fuel system - Central States Bus Sales, Inc.
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1. moisture collection trap s are equipped L Warning Light 2 Red Wi with electric heater elements to prevent accumulated water from freezing The mois to 412VDC i Black Wire ture trap may also be equipped with an electric water sensor which causes a yellow Optional from light Water Level to 12VDC warning light in the Driver s instrument panel to illuminate when water in the trap Sensor rises to a level sufficient to complete the circuit between the sensor s contacts This indicates it is time to drain the contaminant collection bowl After the water has been 596 drained from the bowl the yellow warning light resets On All Americans equipped with Cummins ISB engines the primary filter is a Ray cor filter water separator unit with a replaceable spin on element The Raycor filter incorporates a see through trap bowl which is equipped with a manually operated drain and electric heater The secondary filter is a Fleetguard unit mounted to the engine and equipped with water separation feature a manual operated water drain electric heater and electric moisture sensor Consult the engine manufacturer s Operators Manual supplied with the bus re garding maintenance schedules and replacement cartridges for the secondary filter Blue Bird recommends using only OEM replacement filter elements 0 BLUE BIRD FUEL SYSTEM Fuel Delivery On Cummins engines two pumps are employed The transfer pump draws fuel from2. to raise engine RPM above idle This condition is normal dur ing the power up and auto calibration period Pulse Width Modulation Several components on the Blue Bird All Americam employs pulse width modulation rather than mechanical rheostats or resistors These include the acellerator pedal and instrument lighting This illustration explains the basic principle of Pulse Width Modulation 601 Uniform Square Waveform WAVELENGTH WAVELENGTH WAVELENGTH In this unmodulated wave Wavelength and therefore Frequency is constant Amplitude wave height is constant Pulse Width the positive portion of the wave is constant Note that in this example the Pulse Width occupies 50 of the total wavelength PULSEWIDTH PULSEWIDTH PULSEWIDTH 50 50 50 50 50 50 Pulse Width Modulation PWM WAVELENGTH WAVELENGTH WAVELENGTH In a PWM circuit information is conveyed by varying the percentage of total wavelength which is occupied by the Pulse Width Wavelength therefore Frequency is constant Amplitude is constant Pulse Width varies Note that now the Pulse Width varies PULSEWIDTH PULSEWIDTH lt PULSEWIDTH independently of Wavelength The Pulse Width to Wavelength ratio is expressed as a percentage and is referred 20 pro CS 40 pura 60 DUTY CYCLE to as Duty Cycle BLUE BIRD D3 FE SERVICE MANUAL Accelerator Testing And Troubleshooting The Cummins accelerator pedal incorporates two Throttl
3. 597 If both filters and fuel system components external to the engine package have been eliminated as causes but a fuel related problem is still suspected consult the engine manufacturer s service documentation for troubleshooting procedures Fuel Supply Line Fuel Return Line 0 BLUE BIRD SERVICE MANUAL 598 Magnobond Should Be Applied To Insure Acomplete Airtight Seal Typ 6 Flanges Fuel Tank amp Barrier 0 FUEL SYSTEM Fuse Tank Vent Fuse 3 ee 100 Gallon N Tank ball N N Drain Plug Fill Vent 60 gal only See tank detail for 100 gal fitting placment Fuel Sender Not Used Supply Fuse Fuse _ Plug Fuse 60 Gallon Tank M aJ N Drain Tanevent Fill Vent Fuel Sender Not Used Supply Typical routing of hoses Return Through crossmembers gt gt 9 A 4 Y AY 4 Y y y 4 Y A y 4 4 4 A amp QB Re BW Q e ky o To fuel ae ewe port on engine To fuel supply port on engine CUMMINS ISB 07 Fuel System Diagram 599 BLUE BIRD SERVICE MANUAL 0 BLUE BIRD Accelerator Control Electronic The All American s throttle control regulates engine speed not by direct mechani cal linkage but by electronically communicating the position of the pedal to the engine s Electronic Control Module ECM The ECM in turn controls the engine s fuel system to adjust engine spee
4. FUEL SYSTEM Fuel System Fuel Storage On most All American buses the fuel tank is mounted between the frame rails and is surrounded for impact protection by a barrier system of steel panels and structural beams On All American Forward Engine the between rails fuel tank is located in the rear overhang aft of the rear axle Some All American Forward Engine buses have fuel tanks mounted outboard of the frame rails on the right side of the bus Fuel tanks of several capacities are available All are rectangular tanks secured by a set of steel straps which surround the tank and mount to the barrier and sup port members All tube fittings filler necks and sending units are mounted on the top of the fuel tank An inspection port on the floor of the passenger compartment provides access to the fuel sending unit Filler Neck Fitting Supply Fitting Fuel Sender Fill Vent Supply Fitting Filler Neck Fitting Fuel Sender QE QUEGINING Blue Bird Product Engineering does not approve or disapprove additions to or modi fications of Blue Bird fuel sys tems Blue Bird fuel systems are designed and installed to meet federal standards and engine manufacturer s guidelines The upfitter or modifier assumes all responsibility for vehicle engine and fuel system if the fuel system is modified In 2007 diesel en gines use only diesel fuel labeled Ultra Low Sulfur per the engine manufacturer s specifications In Cum
5. d When the pedal is pressed its lever arm rotates a spring loaded mechanism in side the throttle assembly s housing Attached to the side of the housing is an elec tronic position sensor which varies a signal it sends to the engine ECM The signal modulates according to the position of the rotating part of the pedal assembly The accelerator pedal assembly is mounted entirely inside the bus with no part of it extending through the firewall The assembly is not rebuildable therefore it must be replaced as a unit if damaged or faulty The Accelerator Pedal Position Sen sor APPS requires no adjustment and is not rebuildable However it is replaceable as a separate unit from the pedal assembly Throttle Position Sensor The APPS receives an 8 volt DC supply voltage from the engine ECM drawing less than 40mA of current It s electonic circuitry senses the accelerator pedal position and generates an output signal which communicates the throttle position back to the ECM The output signal conveys its data by means of pulse width modulation PMW a method by which the wave form of a pulsating DC current signal may be altered in order to convey a signal Because of its fundamentally on off nature square wave form PWM is particularly well suited for communication between digital control de vices and microprocessors Pulse Width Modulation Pulse width modulation varies the width of the positive crest of each wave of cur rent Thus in pul
