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ELECTRONIC ENGINE CONTROL GM V-6 4.3L DESCRIPTION AND OPERATION H3.50-5.50XM (H70-120XM) [K005] PART NO. 1467758 2200 SRM 766

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  • ELECTRONIC ENGINECONTROL

    GM V-6 4.3LDESCRIPTION AND OPERATION

    H3.50-5.50XM (H70-120XM) [K005]

    PART NO. 1467758 2200 SRM 766

  • SAFETY PRECAUTIONSMAINTENANCE AND REPAIR

    When lifting parts or assemblies, make sure all slings, chains, or cables are correctlyfastened, and that the load being lifted is balanced. Make sure the crane, cables, andchains have the capacity to support the weight of the load.

    Do not lift heavy parts by hand, use a lifting mechanism.

    Wear safety glasses.

    DISCONNECT THE BATTERY CONNECTOR before doing any maintenance or repairon electric lift trucks.

    Disconnect the battery ground cable on internal combustion lift trucks.

    Always use correct blocks to prevent the unit from rolling or falling. See HOW TO PUTTHE LIFT TRUCK ON BLOCKS in the Operating Manual or the Periodic Mainte-nance section.

    Keep the unit clean and the working area clean and orderly.

    Use the correct tools for the job.

    Keep the tools clean and in good condition.

    Always use HYSTER APPROVED parts when making repairs. Replacement partsmust meet or exceed the specifications of the original equipment manufacturer.

    Make sure all nuts, bolts, snap rings, and other fastening devices are removed beforeusing force to remove parts.

    Always fasten a DO NOT OPERATE tag to the controls of the unit when making repairs,or if the unit needs repairs.

    Be sure to follow the WARNING and CAUTION notes in the instructions.

    Gasoline, Liquid Petroleum Gas (LPG), Compressed Natural Gas (CNG), and Diesel fuelare flammable. Be sure to follow the necessary safety precautions when handling thesefuels and when working on these fuel systems.

    Batteries generate flammable gas when they are being charged. Keep fire and sparksaway from the area. Make sure the area is well ventilated.

    NOTE: The following symbols and words indicate safety information in thismanual:

    WARNINGIndicates a condition that can cause immediate death or injury!

    CAUTIONIndicates a condition that can cause property damage!

  • Electronic Engine Control Table of Contents

    TABLE OF CONTENTS

    General ............................................................................................................................................................... 1Description and Operation ................................................................................................................................ 1

    General ........................................................................................................................................................... 1ECM (Electronic Control Module) ................................................................................................................ 1

    Diagnostic Connector ................................................................................................................................ 1How ECM Begins Operation..................................................................................................................... 3

    Electronic Engine Control ............................................................................................................................. 3What ECM Does ........................................................................................................................................ 3Pulse Generator, EST Distributor ............................................................................................................ 5EST Module ............................................................................................................................................... 5When Engine is Being Started ................................................................................................................. 6When Engine is Running .......................................................................................................................... 7Electronic Control Module (ECM) With EST Distributor, Corrections .................................................. 7

    Fuel Control ................................................................................................................................................... 8Injection Throttle Body ................................................................................................................................. 9

    Fuel Injectors............................................................................................................................................. 9Fuel Pressure Regulator ........................................................................................................................... 9

    Governor Throttle Body Assembly................................................................................................................ 10Throttle Position Sensor (TPS)................................................................................................................. 11Idle Air Control.......................................................................................................................................... 11Vacuum Ports............................................................................................................................................. 12Fuel Pump ................................................................................................................................................. 12

    ECM Sensors and Controllers....................................................................................................................... 13Manifold Absolute Pressure (MAP).......................................................................................................... 13Coolant Temperature Sensor (CTS) ......................................................................................................... 13

    This section is for the following models:

    H3.50-5.50XM (H70-120XM) [K005]

    2002 HYSTER COMPANY i

  • "THEQUALITYKEEPERS"

    HYSTERAPPROVEDPARTS

  • 2200 SRM 766 Description and Operation

    GeneralNOTE: Engines that have an LPG fuel system usethe carbureted engine management system (CEMS).They do not have an electronically controlled fuel in-jection system.

