1 4 IMPCO PROPANE FUEL SYSTEM diameter fuel orifice If the lock off module fails it is designed to fail in the closed position The solenoid has a high temperature coil and is both UL and CGA approved FUEL AND IDLE CONTROL VALVES FUEL CONTROL VALVE FCV An electrically actuated control valve used to trim off idle fuel mixtures by controlling the pressure on top of the regulators secondary diaphragm Controlled by the ADP the valve is used to translate a duty cycle into a regulated vacuum signal The fuel control valve will either meter air valve v
18. EE Y A Service Manual Liquefied Petroleum Gas LPG Fuel System for 1994 1998 GM Medium Duty Chassis C 60 C 70 with 6 0L and 7 0L V8 CONTENTS VI dl ER ele VE 1 Propane Fuel System Warning u eeuse see EE Ee KA AR KRAKE KEER RR AAR REG ER KEER KEER aan nannten KRAAK GR RR Re ee EE Ee nna 1 General Neg LE OR N N OE N N N ge 1 Propane Fuel System siese ge ve kk ge gee we ek Ge en Oe ee Ee Re t ska cod Wee eg acu RD dee RR 1 Once ee RR E en es we Se Ge Reed ww Gee ge eke 2 GEE ER DE N EE EE N EE EE NE EE EN 2 Adaptive Digital Processor ADP ese ee RE ER EE RR ER EE RE ER EE RE EER KERE GE RR ER RE GE EER RR RE GE ER EE EE 2 IMPCO Programmable Read Only Memory PROM s s ssssssssssssssssssesssessseseseees 3 Electric Lock off Solenoid esse Re ER RE KERE AR RA AR EER KERE esee RR Ka GR EE Ee AR Ke AR KRAAK ERG EE RE Ee ee 3 Fuel and Idle Control Valves ees seke ER RE ER RE EK AR REG RR KEER KERE seen nnne EER EK EE AR RE nannten EE Ee ee 3 Regulator Control Valve RCV esse es see RA Ee Ge AE Ee Ge AE Re Ge esee Re Ge AE Ee Ge AE Ge AE ee en A RUE Ile TE 5 Electrical SchematIiC ie re dee See EENS NEEN 5 Symptom Diagnosis re De 6 Important Preliminary Checks ees sesse ek Re ER RE EE EE RE AR KA AR KEER EE EE AR RE AAR Rae EE Ee ee Ka 6 Hard Start sees EEEE E AEA AE EE 7 le E el Te e 9 Lack of Power Sluggishness or Sponginess
19. Refer to Fuel System Pressure Check Verify that the propane manual shut off valve is open Verify that the excess flow valve has not closed Check for proper operation of the fuel control and idle control valves Check the fuel filter and lines for restrictions Check for the proper ignition output voltage using the spark tester J26792 or the equivalent Refer to Ignition System Check the spark plugs Remove the plugs and inspect them for the following conditions Wet plugs Cracks Wear Improper gap Burned electrodes Heavy deposits Check the Control Module grounds for being clean tight and in their proper locations Check the generator output voltage Check the vacuum hoses for kinks or leaks Refer to the Vehicle Emission Control Information label Check for an Intermittent EGR problem Check for Torque Converter Clutch TCC operation Refer to Transmissions 1998 GM Medium Duty Chassis Service Manual Supplement Page 9 IMPCO PROPANE FUEL SYSTEM Lack of Power adm ge EE or Sponginess DEFINITION The engine delivers less than power There is little or no increase in speed when partially applying the accelerator pedal Preliminary Checks e Refer to Important Preliminary Checks e Compare the customer s vehicle with a similar unit Make sure the customer has an actual problem Do not compare the power output of the vehicle operating on propane to a vehicle operating on gasoline The fuels
20. Verify that the ICVs are functioning properly Erratic problems can be the result of a malfunctioning ICVs Verify FCV vacuum connections to air valve vacuum Additional Checks Check air intake system for restrictions Check all vacuum hoses for a T Sp pim connection or deterioration Exhaust Exhaust System Checks Checks ADP INITIALIZATION Tools Required IMPCO Fuel System Analyzer FSA Or Dwell Meter set to six cylinder scale Important e Initialization of the ADP is required after any major engine service or fuel system repair e lf the engine and oxygen sensor are hot voltage could be above 0 5 volts The red LED on the ADP may remain off for several seconds 1 Disconnect the two 2 pin connector jumper P14 located in the passenger compartment near the HVAC blower motor 2 Atest connector P19 is located in the engine compartment near the heater core and allows access to the oxygen sensor and fuel control valve FCV signals Note Some models may not be equipped with a test connector To initialize these vehicles access the necessary signals directly If using a FSA connect as follows e Black to ground e Red to power e Green clip to oxygen sensor signal tan wire e Yellow clip to fuel control valve FCV signal yellow wire If using a dwell meter connect as follows e Check for exhaust leaks 00000000 for exhaust leaks e Black to ground e Red to power e Dwell lead to f
