Fuel Injection System - Tbi GMC Cab & Chassis R2500

COMPONENT TESTING

Note. Specific component testing information not available. Refer to any tests performed during REMOVAL & INSTALLATION or OVERHAUL procedures

APPLICATION

ROCHESTER THROTTLE BODY NO.

IDENTIFICATION

The throttle body injection identification number is stamped on mounting flange, on throttle lever side. (Scheme 19) Alphabetical code letters are stamped on the throttle body at external tube locations to identify vacuum hose connections.

All Astro, Safari and "S" series vehicles use either the model 220 or model 700 TBI unit. The "R" and "V" series use the model 220 TBI unit. All "G" series vans and "P" series trucks use the model 220 TBI unit.

Scheme 19

DESCRIPTION

The throttle body fuel injection system consists of 7 major sub-assemblies: fuel supply system, throttle body assembly, Idle Air Control (IAC) System, Electronic Control Module (ECM), Electronic Spark Timing (EST), data sensors, and emission controls. Fuel is supplied to the engine through electronically pulsed injector(s) located in the throttle body assembly on top of intake manifold. The ECM controls the amount of fuel metered through the injector(s) based upon engine demand.

FUEL SUPPLY SYSTEM

An electric fuel pump (located inside fuel tank as an integral part of the fuel gauge sending unit) supplies fuel under pressure to the throttle body assembly. On most engines, a fuel pump relay controls fuel pump operation. When the ignition is on, the fuel pump relay activates the fuel pump for 2 seconds to prime the injector(s). On some 5.7L and 7.4L engines, a fuel module circuit is installed so that the fuel pump will run for 20 seconds when ignition is turned on.

On all engines, if the ECM does not receive reference pulses (engine cranking) from the distributor after this priming period, the ECM deactivates the fuel pump relay. The fuel pump relay will be activated again when the ECM receives distributor reference pulses.

As a back-up system to the fuel pump relay, the fuel pump can also be activated by oil pressure sending unit. The sending unit has 2 internal circuits. One circuit operates the oil pressure indicator in the instrument panel.

The second circuit is normally an open switch which closes when the oil pressure reaches about 4 psi (.3 kg/cm 2 ). If fuel pump relay fails, oil pressure sending unit will close, and supply voltage to fuel pump.

THROTTLE BODY ASSEMBLY

The model 220 throttle body assembly consists of a fuel meter cover with a built in fuel pressure regulator, a fuel meter body with 2 fuel injectors, a throttle body with 2 throttle valves, an Idle Air Control (IAC) valve, and a Throttle Position Sensor (TPS).

The model 700 throttle body assembly consists of a fuel meter body with one fuel injector, a fuel pressure regulator, a throttle body with one throttle valve, an IAC valve, and a TPS sensor.

The throttle body portion may contain ports located above or below the throttle valve to generate vacuum signals for EGR valve, MAP sensor, and fuel vapor canister purge system.

FUEL PRESSURE REGULATOR

The pressure regulator is a diaphragm-operated relief valve with injector pressure acting on one side and air cleaner pressure acting on the other. The pressure regulator maintains a constant pressure drop of about 10 psi (.7 kg/cm 2 ) across injector(s), throughout all engine operating conditions. The model 700 fuel pressure regulator may be disassembled and repaired.

FUEL INJECTOR

The fuel injector is a solenoid-operated device controlled by the ECM. The ECM activates the solenoid which lifts a normally closed ball valve off its seat. Fuel under pressure is injected in a conical spray pattern at the walls of throttle body bore, above the throttle valve. Excess fuel passes through the pressure regulator and is returned to the fuel tank.

IDLE AIR CONTROL (IAC) SYSTEM

The IAC system consists of an electrically controlled motor (actuator) which positions the IAC valve in the air by-pass channel around the throttle valve. The ECM calculates the desired position of the IAC valve based upon battery voltage, coolant temperature, engine load, and engine RPM to control idle speed while preventing stalls due to engine load changes.

If engine RPM is lower than desired, the ECM activates the IAC motor to retract the IAC valve. When the IAC valve is retracted, more air is diverted around the throttle valve to increase engine speed. If engine speed is higher than desired, the ECM activates the IAC motor to extend the IAC valve. When the IAC valve is extended, less air is diverted around the throttle valve, decreasing engine speed.

ELECTRONIC CONTROL MODULE

The Electronic Control Module (ECM) receives and processes information from all data sensors to produce the proper pulse duration ("on" time) for the injector(s), correct idle speed and proper spark timing. The ECM performs calculations to control the following operating conditions: engine start, engine running, fuel enrichment during acceleration, lean fuel mixture during deceleration, fuel cut-off and battery voltage correction.