    This section has the description and operation of theelectronic engine control system and the componentsin that system. The repair and troubleshooting pro-cedures for the system used in the GM V-6 engineis in the section Electronic Engine Control Trou-bleshooting and Repair 2200 SRM 767.

    Description and OperationGENERALWhen a carburetor and distributor are used for fuelsupply and ignition control, a single adjustment can-not be made to give the best adjustment for all oper-ating speeds and conditions. The use of microproces-sors has enabled the development of electronic sys-tems that can better control engines that use gaso-line or liquid petroleum gas (LPG) during all operat-ing conditions.

    An electronic engine control continuously makes ad-justments to control the spark timing and fuel mix-ture to the engine. This control gives the followingbenefits: Engine is easier to start and operate during chang-

    ing conditions. Approximately 15% better use of fuel. Reduction of some exhaust gases that can create

    a hazard (carbon monoxide is reduced approxi-mately 80%, hydrocarbons are reduced approxi-mately 50%).

    An electronic governor is installed for finer enginespeed control.

    Electronic monitoring of engine operation as an aidto troubleshooting.

    ECM (ELECTRONIC CONTROL MODULE)The ECM (Figure 1) is a small computer that con-trols the ignition timing and fuel supply in a gasolineengine. An Electronically Erasable ProgrammableRead Only Memory (EEPROM) is installed in theECM. This EEPROM is programmed with informa-tion for the best operation of the engine accordingto the fuel, temperature, load, and other conditions.The ECM receives signals from sensors on the en-gine, and electronically controls the following sys-tems and components for the best fuel use and engineperformance: A fuel injection system.

    Electronic spark timing (EST). An electronic governor. Check engine light. Idle air control (IAC). Fuel pump relay. A serial data link for troubleshooting.

    1. ECM2. J1 CONNECTOR3. J2 CONNECTOR

    Figure 1. ECM

    Each ECM has a specific program for the model oflift truck in which it is installed. A replacementECM must have the same part number so that thelift truck will operate correctly.

    Diagnostic ConnectorThe diagnostic connector is connected through awiring harness to the ECM. The connector is animportant link for troubleshooting the operation ofthe ECM and the electronic engine control system.The diagnostic connector is found in the engine com-partment. See Figure 2. The use of the diagnosticconnector is described in the Electronic EngineControl Troubleshooting and Repairs 2200SRM 767 section for these engines.

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  • Description and Operation 2200 SRM 766

    A. TOP VIEW B. VIEW FROM TRANSMISSION

    1. COOLANT TEMPERATURE SENSOR (CTS)2. FUEL PUMP RELAY3. ELECTRONIC CONTROL MODULE (ECM)4. DIAGNOSTIC CONNECTOR MATING

    CONNECTOR5. FUEL FILTER6. THROTTLE POSITION SENSOR (TPS)7. GOVERNOR CONTROL MODULE8. MANIFOLD ABSOLUTE PRESSURE (MAP)

    SENSOR

    9. IGNITION COIL10. EST DISTRIBUTOR11. OIL PRESSURE SENDER12. FUEL PRESSURE REGULATOR13. FUEL STACK14. FUEL INJECTORS15. IDLE AIR CONTROL (IAC) VALVE16. WATER TEMPERATURE SENDER

    Figure 2. GM 4.3 L V-6 Engine, Electronic Engine Control, Components Arrangement

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  • 2200 SRM 766 Description and Operation

    Figure 3. Electronic Engine Control System

    How ECM Begins OperationWhen the ignition switch is turned to ON, the ECMdoes the following functions (see Figure 3): Measures the atmospheric pressure (BARO signal)

    from the MAP sensor. Checks the signal from the coolant temperature

    sensor (CTS). Energizes the fuel pump relay for approximately

    2 seconds. Checks that the throttle position sensor (TPS) in-

    dicates that the throttle is less than 80% open. Ifthe throttle is more than 80% open, the ECM willdetermine that the engine is flooded with fuel andwill deliver less fuel to the engine.

    Electronic Spark Timing (EST) DistributorSystem: The EST system checks the startingmode from the EST module. When the starter isengaged, the EST module sends electronic pulsesto the ECM. The frequency of the pulses indicatesto the ECM that the engine is being started. TheEST module also electronically energizes (ON)and de-energizes (OFF) the primary circuit of theignition coil to create a spark at the spark plugs.