21. When using both methods use the electronic leak detector first to avoid contamination by the liquid leak detector PROPANE FUEL FILTER Removal 1 Relieve the propane fuel system pressure Refer to Propane Fuel System Pressure Relief 2 Disconnect the negative battery cable 3 Disconnect the fuel inlet line from the filter 4 Remove the nut retaining the filter clamp 5 Unscrew the filter from the electric lock off Installation 1 Coat the male pipe threads with a liquid thread sealant compound 2 Install and tighten the filter into the lock off assembly Install and secure the filter clamp and nut Connect the fuel inlet line to the filter and tighten Open manual shut off valve Reconnect battery and the start vehicle Leak check the fuel system using a liquid leak detector DO noc ELECTRIC LOCK OFF SOLENOIDS Underbody Removal 1 Relieve the propane fuel system pressure Refer to Propane Fuel System Pressure Relief 2 Disconnect the negative battery cable 3 Remove the propane fuel filter Refer to Propane Fuel Filter 4 Disconnect the electric lock off solenoid electrical connector 5 Disconnect the fuel line 6 Remove the two 2 electric lock off solenoid mounting bolts 7 Remove the lock off from the bracket 8 Remove the elbow fitting from the fuel outlet port Installation Important e Do not use Teflon tape on any fuel fitting Use a liquid pipe thread s
22. acuum to the regulator to lean fuel mixtures or reference atmospheric pressure to richen fuel mixtures IDLE CONTROL VALVE ICV Two electrically actuated control valves are used to introduce either fuel or air into the mixer bore Controlled by the ADP the idle control valves will allow either fuel air or a mixture of both into the mixer below the air valve The idle control valves will go to a fixed position after the fuel control valve becomes active REGULATOR CONTROL VALVE RCV The regulator control valve RCV is mounted on the regulator cover The RCV is a one way check valve that opens at 8 10 of water column and permits quick response of the secondary diaphragm during wide open throttle operation 1998 GM Medium Duty Chassis Service Manual Supplement Page 3 2 23 98 IMPCO PROPANE FUEL SYSTEM 1998 GM Medium Duty Chassis Service Manual Supplement Page 4 2 23 98 IMPCO PROPANE FUEL SYSTEM DIAGNOSIS ELECTRICAL SCHEMATIC RL VIN SSINYYH ZO d mis ONSNOH 1v150mi34 ZL OD Zut BOD NOLINDI 330 3001 Avid H FOTO tid 440 3001 AANONOOSS lid 22 Bid Jis Ol Bt i On 9 H Y Ow 09 gui fd 8 07 0601 8 01 8601 X18 0 3601 30123880 093 SS3NUYH JVHN 038 08 Kal E DOENE 39 is IR moi 940 08 Brot 1 OONTIOS NOI Um 09 Ki 038 01 Gu Q38 01 vel UL O38 o t 30123NN02 Ian 4 B0 Do ow gi x8 OS St x9 07 Did Oa BOLIINNOD ISIL YSi
23. all all of the screws except for the one required for fulcrum pin installation Tighten the primary cover screws until they just make contact with the body Then tighten the screws solidly in a diagonal pattern until all the screws are tight Replace the secondary lever and seat with the new assembly supplied in the kit 1998 GM Medium Duty Chassis Service Manual Supplement Page 30 2 23 98 IMPCO PROPANE FUEL SYSTEM Install the secondary lever and insert the fulcrum pin P1 7 Replace the final S1 39 screw at this time Tighten the final screw 31 Using a straight edge or G2 2 gauge check the lever height The secondary lever link pin should be approximately 1 32 inch below the level of the body casting 32 Replace the secondary spring Slip the spring under the secondary lever making sure it is retained by the two tabs at the sides and the single tab punched through the top of the lever 33 Install the secondary diaphragm Verify that the slotted diaphragm link is engaged with the link pin 34 Replace the cover AC1 22 1 Turn all eight of the S1 3 screws until they contact the cover Tighten the screws in a diagonal pattern until they are all firmly seated 35 The converter is now complete Check the converter for leakage using soap suds or a compatible testing solution MIXER 1 Remove the mixer from the engine and place it on a suitable work surface 2 Remove the four S1 3 screws that secure the C1 30 diaphragm cov
24. ealant when installing fittings Install in reverse order of removal Tighten fuel fittings finger tight plus 1 to 2 turns Tighten fuel line fittings to 16 20 lb ft Leak check the system using a liquid leak detector BOD 1998 GM Medium Duty Chassis Service Manual Supplement Page 26 2 23 98 IMPCO PROPANE FUEL SYSTEM Underhood Removal 1 Relieve the propane fuel system pressure Refer to Propane Fuel System Pressure Relief Disconnect the negative battery cable Disconnect the hot and cold air ducts Remove the air cleaner Disconnect the fuel supply hose Disconnect the coolant hoses NOTE be sure to relieve cooling system pressure prior to disconnecting the coolant lines Disconnect the FCV electrical connector Disconnect the fuel and idle control valve electrical connectors 9 Remove the four 4 rear support brackets bolts 10 Remove the two 2 bolts that retain the converter main bracket to the throttle body adapter 11 Remove the four 4 bolts that retain the mixer plate to the throttle body adapter 12 Remove the mixer converter module from the engine 13 Disconnect the hose from the RCV valve and remove the RCV valve 14 Disconnect the vacuum hose from the converter that comes from the fuel control valve 15 Unscrew converter from the mixer assembly 16 Remove the bolts that retain the lock off to the converter main bracket 17 Remove the bolts that retain the converter