During engine starts, the ECM delivers an injector pulse for each distributor reference pulse received (synchronized mode). The injector pulse width is based upon coolant temperature and throttle position. The air/fuel ratio is determined by the ECM when the throttle position is less than 80 percent open. Engine starting air/fuel ratio ranges from 1.5:1 at -33°F (-36°C) to 14.7:1 at 201°F (94°C).

If the engine is flooded, the driver must depress the accelerator pedal all the way down. At this position, the ECM calculates injector pulse width equal to an air/fuel ratio of 20:1. This air/fuel ratio will be maintained as long as the throttle valve remains wide open and engine speed is below 600 RPM. If the throttle position becomes less than 80 percent open and/or engine speed exceeds 600 RPM, the ECM changes the injector pulse width to that used during engine starting.

When the engine is running above 400 RPM, the ECM operates in the open loop mode. In open loop, the ECM calculates injector pulse width based upon coolant temperature and manifold absolute pressure. The engine will remain in open loop operation until the oxygen sensor reaches operating temperature, the coolant temperature reaches a preset temperature, and a specific period of time has elapsed after the engine starts. When all these conditions are met, the ECM operates in the closed loop mode. In closed loop, the ECM controls injector pulse width based upon oxygen sensor signals to maintain the air/fuel mixture ratio close to 14.7:1.

During deceleration, the ECM looks at changes in throttle position and manifold pressure and reduces fuel to fuel injector(s). When deceleration is sudden, the ECM can cut fuel off completely for short periods of time. When battery voltage is low, the ECM can compensate for a weak ignition system by increasing injector "on" time, increasing idle RPM, and increasing ignition dwell.

The ECM used on fuel injected vehicles has a "learning" capacity which allows it to make minor corrections to fuel system. If the battery is disconnected, the "learning" process must begin all over again. During this period, a change may be noted in vehicle performance. To "teach" the vehicle, ensure the vehicle is at normal operating temperature. The vehicle should then be driven at part throttle, moderate acceleration and idle until performance returns.

DATA SENSORS

Each sensor furnishes an electrical signal to the ECM, modifying injector pulse width to conform to engine operating conditions. (Scheme 20), (Scheme 21) and (Scheme 22). These sensors are as follows

Coolant Temperature Sensor (CTS)

The coolant temperature sensor is located in thermostat housing. It is a variable resistor (thermistor) type sensor, and transmits an electrical signal to the ECM proportionate to engine temperature. A low coolant temperature produces a high resistance while a high coolant temperature produces a low resistance.

The ECM supplies a 5-volt signal to the coolant temperature sensor and measures the voltage that returns. By measuring the voltage drop between the 2 readings, the ECM is informed of engine coolant temperature. Coolant temperature is used for fuel management, idle air control, spark timing, EGR operation, canister purge operation and other engine operating functions.

Oxygen Sensor

The oxygen sensor monitors the oxygen content of the exhaust gases. As the oxygen content of the exhaust gases increases relative to the surrounding atmosphere, a lean fuel mixture is indicated by a low voltage output. As the oxygen content decreases, a rich fuel mixture is indicated by a higher voltage output. The ECM interprets the electrical signal and adjusts the injector pulse width to maintain the air/fuel ratio close to 14.7 to 1.

Manifold Absolute Pressure (MAP) Sensor

The MAP sensor is a variable resistor which measures the changes in the intake manifold pressure which result from engine load and speed changes. The pressure measured by the MAP sensor is the difference between barometric pressure (atmospheric air) and manifold pressure (vacuum).

A closed throttle condition (engine coast down) would produce a low MAP reading while a wide open throttle condition (engine acceleration) would produce a high MAP reading. The high value is produced because the pressure inside the intake manifold (vacuum) is the same as the pressure outside the manifold (atmospheric air).

The ECM supplies a 5-volt reference signal to the MAP sensor. As MAP changes, the electrical resistance of the sensor also changes. By monitoring sensor output voltage, the ECM is informed of intake manifold pressure. A higher pressure (high voltage) requires more fuel, while a lower pressure (low voltage) requires less fuel.

Vehicle Speed Sensor (VSS)

This sensor is mounted behind the speedometer in instrument cluster. It provides the ECM with pulses to determine vehicle speed. This information is used by the ECM to control Torque Converter Clutch (TCC), shift indicator light, and cruise control system.