    The ECM makes the checks in a few milliseconds anddetermines the correct air and fuel ratio for startingthe engine. The range of this air and fuel ratio is1.8:1 at 40 C ( 40 F) to 17:1 at 150 C (302 F) asindicated by the signal from the coolant temperaturesensor. The ECM controls the amount of fuel sentto the engine by changing the pulse times [how longthe fuel injector is energized (ON) and de-energized(OFF)].

    When the engine starts, the frequency of the pulsesfrom the EST module increases and indicates to theECM that the engine is running. The ECM takes con-trol of the ignition timing, and the EEPROM withinthe ECM follows its program to give ignition tim-ing and fuel control for the best engine operation.When the engine is operating, the ECM continuouslychecks the signals from the MAP, CTS, and TPS tomake timing and fuel adjustments for the engine op-erating conditions.

    ELECTRONIC ENGINE CONTROL

    What ECM DoesThe ECM receives signals from the following compo-nents (see Figure 4): Manifold Absolute Pressure Sensor (MAP).

    This sensor is a pressure transducer that mea-sures the atmospheric pressure before the engineis started and the ECM uses this pressure as areference. This sensor then measures changesin pressure in the intake manifold during engineoperation.

    Coolant Temperature Sensor (CTS). This sen-sor is a thermistor (resistor that is calibrated tochange its value as its temperature changes) thatmonitors the engine coolant temperature.

    Throttle Position Sensor (TPS). This sensor in-dicates the position of the throttle that is set by theoperator and is used with the indications from theother sensors to determine the correct engine oper-ation.

    Fuel Pump. When the key switch is first turnedto ON, the ECM energizes the fuel pump relayfor 2 seconds. This action quickly raises the fuel

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  • Description and Operation 2200 SRM 766

    pressure to the fuel injectors. If the engine is notcranked or started within 2 seconds, the ECMde-energizes the fuel pump relay and the fuelpump goes to OFF. When the engine is crankedby the starter, the ECM energizes the fuel pumprelay again so that the fuel pump operates.

    EST module. This component is a small electronicmodule within the distributor. See Figure 5. ThisEST module is a signal converter that senses theoperation of the distributor. A sensor coil in thedistributor senses the rotation of the timer coreand the EST module senses the speed of rotation.A square wave generator in the EST module con-verts the pulses from the sensor coil to a squarewave signal that is sent to the ECM. If the sig-nals from the EST module to the ECM indicatethat the crankshaft is rotating at less than 400rpm, the ECM determines that the engine is be-ing cranked by the starter. The EST module con-trols the ignition for an engine being started. The

    Electronic Spark Timing (EST) function from theECM is de-energized. If the signals from the ESTmodule to the ECM indicate that the crankshaftis rotating at greater than 400 rpm, the ECM de-termines that the engine is running and the Elec-tronic Spark Timing (EST) controls the ignition.

    Electronic Governor. The ECM senses the en-gine speed from the EST module and operates thegovernor motor on the throttle body to control theengine speed. The governor motor will override thethrottle position that is set by the operator to con-trol the engine speed within the limits set in theECM. The operation of the governor is describedlater in this section under Governor Throttle BodyAssembly.

    Figure 4. Electronic Engine Control with EST Distributor

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  • 2200 SRM 766 Description and Operation

    Legend for Figure 4

    1. ELECTRONIC CONTROL MODULE (ECM)2. THROTTLE POSITION SENSOR3. COOLANT TEMPERATURE SENSOR (CTS)4. MANIFOLD ABSOLUTE PRESSURE SENSOR

    (MAP)5. FUEL PUMP RELAY6. FUEL PUMP

    7. FUEL INJECTOR (2)8. GOVERNOR MOTOR9. CONTROLLER, GOVERNOR MOTOR10. DISTRIBUTOR11. SPARK PLUG (6)12. IGNITION COIL

    Pulse Generator, EST DistributorA timer core on the shaft of the distributor has ex-ternal teeth which align with an equal number ofteeth on the pole piece of the permanent magnet. SeeFigure 5. When the teeth of the timer core rotatepast the teeth of the pole piece, there is a decreasein the air gap between the timer core and the polepiece. The magnetic field increases. When teeth arenot aligned, the magnetic field decreases between thetimer core and the pole piece. As the timer core ro-tates, the magnetic field increases and decreases ina cycle.