25. ect the ADP electrical connector 3 Remove the mounting bolts and the ADP Installation 1 Install in reverse order of removal 2 Initialize the ADP Refer to ADP Initialization in Mechanical Diagnosis IMPCO PROM Refer to the OEM service manual for removal and installation instructions Note Install only a genuine IMPCO replacement PROM assembly installation of the OEM gasoline PROM will result in decreased engine performance and possible engine or exhaust system damage 1998 GM Medium Duty Chassis Service Manual Supplement Page 29 2 23 98 IMPCO PROPANE FUEL SYSTEM REBUILD INSTRUCTIONS CONVERTER Under normal conditions installation of a complete rebuild kit should be necessary only at the time of a major engine overhaul or when the converter has been out of service for a long period of time Gaskets and diaphragms may deteriorate if the converter is stored after being used 1 2 DIEP 20 21 22 Remove the diaphragm cover AC1 22 1 by taking out the eight screws around the circumference of the cover Remove the secondary diaphragm assembly AD1 23 This requires the assembly to be moved about one inch away from the gas outlet to disengage the two prongs of the diaphragm link from the lever The diaphragm and cover are removed revealing the secondary lever with the valve and spring Remove the screw that retains the fulcrum pin Slide out the fulcrum pin P1 7 Remove it completely from
26. er in place 3 Remove the diaphragm cover and the S2 30 diaphragm spring 4 Lift the air valve assembly out of the mixer body 5 Remove the diaphragm from the air valve assembly by removing the 4 S1 22 retaining screws 6 Clean and inspect all parts Inspect the air gas valve and the body assembly for evidence of wear If scratches damage marring or a wear ridge or step exist these parts must be replaced 7 Reassemble in the reverse order of disassembly Torque the S1 40 and S1 19 screws to 15 Ib in 8 Reinstall the mixer to the engine PROPANE FUEL SYSTEM INSPECTION Inspect the propane fuel system hoses and vacuum lines for cracks wear or other damage Replace if necessary Inspect the propane fuel system brackets for cracks deformation or other damage Replace if necessary Inspect all fasteners and service as necessary SPECIAL TOOLS Liquid Leak Detector IMPCO ITK 1 IMPCO FSA 1 Qty 2 GM PROM Removal Tool 1998 GM Medium Duty Chassis Service Manual Supplement Page 31 2 23 98 IMPCO PROPANE FUEL SYSTEM SPECIFICATIONS TUNE UP Spark Plug Gap 0 032 TECHNICAL Fuel Control Valve FCV Idle Control Valve ICV Operable Temperature Range esent ener Re ee enses snnt enne 40 F to 257 F Electrical ll el Ee EE 9 6 volts DC Maximum VAE EE 15 0 volts DC selle lle EE 23 ohms Electric Lock off Solenoid Working pressures ert EE ER RE AO EE AR EP ERES Maximum 312 PSIG Nominal Operating Volta
27. fice or seat Disassemble regulator and perform inspection obstructed EXCESSIVE FUEL Incorrect secondary spring Check for proper spring application FLOW installed Incorrect secondary lever Adjust lever height using G2 2 gauge or height appropriate repair instructions Defective damaged or Disassemble inspect and repair as necessary contaminated primary or secondary seat Defective or damaged Inspect and repair regulator as necessary primary or secondary diaphragm Primary pin sticking in bore Disassemble inspect and repair as necessary REGULATOR VAPORIZ Poor coolant flow or low on Check coolant level and condition of coolant ER ASSEMBLY coolant FREEZING Air trapped in converter Purge air from cooling system Coolant passages blocked Remove vaporizer and clean passages or restricted Severe leakage of primary Verify converter operation diaphragm or primary seat COOLANT FOUND IN Porous or cracked heat Replace heat exchanger PRIMARY OR exchanger SECONDARY CHAMBER OF REGULATOR EXTERNAL COOLANT Leaking heat exchanger Replace gasket LEAKAGE FROM HEAT gasket G1 35 EXCHANGER COVER Porous or cracked heat Replace heat exchanger exchanger 1998 GM Medium Duty Chassis Service Manual Supplement Page 21 2 23 98 IMPCO PROPANE FUEL SYSTEM ADP Idle Lean Checks DEFINITION The ICV duty cycle readings on the FSA are above 80 and or the oxygen sensor always indicates lean Sensor Checks e
28. for changes in altitude 1998 GM Medium Duty Chassis Service Manual Supplement Page 1 2 23 08 IMPCO PROPANE FUEL SYSTEM CONVERTER The IMPCO Model E converter is a combined pressure regulator and vaporizer The regulator is a negative pressure two stage configuration which is closed when the engine is not running When the engine is cranking or running a partial vacuum is created in the fuel line to the regulator This opens the regulator permitting fuel to flow to the mixer The regulator receives liquid fuel at tank pressure The pressure is reduced in two stages to slightly less than atmospheric In the first stage the pressure is reduced to 1 2 psi Also during this stage the liquid fuel is vaporized by heating the base of the converter with e ngine coolant A sponge located in the primary chamber absorbs any liquid fuel and prevents it from entering the secondary chamber In the second stage the vaporized fuel is drawn into the secondary chamber where the pressure is reduced to negative 1 5 1 8 of water column MIXER The IMPCO Model 425 mixer is an air fuel metering device and is completely self contained It requires no linkage or idle vacuum line to the intake manifold The mixer is an air valve design utilizing a relatively constant pressure drop to draw fuel into the mixer from cranking to full load The vacuum applied to the air valve working against a spring located on top of the valve correctly posit