Throttle Position Sensor (TPS)

The TPS is mounted on side of the throttle body and is connected to the throttle shaft. As throttle valve angle changes, the resistance of the sensor also changes. The ECM supplies a 5-volt reference signal to the TPS. A closed throttle condition produces high resistance at the sensor and the output signal to the ECM will be low (about .5 volts). A wide open throttle condition produces low resistance at the sensor. The output signal to the ECM will be high (about 5 volts).

By monitoring the output voltage of the TPS and comparing that value to the reference signal, the ECM can calculate fuel requirements based upon throttle valve angle (driver demand).

Note. For information on other sensors that are used by the ECM to control engine performance and other systems, refer to GENERAL MOTORS COMPUTER COMMAND CONTROL article in COMPUTERIZED ENGINE CONTROLS section.

Scheme 20

Scheme 21

Scheme 22

PRELIMINARY CHECKS

Check or perform the following items before beginning diagnosis of fuel injection system

1. Check vacuum hoses for cracks, kinks, and proper routing.
2. Check for air leaks at throttle body flange and at intake manifold.
3. Check ignition system.
4. Check all electrical connections and terminals (including battery).
5. Perform DIAGNOSTIC CIRCUIT CHECK. See GENERAL MOTORS COMPUTER COMMAND CONTROL article in COMPUTERIZED ENGINE CONTROL section.
6. If engine cranks but will not run, see CHART A-3 in GENERAL MOTORS COMPUTER COMMAND CONTROL article in COMPUTERIZED ENGINE CONTROL section.

CUTS OUT OR MISSES

1. Check for a cylinder that misses by disconnecting IAC motor. Start engine. Using insulated pliers, remove spark plug wires one at a time. If there is an RPM drop on all cylinders, see «ROUGH, UNSTABLE, INCORRECT IDLE OR STALLING»(/gmc/cab-chassis-r2500/1987-1987/remont/testing-diagnostics/#fuel-injection-system-tbi__rough-unstable-incorrect-idle-or-stalling) . Reconnect IAC motor.
2. If there is no RPM drop on one or more cylinders, check spark at suspected cylinder(s). If there is no spark, check ignition system. If there is spark, remove and inspect spark plugs.
3. Check fuel filter for restrictions. Check fuel for water contamination. Check fuel pressure. See «FUEL SYSTEM PRESSURE TEST»(/gmc/cab-chassis-r2500/1987-1987/remont/testing-diagnostics/#fuel-injection-system-tbi__fuel-system-pressure-test) . If okay, check engine for mechanical defects (worn rocker arms, broken valve springs, etc.).

DIESELING, RUN-ON

Check fuel injector(s) for leaks by applying 12 volts to fuel pump test terminal (to turn on fuel pump and pressurize system). Visually check injector(s) and throttle body injector assembly for fuel leaks.

HARD STARTING (HOT OR COLD)

1. Check fuel for water contamination. Check fuel pressure. See «FUEL SYSTEM PRESSURE TEST»(/gmc/cab-chassis-r2500/1987-1987/remont/testing-diagnostics/#fuel-injection-system-tbi__fuel-system-pressure-test) . Check TPS for sticking or binding. Check EGR valve operation. See appropriate EGR SYSTEM CHECK chart in GENERAL MOTORS COMPUTER COMMAND CONTROL article in COMPUTERIZED ENGINE CONTROLS section.
2. On Astro, Safari and "S" series trucks, check fuel pump relay by connecting test light between pump test terminal and ground. Test light should be on for 2 seconds after turning ignition on. NOTE: On 7.4L engine and some 5.7L engines, a fuel module circuit will activate fuel pump for 20 seconds after turning ignition A hard start condition may be caused if this circuit is not functioning.
3. Check for faulty fuel pump check valve. To check for this condition, turn ignition off. Disconnect fuel line at fuel filter. Remove fuel tank filler cap. Connect radiator test pump to fuel line and apply 15 psi (1.1 kg/cm 2 ). If pressure is held for 60 seconds, check valve is okay.
4. Check ignition system. If engine starts but then immediately stalls, open distributor by-pass line. If engine then starts and runs okay, replace distributor pick-up coil.
5. If engine hard start occurs with engine at normal operating temperature, check crank signal. See CRANK SIGNAL DIAGNOSIS chart in GENERAL MOTORS COMPUTER COMMAND CONTROL article in COMPUTERIZED ENGINE CONTROLS section.
6. On vehicles between 8500-10,000 GVW ratings (5.7L and 7.4L engines), check fuel pump cycle system.