    When a coil is near a changing magnetic field, a volt-age is generated in the coil. This principle is calledmagnetic induction. A sensing coil is installed overthe permanent magnet. As the magnetic field nearthe pole piece changes, a small voltage is generatedin the sensing coil.

    The principle of magnetic induction also controls thepolarity of the voltage generated in the coil. An in-creasing magnetic field will generate a voltage in thecoil that is the opposite polarity of a magnetic fieldthat is decreasing. This signal pulse causes the in-tegrated circuits in the EST module to generate asquare wave signal. The EST module and a mag-netic pulse generator control the primary circuit tothe ignition coil when the engine is started. The ECMreceives the square wave signal from the magneticpulse generator and EST module as one of the sig-nals to control the EST. The pole piece has the samenumber of teeth as the engine has cylinders so that aspark voltage is correctly sent to each spark plug asthe shaft in the distributor rotates.

    EST ModuleThe EST module is a solid-state electronic device thatoperates like a fast switch, except that it does nothave any moving or mechanical parts. See Figure 6.Small electrical pulses from the sensing coil of thepulse generator go to the EST module.

    1. CAP2. ROTOR3. SHAFT/TIMER4. RETAINER5. SHIELD6. COIL7. POLE PIECE8. EST MODULE

    9. ALIGNMENT PIN10. HOUSING11. WASHER12. SEAL13. DRIVE GEAR14. ROLL PIN15. GASKET

    Figure 5. EST Distributor Parts

    The ECM must always know the speed at which theengine is operating. The engine speed signal is gen-erated by the EST module. The square wave gener-ator (3) changes the signal voltage from the sensingcoil to a square wave reference signal to the ECM.This square wave reference signal for engine speedis called REF HI. The ECM must also have a refer-ence to compare with REF HI. An additional wire be-tween the ECM and the EST module is called REFLO (ground). The REF HI and REF LO connectionspass data about engine speed to the EEPROM in theECM.

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  • Description and Operation 2200 SRM 766

    The other two wires between the ECM and the dis-tributor control the Electronic Spark Timing and arecalled EST and BYPASS.

    NOTE: The EST module controls spark timing onlywhen the engine is being started or if the ECM fails.The ECM controls the spark timing during engine op-eration. The EST module will also control the sparktiming if there are some failures in the signals to theECM. This backup mode of operation will often per-mit operation of the engine so that the lift truck canbe moved to an area for repair. The result of failuresin signals to the ECM is described in the paragraphsunder Electronic Control Module (ECM) With ESTDistributor, Corrections.

    When Engine is Being StartedWhen the engine is cranked by the starter, the elec-tronic relay (2) is in the de-energized position. The

    sensing coil is connected through the square wavegenerator (3) to the base of the transistor (8). SeeFigure 6.

    When the sensing coil (4) applies a positive voltage(the square wave voltage is increasing) to the tran-sistor (8), the transistor goes ON. When the voltagefrom the sensing coil changes to negative (the squarewave voltage is decreasing), the transistor goes OFF.When the transistor is ON, current flows through theprimary winding of the ignition coil. When the tran-sistor goes OFF, the current flow through the pri-mary winding stops. The changing magnetic field inthe primary winding generates a high voltage in thesecondary winding of the ignition coil. This high volt-age generates a spark at the spark plug.

    1. EST MODULE2. ELECTRONIC RELAY3. SQUARE WAVE GENERATOR4. SENSING COIL

    5. ELECTRONIC CONTROL MODULE (ECM)6. BATTERY (+) TO COIL7. TO IGNITION COIL ( )8. TRANSISTOR

    Figure 6. EST Module When Engine is Being Started

    6

  • 2200 SRM 766 Description and Operation

    When Engine is RunningWhen the engine speed is greater than approx-imately 400 rpm, the ECM determines that theengine is running and applies 5 volts on the BYPASSwire to the EST module (see Figure 7). This voltageenergizes the electronic relay (2) and makes thefollowing changes: The EST wire is not grounded

    and is now connected to the base of the transistor(8). The sensing coil (4) is disconnected from thebase of the transistor (8).