29. ge ie ee ee Ge AA RR Ge AA Re RR Ge AA Ge ee ee ee Re nnn snnt nen 12 16 volts DC nominal eine e Elte 6 2 10 Ohms Working Temperaire i EE OO EE e er EE EE EE N 40 to 250 F Typical Operation at 40 F Maximum Voltage required to open Main Valve ee se ee GR AA Ge AA ee ee AR Re nnne 5 5 volts DC Mo aT BILE 75 amps EK il Tuer euer CEET 1 Amp LIQUID PETROLEUM GAS Commercial Propane Butane Bollirig polnt F 930 Te WEE LL drm 32 Specific gravity of air 60 F 30 Ho UE 2 00 Specific gravity of water 60 F 30 Ho 0 5 ihe tester 0 58 Weight per gallon 60 Foririnte danaa abaka AA Ge aiar GR AA ee AA nnne 4 24H ME AR EE 4 85 B T U per gallon vaporized skree ee er eee ee ke eset ee Re ee ee ke ee ee Re ee ee ee ke ee ee 911 500 155 esee 102 600 B T U per pound vaporized iese sees se ee ee ee ee EEREN EREI Ee ee ee ee ee ee ee 21 560 RE dee 21 180 Air Fuel Ratio BY eu 29 10 WE EE N 30 to 1 Best AE AE ie ei cete ceca e eun tere EE N By Weight 14 8 to 1 14 8 to 1 Vapor Pressure Lbs Sq In Propane Butane STO VE At ER unen E TEE AE EE RR Mk abit isi ege 92 9E TE GOH Ee esse gee bees ee AE ER A EE terre 1002 ees 124 S d ege ei tue enis 22 5 UE 1903 teet 37i JI I EE N EE EEU SE EE eter 55 Propane Butane Octane number RON only AAA RE EE EE inns 91 Octane number as it relates to gasoline a
30. have different drive feel characteristics e Remove the air filter and check for dirt or restriction e Check the transmission shift pattern and the downshift operation Refer to Transmission Controls section Fuel System Checks Check for a restricted fuel filter contaminated fuel or improper fuel pressure Refer to Fuel System Pressure Test Sensor Checks Check the Manifold Absolute Pressure MAP sensor Check the Exhaust Gas Oxygen EGO sensor Ignition System Checks e Check for the proper ignition output voltage with the spark tester J 26792 or the equivalent e Check the Knock Sensor KS system Exhaust System Checks e Check the exhaust system for a possible restriction Refer to Engine Exhaust e Inspect the exhaust system for damaged or collapsed pipes Inspect the muffler for heat distress or a possible internal failure Engine Mechanical Check Check the engine for the proper operation of the following items Engine compression Valve timing Improper or worn camshaft Refer to Engine Mechanical Additional Check Check the Control Module grounds for being clean tight and in their proper locations Check the EGR Valve for being open or partially open all the time Refer to EGR System Check Check the A C operation Check for Torque Converter Clutch TCC operation Refer to the Torque Converter Clutch Solenoid in Automatic Transmission Check the generator output voltage Refer to Engine Electrical Check for a stre
31. he ECM will and repair instructions to restore the data stream cause poor operation and possible damage to before proceeding electric components When removing a new IMPCO PROM from its packaging check the Check the vehicle ignition timing Timing must be part number to verify that it is the correct part set to the manufacturer specifications shown on for your vehicle 1998 GM Medium Duty Chassis Service Manual Supplement Page 25 2 23 98 IMPCO PROPANE FUEL SYSTEM ON VEHICLE SERVICE PROPANE FUEL SYSTEM PRESSURE RELIEF CAUTION The propane fuel system operates at pressures up to 312 psi To minimize the risk of fire and personal injury relieve the propane fuel system pressure where applicable before servicing the propane fuel system components To relieve propane fuel system pressure 1 Close the manual shut off valve MSV on the propane fuel tank 2 Start and run the vehicle until the engine stalls 3 Turn the ignition switch OFF Note Residual vapor pressure will be present in the fuel System Ensure the work area is well ventilated prior to removing any fuel lines PROPANE FUEL SYSTEM LEAK TEST CAUTION Never use an open flame of any type to check for propane fuel system leaks Always inspect the propane fuel system for leaks after performing service Check for leaks at the fittings of the serviced or replaced component Use a commercially available liquid leak detector or an electronic leak detector
32. ing crank A thorough ignition system inspection should be performed Check for the proper ignition voltage output with J 26792 or the equivalent Check ignition timing Check for faulty spark plug wires Check for fouled spark plugs Check for an open ignition system ground Refer to Ignition System Check the Service Bulletins for PROM updates Check for manifold vacuum or air induction system leaks Check the generator output voltage Refer to Engine Electrical Check the EGR valve operation 1998 GM Medium Duty Chassis Service Manual Supplement Page 11 IMPCO PROPANE FUEL SYSTEM Cuts Out Misses Gem Am DEFINITION A surging or jerking that follows engine speed usually more pronounced as the engine load increases which is not normally felt above 1500 RPM or 48 km h 30 mph The exhaust has a steady spitting sound at idle low speed or hard acceleration for the fuel starvation that can cause the engine to cut out Preliminary Checks e Refer to Important Preliminary Checks Ignition System Checks e Check ignition timing Check for a cylinder misfire 1 Start the engine 1 Allow the engine to stabilize 1 Then disconnect the Idle Air Control IAC motor Notice In order to prevent damaging the catalytic converter do not perform this test for more than 2 minutes Remove one spark plug wire at a time using insulated pliers If there is a RPM drop on all cylinders equal to within 50 RPM go to Rough