HESITATION, SAG OR STUMBLE

1. Perform all preliminary checks. Check fuel pressure. See «FUEL SYSTEM PRESSURE TEST»(/gmc/cab-chassis-r2500/1987-1987/remont/testing-diagnostics/#fuel-injection-system-tbi__fuel-system-pressure-test) . Check fuel for water contamination. Check TPS for binding or sticking. Check ignition timing.
2. Check alternator output voltage. Repair alternator if output voltage is less than 9 or more than 16 volts. Check for an open in HEI ground circuit and repair as required. Check canister purge system for proper operation.
3. Check EGR valve operation. See appropriate EGR SYSTEM CHECK chart in GENERAL MOTORS COMPUTER COMMAND CONTROL article in COMPUTERIZED ENGINE CONTROLS section.

POOR FUEL ECONOMY

1. Check engine thermostat heat range. Check fuel pressure. See «FUEL SYSTEM PRESSURE TEST»(/gmc/cab-chassis-r2500/1987-1987/remont/testing-diagnostics/#fuel-injection-system-tbi__fuel-system-pressure-test) . Check ignition timing.
2. Check Torque Converter Clutch (TCC) operation. See appropriate TORQUE CONVERTER CLUTCH ELECTRICAL DIAGNOSIS chart in GENERAL MOTORS COMPUTER COMMAND CONTROL article in COMPUTERIZED ENGINE CONTROLS section.

ROUGH, UNSTABLE, INCORRECT IDLE OR STALLING

1. Check ignition timing. Check Park/Neutral switch circuit. See PARK/NEUTRAL SWITCH DIAGNOSIS chart in GENERAL MOTORS COMPUTER COMMAND CONTROL article in COMPUTERIZED ENGINE CONTROLS section.
2. Check injector for leaks. See DIESELING, RUN-ON. Check fuel pressure. See FUEL SYSTEM PRESSURE TEST. If idle is rough only when engine is hot, perform the following checks: Check for vacuum leaks by installing Plug (J-330247) in idle air passage. If closed throttle engine speed is above 650 RPM, locate and correct vacuum leak. Check Park/Neutral switch circuit. See PARK/NEUTRAL SWITCH DIAGNOSIS chart in GENERAL MOTORS COMPUTER COMMAND CONTROL article in COMPUTERIZED ENGINE CONTROLS section. Check for sticking throttle shaft or binding linkage that may cause a high TPS voltage (open throttle indication). If binding occurs, the ECM will not control idle. Check TPS voltage. Reading should be less than 1.2 volts with throttle closed. Check EGR valve operation. See appropriate EGR SYSTEM CHECK chart in GENERAL MOTORS COMPUTER COMMAND CONTROL article in COMPUTERIZED ENGINE CONTROLS section. Check battery terminals, cables, and grounds straps for loose or corroded connections. Erratic voltage will cause IAC motor to change its position, resulting in poor idle quality. IAC valve will not move if voltage is below 9 or greater than 17.8 volts. On 2.5L engine, check power steering pressure switch. See POWER STEERING PRESSURE SWITCH chart in GENERAL MOTORS COMPUTER COMMAND CONTROL article in COMPUTERIZED ENGINE CONTROLS section. ECM should compensate for power steering loads. Check MAP sensor operation. Start and allow engine to idle. Disconnect MAP sensor electrical connector. If idle improves, substitute a known good sensor and retest. Check A/C for high refrigerant pressure. Check A/C compressor or relay. If inoperative, see appropriate A/C CLUTCH CONTROL DIAGNOSIS chart in GENERAL MOTORS COMPUTER COMMAND CONTROL article in COMPUTERIZED ENGINE CONTROLS section. Inspect oxygen sensor for silicon contamination from fuel or improper use of RTV sealant. Sensor may have a White, powdery coating, and will result in a high but false signal voltage (rich exhaust indication). Check PCV valve for proper operation by placing finger over inlet hole in valve end several times. Valve should snap back. If not, replace PCV valve. Perform compression test.

SURGING

1. Check EGR valve operation. See appropriate EGR SYSTEM CHECK chart in GENERAL MOTORS COMPUTER COMMAND CONTROL article in COMPUTERIZED ENGINE CONTROLS section.
2. Check ignition timing. Check fuel filter for restrictions. Check fuel pressure. See «FUEL SYSTEM PRESSURE TEST»(/gmc/cab-chassis-r2500/1987-1987/remont/testing-diagnostics/#fuel-injection-system-tbi__fuel-system-pressure-test) . Check alternator output voltage. Repair alternator if output voltage is less than 9 volts or more than 16 volts.
3. Check Torque Converter Clutch (TCC) operation. See appropriate TORQUE CONVERTER CLUTCH ELECTRICAL DIAGNOSIS chart in GENERAL MOTORS COMPUTER COMMAND CONTROL article in COMPUTERIZED ENGINE CONTROLS section.
4. Remove and inspect oxygen sensor for silicon contamination from fuel, or improper use of RTV sealant. Sensor may have a White, powdery coating and will result in a high, but false signal voltage (rich exhaust indication). Check ignition system.