    The EST module and the ignition timing is now con-trolled by the EST signal from the ECM. This modeof operation is called the EST mode.

    1. EST MODULE2. ELECTRONIC RELAY3. SQUARE WAVE GENERATOR4. SENSING COIL

    5. ELECTRONIC CONTROL MODULE (ECM)6. BATTERY (+) TO COIL7. TO IGNITION COIL ( )8. TRANSISTOR

    Figure 7. EST Module When Engine is Running

    Electronic Control Module (ECM) With ESTDistributor, CorrectionsThe operation of the ECM was described in earlierparagraphs (see the description in What ECM Does).These paragraphs describe the corrections made bythe ECM in an engine with an EST distributor.

    The ECM does a check of the system components ofthe EST. A set of normal operating limits is part ofthe EEPROM program. If a sensor sends a signalthat is outside of the limits of the EEPROM program,the ECM will not use the information. The ECM willuse a standard value from its program and continueto operate the EST.

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  • Description and Operation 2200 SRM 766

    The following examples are the action of the ECM ifit detects a problem:

    MAP Sensor Signal Voltage Is Too High OrToo Low. The ECM will use a MAP value from itsEEPROM program and use this value to calculatethe ignition timing.CTS Signal Voltage Is Too High Or Too Low.If the coolant sensor sends a signal voltage that isoutside of the range programmed by the ECM, theECM will determine that the engine is cold. TheECM will use a value for a cold engine.Open Circuit In EST Wire. Normally, the signalfrom the ECM to the EST module rises and falls asthe voltage from the sensing coil rises and falls. Ifthe EST circuit is open, the electronic relay in theEST module is not at ground potential. The enginewill start but will not continue to run. If the ESTcircuit becomes open during engine operation, theengine stopsShort Circuit (Grounded Circuit) In ESTWire. When the engine is being rotated by thestarter, the ECM normally detects zero volts inthe EST circuit because the circuit is at groundpotential in the HEI module. The ECM would notdetect a problem until the engine began to run.The ECM could not operate in the EST mode andthe engine will not operate. If the EST circuit hasa short circuit (grounded circuit) when the engineis running, the engine stops.Open Circuit Or Short Circuit In The BY-PASS Circuit. The ECM would not detect aproblem until the engine began to run. The ECMcould not operate in the EST mode and the enginewould operate with reduced power. If this problemoccurs when the engine is running, the enginewill only operate in the starting mode with theHEI module.Open Circuit Or Short Circuit In The REFHI Circuit. The ECM would not detect that theengine was operating. The ECM could not operatein the EST mode and the engine will not operate.Open Circuit Or Short Circuit In The REFLO Circuit. The ECM would not have a compar-ison for operation. The ECM could not operate inthe EST mode and the engine will not operate cor-rectly.

    FUEL CONTROLThe components of the fuel system are shown in Fig-ure 8.

    1. ADAPTER2. GASKET3. INJECTOR THROTTLE BODY4. FUEL PRESSURE REGULATOR5. GASKET6. THROTTLE POSITION SENSOR7. GOVERNOR MOTOR8. MAP VACUUM PORT9. PCV VACUUM PORT10. GOVERNOR THROTTLE BODY

    Figure 8. Fuel System Components

    8

  • 2200 SRM 766 Description and Operation

    The fuel control system is controlled by the ECM. Thepurpose of the fuel control system is to deliver fuel tothe engine for the most efficient operation in all con-ditions called modes. The Starting Mode and theRun Mode are described in the paragraphs underHow ECM Begins Operation. When the ECM is inthe Run Mode, the ratio of the air and fuel mixtureis controlled for best operating conditions.

    The Acceleration Mode occurs when the ECMsenses rapid changes in the throttle position andmanifold pressure. The ECM sends additional fuelto the engine.

    The Deceleration Mode occurs when the ECMsenses rapid changes in the throttle position andmanifold pressure. The ECM reduces fuel to theengine. If the deceleration is very fast, the ECM canstop the fuel supply completely for short periods.