33. ions 1998 GM Medium Duty Chassis Service Manual Supplement Page 22 2 23 98 IMPCO PROPANE FUEL SYSTEM Wide Open Throttle Lean Checks Action o O DEFINITION Mixture duty cycle readings on the FSA are above 80 and or the oxygen sensor always indicates lean when operating near full throttle Fuel System Checks Check propane fuel level Check for a plugged propane fuel filter Verify that the manual fuel shut off valve is fully open Verify that the excess flow valve in the manual fuel shut off valve is not closing under high flow conditions Check for proper primary and secondary regulator pressure validate steady pressure readings at wide open throttle If pressure fluctuates troubleshoot and repair Verify that FCV is functioning properly Erratic driveability problems can be the result of a malfunctioning FCV Ignition System Checks e Check ignition system operation Exhaust System Checks e Check for exhaust leaks Engine Mechanical Check e Verify condition of engine Wide Open Throttle Rich Checks JjAcion Cd DEFINITION Mixture duty cycle readings on the FSA are above 80 and or the oxygen sensor always indicates rich when operating near full throttle Sensor Checks e Check for proper oxygen sensor operation Fuel System Checks e Check for proper primary and secondary regulator pressure validate steady pressure readings at wide open throttle If pressure fluctuates troubleshoot and repair
34. ions the air valve to meter the proper amount of fuel for any given engine speed and load The pressure drop which is controlled by the air valve spring provides the force to draw fuel into the air stream The upward movement of the diaphragm controls the fuel flow in the venturi air valve A pressure drop under the air valve of approximately 0 2 PSI 6 water column of pressure is required to lift the air valve off its seat Approximately 0 5 PSI 13 8 water column lifts the valve to the top of its travel in full open position Lowered pressure communicated to the top of the diaphragm varies with engine speed and position of throttle valve opening The air valve assembly measures the air flow into the engine by moving precisely in response to the demands of the engine and throttle valve position The controlled pressure drop of 0 2 to 0 5 PSI 6 to 13 8 water column set up by the metering spring provides the signal or force necessary to draw fuel into the air stream within the carburetor The gas metering valve is attached to the air valve assembly and is shaped to admit the correct amount of fuel from the gas jet to mix with incoming air at any opening of the air valve ADAPTIVE DIGITAL PROCESSOR ADP The IMPCO Adaptive Digital Processor ADP is an electronic control module designed and manufactured as a closed loop fuel controller for use with gaseous fuel systems It receives input from various engine sensors to compute
35. isconnect the fuel and idle control valve electrical connectors 8 Remove the 4 bolts that attach the two rear support brackets to the main bracket 9 Remove the 2 bolts that retain the converter main bracket to the throttle body adapter 10 Remove the 4 bolts that retain the mixer plate to the throttle body adapter 11 Remove the mixer converter module from the engine 12 Remove the three 3 screws that retain the air inlet adapter to the top of the mixer 13 Remove the air inlet adapter spacer 14 Disconnect and remove the fuel and idle control valves and hoses 15 Remove the four 4 mixer plate screws 16 Unscrew mixer from the converter IMPCO PROPANE FUEL SYSTEM Installation Important e Do not use Teflon tape on any fuel fitting Use a liquid pipe thread sealant when installing fittings Install in reverse order of removal Replace all gaskets during re assembly Tighten fuel fittings finger tight plus 1 to 2 turns Tighten fuel line fittings to 16 20 Ib ft Leak check the system using a liquid leak detector Start vehicle if system does not perform properly perform a fuel system pressure check to verify all system components are operating properly If system pressure check reveals no problems reinitialize the ADP Refer to ADP Initialization in Mechanical Diagnosis OE oie gt ADAPTIVE DIGITAL PROCESSOR ADP Removal 1 Disconnect the negative battery cable 2 Disconn