6. e Position Sensors to pro vide the required input to the engine ECM These components are non serviceable and should not be removed from the accelerator assembly or you could risk voiding the warranty Each component has three wires going through a weather pak con nector and can be tested individually for proper operation Throttle Position Sensor Coil Resistance The Throttle Position Sensor provides the engine an analog signal instructing it to increase or decrease RPM based on the position of the accelerator This is done with a three wire potentiometer The sensor is provided a continuous 5V DC pin B27 and a ground pin B28 by the engine ECU As the accelerator pedal is depressed the throttle position sensor will relay its position to the engine pin B35 The throttle position sensor can be tested by the following Disconnect sensor plug and meassure resistance on accelerator side of connec tor between e Pins Cand A Supply and Return Value should be between 2000 and 3000 ohms 602 e Pins C and B Supply and Return Released pedal value should be between 1500 and 3000 ohms e Pins C and B Supply and Return Depressed pedal value should be between 200 and 1500 ohms Resistance should decrease proportionally as pedal is depressed Released pedal resistance minus depressed pedal resistancemust be greater than 1000 ohms ATID Do not attempt to adjust or repair throttle position sensor or idle validation sensor Warranty wil
7. l be voided Should the accelerator fail to meet specifications the entire pedal must be re placed CUMMINS ISB 07 ECM THROTTLE POSITION RETURN THROTTLE POSITION SIGNAL 1 5V THROTTLE POWER ECM RETURN SENSOR THROTTLE POSITION SIGNAL 2 ECM SENSOR SUPPLY 5VDC Twisted Circuits BLUE BIRD Accelerator Pedal Assembly THROTTLE POSITION SENSOR 1 THROTTLE POSITION SENSOR 2
8. mins use oils meeting API CJ 4 SL and Cummins Engine Standard CES 20081 See Cum mins Owners Manual ISB 6 7L CM2150 for details 595 0 BLUE BIRD SERVICE MANUAL Fuel Filtration It is critical to the high pressure fuel injection systems of modern diesel engines that fuel is free of contaminates and moisture Diesel fuel serves to lubricate the injector pumps any water in the fuel inhibits that lubrication and can lead to in jector pump failure Therefore dilligent inspection and maintenance of the fuel system filters is essential to engine longevity and performance Diesel fueled All Americans are equipped with two stages of fuel filtration a Bivins primary filter and a secondary filter each with its own replaceable element The primary filter is mounted by Blue Bird between the tank and the engine along the inside of the left frame rail and provides the first stage of filtration at a scale of Collection Bowl Water Probe Port approximately 10 microns The second stage of filtration is provided by a much finer filter 2 5 microns depending upon specific engine mounted on the engine N Probe Assembly by the engine manufacturer Water separation occurs at either or both filters de amp Connector BlackWire_ E Yellow Wire to me ee to light pending upon which engine is installed A manually operated drain is provided to allow collected moisture to be expelled The
9. se width modulation both the voltage amplitude and wave length frequency remain constant while the duration of the positive pulse pulse width varies The longer the duration of the pulse the higher the percentage of the total wave length it occupies For this reason pulse width is measured as a percentage of the wavelength The percentage is refered to as the duty cycle In typical applications the signal frequency is quite higher than the response rate of the load device The on off pulses therefore tend to be smoothed out or averaged over time while the load operates The net result is the appearance and be havior of varying output voltage even though the voltage of the pulses is constant FUEL SYSTEM Auto Calibration The ECM is programmed to automatically re calibrate its responses to the throttle position sensor signal each time the ignition is turned on Initially the ECM interprets a 22 pulse wave as a call for low idle and a 75 pulse wave as full RPM During the normal use cycling of the accelerator pedal the ECM adjusts its calibration resulting in a broader duty cycle range in which 10 22 signals idle and 75 90 signals full RPM This process results in a slight but noticable change in the throttle pedal s sensi tivity until the auto calibration is completed During this time the Driver may notice that full RPM is achieved before the pedal is fully depressed and or that more pedal movement is required
10. the tank through the frame mounted Raycor filter and into the engine sup ply port The fuel then passes through a cooling coil mounted between the engine ECM and the engine Thus fuel is used as a cooling agent to reduce the temperature of the Electronic Control Unit Leaving the ECM cooler the fuel passes through the engine mounted secondary filter and then enters a second high pressure pump The high pressure pump delivers the fuel under increased pressure to the Cummins Com mon Rail fuel delivery system The portion of the fuel flow not used by the injectors continues on its way back to the engine s fuel return port where a 1 2 OD fuel line conveys it back toward and into the top of the fuel tank Fuel system delivery problems typically manifest themselves as symptoms such as failure to start rough idling rough running etc When a fuel related problem is suspected first check the Driver s dash panel warning lights for any light which would be generated by the ECM Check Engine Stop Engine etc If any such lights are displayed use the engine manufacturer s recommended electronic diagnostic tool s to obtain more detailed information about any stored error codes If no dash light errors are indicated check the fuel delivery system components between the fuel tank and the engine s supply and return ports for possible causes such as clogged filters water presence in the water separator bowl leaking or other wise damaged lines etc
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