    Voltage Correction Mode. When battery voltageis low, the ECM can make adjustments for a weakspark from the distributor. The ON time for the fuelinjectors can be increased, the engine idle can be in-creased, and the ignition dwell time can be increased.

    Fuel Shut-Off Mode. When the ignition switch isturned to OFF, the ECM stops the pulses to the fuelinjectors. This procedure prevents a condition calleddieseling in a gasoline engine. Also, no fuel is sent tothe engine if there are no reference pulses from thedistributor. This condition indicates that the engineis not running.

    If the ECM senses that the engine speed is above themaximum set in the EEPROM, the fuel to the engineis stopped. This action normally occurs if the gover-nor is not operating correctly.

    INJECTION THROTTLE BODYThis system is similar to a carburetor system becauseit has a throttle body installed on an inlet manifold.There are two injectors in the throttle body that con-trol the air and fuel mixture. See Figure 9.

    The fuel injection system is controlled by the ECM.The basic function of the fuel injection system is to

    control the fuel delivery for the most efficient opera-tion of the engine. Fuel is sent to the throttle bodyinjection unit by the fuel pump. The ECM senses theoperation of the engine from the signals from its sen-sors, and controls the air and fuel ratio to the engineby controlling the operation of the fuel injectors andthe spark timing. The ECM controls the air and fuelratio for the best operating conditions of the engine.All modes of engine operation are controlled by theECM and the conditions set in its EEPROM.

    The following paragraphs describe the InjectionThrottle Body (ITB) fuel injection system designedby Dana/Epic. See Figure 9. The Injection ThrottleBody has the following assemblies: Fuel injectors Fuel pressure regulator Fuel pressure check valve

    Fuel InjectorsThe fuel injectors are solenoids controlled by theECM. The ECM energizes a solenoid which lifts anormally closed ball valve from its seat. The fuel isunder a constant pressure and is injected in a conespray pattern into the bore of the throttle body abovethe throttle plate. The fuel which is not used by thefuel injector flows through the pressure regulatorand returns to the fuel tank.

    Fuel Pressure RegulatorThe fuel pressure regulator is part of the fuel me-tering assembly of the ITB. The function of the fuelpressure regulator is to keep a constant fuel pres-sure at the fuel injectors during all operating modes.An air chamber and a fuel chamber are separated bya diaphragm-operated relief valve and a calibratedspring. Fuel pressure at the fuel injectors is con-trolled by the difference in pressure on each side ofthe diaphragm. The fuel pressure from the fuel pumpon one side of the diaphragm acts against the forcefrom the calibrated spring on the other side of the di-aphragm.

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  • Description and Operation 2200 SRM 766

    1. FUEL INJECTOR (2)2. INJECTION THROTTLE BODY3. FUEL FITTINGS (2)

    4. FUEL PRESSURE REGULATOR5. FUEL PRESSURE CHECK VALVE6. CONNECTOR TO ECM

    Figure 9. Injection Throttle Body Assembly

    GOVERNOR THROTTLE BODY ASSEMBLYThe following components are included in the Gover-nor Throttle Body assembly (see Figure 10): Governor throttle body Governor motor Throttle position sensor (TPS) Idle air control valve Vacuum ports (see Figure 8)

    The governor prevents engine speeds above the speci-fication when operating with light loads, and permitsthe throttle to open for full power for heavy loads.

    When the engine speed increases to its maximumrpm, the governor motor controls the actual positionof the throttle plates from signals from the ECM. The

    ECM senses the engine speed and load, and controlsthe engine speed within the specifications.

    A network of engine sensors (throttle position sen-sor, coolant temperature sensor, manifold absolutepressure sensor, and distributor reference pulses)send data about operating conditions to the ECM.The ECM uses the data to determine whether or notgoverned operation is needed.

    When the engine speed is less than approximately2150 rpm, the governor motor is not energized and areturn spring keeps the governor motor lever at itsparked position. The throttle plates can move withthe position of the throttle lever cam and no governoraction is used.