36. oline fuel supply system e Check for the following Refer to Engine Mechanical in the OEM Service Manual Vacuum leaks Improper valve timing Low compression Bent pushrods Worn rocker arms Broken or weak valve springs Worn camshaft lobes Check the intake and exhaust manifolds for casting flash Refer to Engine Mechanical in the OEM Service Manual Additional Check Check the Idle Air Control IAC operation 1998 GM Medium Duty Chassis Service Manual Supplement Page 8 2 23 98 IMPCO PROPANE FUEL SYSTEM Surges Chuggles Gee Aies DEFINITION The engine has a power variation under a steady throttle or cruise The vehicle feels as if it speeds up and slows down with no change in the accelerator pedal Preliminary Checks Fuel System Checks Ignition System Checks Additional Check 2 23 08 Refer to Important Preliminary Checks Be sure the driver understands the Torque Converter Clutch operation Be sure the driver understands the A C Compressor operation Use the scan tool to make sure the reading of the Vehicle Speed Sensor VSS matches the vehicle speedometer This excludes vehicles with electronic transmissions where some variation between the VSS and the speedometer is normal Check for Rich or Lean symptom that causes the condition Drive the vehicle at the speed of the complaint Monitoring the oxygen sensors will help identify the problem Check the fuel pressure while the condition exists
37. onverter 15 Unscrew the converter assembly 16 Remove the two 2 lock off solenoid mounting bolts 17 Remove the two mounting bolts 18 Remove the converter 19 Transfer all fittings to the new converter from the mixer 2 converter to bracket lock off solenoid from the Installation Important e Do not use Teflon tape on any fuel fitting Use a liquid pipe thread sealant when installing fittings Install in reverse order of removal Replace all gaskets during re assembly Tighten fuel fittings finger tight plus 1 to 2 turns Tighten fuel line fittings to 16 20 lb ft Leak check the system using a liquid leak detector Start the vehicle If the system does not perform properly perform a fuel system pressure check to verify all system components are operating properly If system pressure eg gt 1998 GM Medium Duty Chassis Service Manual Supplement Page 28 2 23 98 check reveals no problems reinitialize the ADP Refer to ADP initialization procedure MIXER Removal 1 Relieve the propane fuel system pressure Refer to Propane Fuel System Pressure Relief 2 Disconnect the negative battery cable 3 Remove air filter assembly cold and hot air ducts 4 Disconnect the fuel supply hose 5 Disconnect the coolant hoses NOTE be sure to relieve cooling system pressure prior to disconnecting the coolant lines 6 Disconnect the electric lock off solenoid electrical connector 7 D
38. pPrOX ie ee Re Ge RA ee ee EE HER N Critical compression ratios a ae aaa a aaaea nnns EE 6 4 1 Best compression ratio range occ ee ee ee ee ee ES LE RE EO N Propane Gasoline 1998 GM Medium Duty Chassis Service Manual Supplement Page 32 2 23 98 Weight per gallon GO ee ee RA Ge AA Re BTU per gallon vaporized BTU per pound vaporized PRESSURE CONVERSION CHART MULTIPLY Inches of Ounces Per Inches of gt Water Square TO OBTAIN v Inches of Water Column Ounces Per Square Inch Inches of Mercury Column Pounds Per Square Inch IMPCO PROPANE FUEL SYSTEM EES ES 4 24H ees OF ERROR 91 500 123 000 EE 21 560 20 500 Pounds Per Square Inch 1998 GM Medium Duty Chassis Service Manual Supplement Page 33 2 23 98
39. stem voltages for the equivalent gasoline operating conditions Peak ignition voltages are experienced during crank and transient conditions a thorough ignition system inspection should be performed e Check for the proper ignition coil output voltage using the spark tester J26792 or the equivalent Check the spark plugs Remove the plugs and inspect them for the following conditions Wet plugs Cracks Wear Improper gap Burned electrodes Heavy deposits Check the ignition system Refer to gnition System Check for crossfire between spark plugs distributor cap spark plug wires and proper routing of the plug wires Engine Mechanical Check Important The propane system works on a fumigation principle of fuel introduction and is more sensitive to intake manifold leakage than a gasoline fuel supply system Check the engine for the following Refer to Engine Mechanical in the OEM Service Manual Improper valve timing Engine compression Manifold vacuum leaks Intake manifold gaskets Sticking or leaking valves Exhaust system leakage Check for an EGR valve that is open all the time Refer to the OEM Service Manual Check the intake and exhaust system for casting flash or other restrictions Refer to Engine Mechanical in the OEM Service Manual Fuel System Checks Perform a fuel system diagnosis Refer to Fuel System Pressure Check Check operation of Idle control valves Check mixer for proper operation sticking wear etc
40. tank to the electric lock off solenoid This solenoid is activated by the fuel pump control circuit The lock off which is normally closed opens only when the engine is cranking or running Fuel passes through the lock off solenoid to the fuel inlet on the converter Propane enters the primary chamber of the converter through the primary jet where the pressure is reduced to 1 2 psi This fuel is then vaporized as it passes through the heat exchanger located in the center of the regulator During normal engine operation the fuel is drawn from the secondary chamber of the regulator by the vacuum created as the air passes through the mixer This pressure drop is most commonly referred to as air valve vacuum As the air valve vacuum increases or decreases the amount of fuel drawn from the secondary chamber will increase or decrease In the mixer the propane vapor is combined with air to form a combustible air fuel mixture The fuel system is controlled by the Adaptive Digital Processor ADP The ADP receives input from various engine sensors to determine the amount of fuel necessary to maintain a precise air propane fuel mixture across the entire engine operational range The ADP then sends a command to the fuel control valve FCV to meter the appropriate quantity of fuel The FCV meters the fuel flow by changing the pressure on the regulator diaphragm from atmosphere to vacuum The system will also automatically sense and compensate
41. tched throttle cable 1998 GM Medium Duty Chassis Service Manual Supplement Page 10 2 23 98 IMPCO PROPANE FUEL SYSTEM Hesitation Sag Stumble Ge Am O DEFINITION The vehicle has a momentary lack of response when depressing the accelerator The condition can occur at any vehicle speed The condition is usually most severe when accelerating after a complete stop The condition may cause the engine to stall if severe enough Preliminary Checks Refer to Important Preliminary Checks Fuel System Checks Ignition System Checks Additional Check 2 23 98 Check the fuel pressure Refer to Fuel System Pressure Test Check for low fuel pressure during a moderate or full throttle acceleration If the fuel pressure drops below specification there is possibly a faulty low pressure regulator or a restriction in the fuel system Check the Throttle Position TP Sensor for binding or sticking Voltage should increase at a steady rate as the throttle moves toward Wide Open Throttle WOT Check the Manifold Absolute Pressure MAP sensor response and accuracy Check the mixer and adapter assembly for proper installation and leakage Check the mixer for proper operation sticking wear etc Check for sticking fuel control or idle control valve Note LPG being a gaseous fuel requires higher secondary ignition system voltages for the equivalent gasoline operating conditions Peak ignition voltages are experienced dur
42. ter Clutch TCC operation Refer to Torque Converter Clutch Solenoid in Automatic Transmission Check for proper calibration of the speedometer Check for dragging brakes Refer to Section 5 of the appropriate service manual 1998 GM Medium Duty Chassis Service Manual Supplement Page 15 IMPCO PROPANE FUEL SYSTEM Rough Unstable or Incorrect Idle Stalling wd a DEFINITION The engine runs unevenly at idle If severe enough the engine or vehicle may shake The engine idle speed may vary in RPM Either condition may be severe enough to stall the engine Preliminary Check e Refer to Important Preliminary Checks Sensor Checks e Check the Heated Oxygen Sensor HO2S performance e Check for silicon contamination from fuel or improperly used sealant The sensor will have a white powdery coating The sensor will result in a high but false signal voltage rich exhaust indication The control Module will reduce the amount of fuel delivered to the engine causing a severe driveability problem Check the Engine Coolant Temperature ECT sensor using the scan tool to compare the engine coolant temperature with the ambient air temperature on a cold engine If the coolant temperature reading is more than 5 greater than or less than the ambient air temperature on a cold engine check for a high resistance in the coolant sensor circuit or the sensor itself Check the Manifold Absolute Pressure MAP sensor response and accuracy
43. the assembly The removal of the secondary fulcrum pin releases the spring and lever assembly Note the three retaining pins on the underside of the lever above the index finger These are used to locate the spring Remove the primary diaphragm cover C1 20 This requires the removal of four Phillips head screws and two pan head screws The C1 20 cover removal releases two S2 13 primary springs and the primary diaphragm assembly Remove the primary diaphragm assembly AD1 15 and the primary valve pin P1 11 The primary valve is actuated by this pin through the body This isolates the diaphragm from any contact with liquid propane Remove the last two S1 39 screws Remove the body B1 20 from the heat exchanger AB1 19 After the B1 20 body is removed remove the body gasket G1 37 and sponge F3 1 The purpose of the sponge is to absorb liquid propane on cold starts then retain the liquid until it vaporizes Remove the primary valve seat S4 7 and discard The high pressure jet is case hardened steel and is pressed in place Remove the back cover C1 21 of the heat exchanger This requires the removal of six S1 3 back cover Screws Tap the side of the cover firmly with a plastic handle to break the cover loose from the gasket Remove the back cover gasket G1 35 The ribs on the underside of the cover support the back gasket while providing air gaps for expansion in case of a water freeze up Thoroughly