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  • 2200 SRM 766 Description and Operation

    1. IDLE AIR CONTROL (IAC) VALVE2. ADAPTER3. GASKET4. GOVERNOR THROTTLE BODY5. GOVERNOR DRIVE MOTOR

    6. SPACER7. THROTTLE POSITION SENSOR8. RETAINER9. CAPSCREW (2)

    Figure 10. Governor Throttle Body Assembly

    Throttle Position Sensor (TPS)The throttle position sensor is fastened to the end ofthe governor drive motor. The function of the throttleposition sensor is to sense the throttle position andsend a signal to the ECM. This information permitsthe ECM to generate the correct pulses to the fuelinjectors for fuel control. If the throttle position sen-sor indicates a fully opened throttle to the ECM, theECM then increases the pulse width to the fuel in-jectors. An increased pulse width increases the fuelflow.

    When the throttle shaft rotates to open the throt-tle plates, this rotation turns a potentiometer in thethrottle position sensor. This rotation of the poten-tiometer causes a variation in the voltage signal tothe ECM. The reference voltage is approximately 4.5volts at full open throttle and 0.5 volts at engine idle.

    Idle Air ControlThe idle speed of the engine is controlled by the ECMthrough the idle air control valve. The idle air con-trol valve has a linear DC step motor that moves a

    pintle valve to control the idle air system. See Fig-ure 11. The shaft of the pintle valve moves through256 steps. The step motor moves the pintle one stepfor each count that it receives from the ECM. Eachvoltage pulse from the ECM to move the pintle valveis a count.

    1. LINEAR DC STEPMOTOR

    2. PINTLE VALVE3. O-RING

    Figure 11. Idle Air Control Valve

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  • Description and Operation 2200 SRM 766

    This movement of the pintle valve controls the air-flow around the throttle plates. This airflow con-trols the engine idle speed at all operating temper-atures. A minimum idle is set at the factory with asetscrew. This minimum setting is for engine idle atsea level and normal operating conditions. A heavierload from the alternator, hydraulic pumps, and otheraccessories will cause the ECM to set a higher num-ber of counts on the pintle valve.

    The number of counts that indicates position of thepintle valve can be seen when a scan tool is connectedfor troubleshooting.

    When the engine speed increases toward approxi-mately 2500 rpm, the ECM sends signals to the gov-ernor control module to energize the governor motor.The governor control lever moves from its parked po-sition to control the opening of the throttle plates.If the engine load increases and the engine rpm de-creases, the governor motor opens the throttle platesfurther. If the governor system is not operating cor-rectly, the ECM will stop fuel to the engine at enginespeeds greater than 2900 rpm.

    Vacuum PortsThe governor throttle body has two vacuum ports onthe side of the assembly body. See Figure 8. Thesevacuum ports provide a source of vacuum for theMAP sensor and PCV valve that need a vacuumsource to operate.

    Fuel PumpThe fuel injection system must have a constant fuelpressure to operate correctly (see Figure 12). A checkfor the correct fuel pressure is often the first testwhen troubleshooting a fuel injection system. A testport is installed in the injector throttle body for thispurpose.

    A small turbine pump connected to an electric motoris installed in the fuel tank below the liquid level. SeeFigure 12. The fuel pressure regulator on the throttlebody keeps the fuel pressure at a constant 69 kPa(10 psi). Fuel that is not used by the throttle body isreturned to the fuel tank. Baffles are installed in thefuel tank to make sure that fuel is always availableto the fuel pump during normal operation of the lifttruck.

    1. FUEL SENDERCONNECTOR

    2. FUEL PUMPCONNECTOR

    3. FUEL INLET WITHSHUTOFF VALVE

    4. FUEL OUTLETWITH SHUTOFFVALVE

    5. FUEL PUMP

    Figure 12. Fuel Pump

    A fuel filter must be used in series with the fuel pumpto prevent any dirt from entering the fuel injectors inthe throttle body. The orifices in the fuel injectors arevery small in diameter and a particle of dirt can stopthe operation. A liquid level sender for the fuel gaugeis often fastened to the support for the fuel pump.

    A fuse and relay switch for the fuel pump is on amount in the engine compartment. See Figure 2.When the key switch is first turned to ON, the ECMenergizes the fuel pump relay for 2 seconds. This ac-tion quickly raises the fuel pressure to the fuel injec-tors. If the engine is not started within 2 seconds, theECM de-energizes the fuel pump relay and the fuel

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  • 2200 SRM 766 Description and Operation

    pump goes to OFF. When the engine is cranked bythe starter, the ECM energizes the fuel pump relayagain so that the fuel pump operates.