44. too often e Suggest to the owner to fill the fuel tank and to recheck the fuel economy e Suggest to the driver to refer to Important Facts on Fuel Economy in the owner s manual Sensor Checks e Check the Engine Coolant Temperature ECT sensor with the scan tool Compare the engine coolant temperature with the ambient air temperature on a cold engine IF the coolant temperature reading is more than 5 degrees greater or less than the ambient air temperature on a cold engine check for high resistance in the coolant sensor circuit e Check the Manifold Absolute Pressure MAP sensor e Check the Heated Exhaust Gas Oxygen HEGO sensor Ignition System Checks e Check the spark plugs Remove the plugs and inspect them for the following conditions Wet plugs Cracks Wear Improper gap Burned electrodes Heavy deposits e Check for an open Ignition Control IC circuit e Check the ignition wires for the following items Cracking Hardness Proper connections e Check the Knock Sensor KS system 1998 GM Medium Duty Chassis Service Manual Supplement Page 14 2 23 98 Cooling System Checks Additional Check 2 23 98 IMPCO PROPANE FUEL SYSTEM Check the engine coolant level Check the engine thermostat for always being open or for the wrong heat range Refer to Diagnosis of the Thermostat in Engine Cooling Check the transmission shift pattern Refer to the Transmission Controls section Check for Torque Conver
45. uel control valve FCV signal yellow wire 3 Start the engine and allow it to reach normal operating temperature 4 During warm up monitor the following e OnaFSA the reading should start at 0 and increase until the oxygen sensor output begins to switch from rich to lean On a dwell meter the reading should maintain an average 30 dwell e Once the reading stabilizes on the FSA the duty cycle should maintain a tight range and the rich and lean lights should cycle on and off Important e Do not turn the engine off before re installing connector P14 or the ADP block learn memory will not be updated 5 When the engine is at normal operating temperature and the FSA or the dwell meter shows continuos rich lean cycling re connect connector P14 and disconnect the tool 6 To update block learn memory the vehicle should be driven for approximately five minutes under the following conditions 1st Steady state cruise 2nd Light throttle 3rd Medium throttle 4th Heavy throttle When the drive cycle is completed return the vehicle to service 1998 GM Medium Duty Chassis Service Manual Supplement Page 24 2 23 98 IMPCO PROPANE FUEL SYSTEM IMPCO PROM the underhood label If necessary reset the timing to match those specifications Check the OEM data stream using a scan tool If no data stream is available refer to the OEM Important service manual for proper diagnostic procedures e Installing the wrong PROM in t
46. ut off valve is open and that the excess flow valve has not closed Check the propane fuel filter and replace if necessary Verify primary and secondary lock off operation Check fuel lines for kinks or restrictions frost or condensation may be present if restricted Repair As Was a problem found SES Go to Step 5 Regulator pressure is out of range Repair or replace regulator Repeat the regulator pressure test to verify repair Go to Step 6 Is the action complete Fuel supply system operating normally Ha driveability complaint persists refer to diagnostic by symptom table Go to the Applicable System OK Are any DTCs or driveability symptoms present DTC Table 1998 GM Medium Duty Chassis Service Manual Supplement Page 20 2 23 98 IMPCO PROPANE FUEL SYSTEM MECHANICAL DIAGNOSIS CONVERTER TROUBLESHOOTING CHART CONDITION CAUSE CORRECTION INSUFFICIENT FUEL Insufficient fuel supply or Check fuel supply and electric lock off solenoid FLOW defective electric lock off Repair as necessary solenoid Incorrect secondary spring Verify proper spring for application installed Incorrect secondary lever Adjust lever height using G2 2 gauge or height appropriate repair instructions Secondary chamber full of Disassemble and inspect regulator oil or contaminants Primary pin sticking in bore Disassemble and inspect regulator Secondary diaphragm Replace regulator secondary diaphragm damaged Primary ori
47. ve the propane fuel system pressure Refer to Propane Fuel System Pressure Relief 2 Disconnect the negative battery cable 3 Remove the air cleaner 4 Disconnect the vacuum hose from the regulator control valve RCV 5 Unscrew the RCV from the converter Installation Important e Do not use Teflon tape on any fuel fitting Use a liquid pipe thread sealant when installing fittings 1 Apply liquid pipe thread sealant to the RCV threads 2 Install in reverse order of removal CONVERTER Removal 1 Relieve the propane fuel system pressure Refer to Propane Fuel System Pressure Relief Disconnect the negative battery cable Disconnect the hot and cold air ducts Remove the air cleaner Disconnect the fuel supply hose Disconnect the coolant hoses NOTE Relieve cooling system pressure before disconnecting the coolant lines DPPN 7 Disconnect the electric lock off solenoid electrical connector 8 Disconnect the fuel and idle control valve electrical connectors 9 Remove the four 4 bolts that attach the two rear support brackets to the main bracket 10 Remove the two 2 bolts that retain the converter main bracket to the throttle body adapter 11 Remove the four 4 bolts that retain the mixer plate to the throttle body adapter 12 Remove the mixer converter module from the engine 13 Disconnect the RCV hose and remove the RCV 14 Disconnect the fuel control valve vacuum hose from the c
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