    This ECM control also prevents the fuel pump fromoperating if the ignition switch is turned to ON andthe engine is not running. This control prevents emp-tying the fuel tank through an open fuel line if theengine is not running and the ignition switch staysON.

    When the engine is running or being cranked by thestarter, the ECM receives reference pulses from theEST distributor or the DIS module. The ECM thenenergizes the fuel injectors.

    ECM SENSORS AND CONTROLLERS

    Manifold Absolute Pressure (MAP)The Manifold Absolute Pressure (MAP) sensor is apressure transducer that measures changes in thepressure in the intake manifold. See Figure 13.The pressure changes are a result of engine loadand speed changes. The MAP sensor converts thesepressure changes to a signal voltage to the ECM.

    1. SENSOR 2. ELECTRICALCONNECTOR

    Figure 13. Manifold Absolute Pressure (MAP)Sensor

    The ECM sends a 5-volt reference signal to the MAPsensor. When the pressure in the intake manifoldchanges, the electrical resistance in the MAP sensoralso changes. The change in the voltage signal fromthe MAP sensor enables the ECM to sense the pres-sure in the intake manifold.

    A closed throttle causes a low pressure (high enginevacuum) in the intake manifold. This low pressurecauses a low voltage signal from the MAP sensor tothe ECM. A fully opened throttle causes a higherpressure (low engine vacuum) in the intake manifold.This higher pressure causes a higher voltage signalfrom the MAP sensor to the ECM. These pressurechanges indicate the load on the engine and senda signal to the ECM. The ECM then calculates thespark timing and fuel requirements for best engineperformance.

    The MAP sensor also measures the barometric pres-sure when the key switch is turned to ON and beforethe engine is started. The ECM stores the baromet-ric pressure (BARO signal) after the engine is run-ning. This method enables the ECM to automaticallyadjust the ignition timing for different altitudes andatmospheric conditions.

    Coolant Temperature Sensor (CTS)The Coolant Temperature Sensor (CTS) is a resistorthat changes its resistance value when the temper-ature changes (thermistor). This sensor is installedin the engine coolant system. A low coolant temper-ature makes the thermistor have a high resistance[100,700 ohms at 40 C ( 40 F)]. A higher coolanttemperature makes the thermistor have a lower re-sistance [77 ohms at 130 C (266 F)].NOTE: If the connection between the CTS and theECM is open during starting or operation of the en-gine, the ECM determines that the engine is cold andadjusts the air and fuel mixture to the full 1.5:1 ra-tio. This condition can flood the engine with fuel.

    The Coolant Temperature Sensor (CTS) uses a ther-mistor to control the signal voltage to the ECM. TheECM applies a 5-volt reference voltage to the CTS.The measured voltage will be high when the enginecoolant is cold. The measured voltage will be lowerwhen the engine coolant is at operating temperature.The ECM will adjust the range of the air and fuel ra-tio between 1.5:1 at 36 C ( 33 F) to 14.7:1 at 94 C(201 F) from the CTS signal. The ECM will also ad-just the ignition timing for more spark advance whenthe engine coolant is cold and less spark advancewhen the engine coolant is hot. An engine at operat-ing temperature normally needs less spark advance.

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  • NOTES

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  • TECHNICAL PUBLICATIONS

    2200 SRM 766 8/02 (8/99) Printed in U.S.A.

    tocElectronic Engine ControlSafety Precautions Maintenance and RepairGeneralDescription and OperationGeneralECM (Electronic Control Module)Diagnostic ConnectorHow ECM Begins Operation

    Electronic Engine ControlWhat ECM DoesPulse Generator, EST DistributorEST ModuleWhen Engine is Being StartedWhen Engine is RunningElectronic Control Module (ECM) With EST Distributor, Correction

    Fuel ControlInjection Throttle BodyFuel InjectorsFuel Pressure Regulator

    Governor Throttle Body AssemblyThrottle Position Sensor (TPS)Idle Air ControlVacuum PortsFuel Pump

    ECM Sensors and ControllersManifold Absolute Pressure (MAP)Coolant Temperature Sensor (CTS)