FUEL SYSTEM PRESSURE RELIEF

1. On 2.5L engine, remove "FUEL PUMP" fuse from fuse block. Crank engine. Engine will start and run until fuel supply remaining in fuel lines is used. Engage starter for about 3 seconds to remove any remaining fuel. With ignition off, replace fuse.
2. On all other engines, fuel pressure is relieved and drops to zero when ignition is turned off. To minimize the risk of fire and personal injury, cover area to be disconnected with a shop rag. After use, place rag in approved container.

FUEL SYSTEM PRESSURE TEST

1. Turn engine off and relieve fuel pressure. See «FUEL SYSTEM PRESSURE RELIEF»(/gmc/cab-chassis-r2500/1987-1987/remont/testing-diagnostics/#fuel-injection-system-tbi__fuel-system-pressure-relief) . Remove air cleaner and plug air cleaner (THERMAC) vacuum port (model 700 TBI unit only).
2. Disconnect fuel line between throttle body and fuel filter. Install Fuel Pressure Gauge (J-29658A) between throttle body and in-line fuel filter. Start engine and observe fuel pressure reading.
3. Fuel pressure should be 9-13 psi (.6-.9 kg/cm 2 ). If not, see CHART A-6 FUEL SYSTEM PRESSURE TEST in GENERAL MOTORS COMPUTER COMMAND CONTROL article in COMPUTERIZED ENGINE CONTROLS section.
4. After testing, relieve fuel pressure. Remove fuel pressure gauge and connect fuel line to fuel filter. Start vehicle and check for leaks. Remove plug from throttle body vacuum port (model 700 TBI unit). Install air cleaner.

Locate coolant temperature sensor. Disconnect battery negative cable. Drain coolant below level of sensor. Disconnect electrical lead and remove sensor. Handle CTS with care to prevent damage to sensor calibration. To install, reverse removal procedure.

ELECTRONIC CONTROL MODULE (ECM)

Locate electronic control module. Disconnect battery negative cable. Disconnect electrical connectors from ECM. Remove ECM mounting hardware and ECM. To install, reverse removal procedure.

FUEL PUMP

1. Relieve fuel system pressure. See «FUEL SYSTEM PRESSURE RELIEF»(/gmc/cab-chassis-r2500/1987-1987/remont/testing-diagnostics/#fuel-injection-system-tbi__fuel-system-pressure-relief) . Disconnect battery negative cable. Raise vehicle on hoist and lower fuel tank. Turn lock ring counterclockwise and remove fuel lever sending unit and pump assembly.
2. Remove fuel pump from fuel lever sending unit by pulling fuel pump up into attaching hose while pulling outward away from bottom support. Make sure not to damage rubber insulator and strainer. To install, reverse removal procedure.

FUEL PUMP RELAY

Locate fuel pump relay. Remove electrical connector, mounting screws, and relay. To install, reverse removal procedure.

Remove instrument cluster and speedometer assembly. Disconnect VSS from speedometer. Disconnect electrical connector and remove VSS. To install, reverse removal procedure.

1. Locate MAP sensor on air cleaner or bracket next to throttle body. Disconnect vacuum tube and wiring from MAP sensor. On bracket mounted MAP sensors, remove screws and sensor.
2. On air cleaner mounted MAP sensors, remove air cleaner cover and MAP sensor bracket retaining clip. Remove MAP sensor from bracket. To install, reverse removal procedure.

1. Locate oxygen sensor. Disconnect battery negative cable. Disconnect sensor at electrical connector. DO NOT remove wire (pigtail) from oxygen sensor.
2. Carefully back sensor out of exhaust manifold. Handle sensor with care and do not allow dirt or other foreign matter to contact louvered end of sensor.
3. To install, reverse removal procedure. Coat threads of replacement sensor with Anti-Seize Compound (Part No. 3613695). Tighten sensor to 30 ft. lbs. (41 N.m).

POWER STEERING PRESSURE SWITCH

Locate power steering pressure switch on inlet pipe of power steering gear. Disconnect connector and remove switch. To install, reverse removal procedure.

Removal

1. Disconnect air cleaner (THERMAC) hose from engine fitting (model 700 TBI unit only). Remove air cleaner, adapter, and gasket. Disconnect electrical leads and IAC valve, throttle position sensor, and fuel injector(s). NOTE: On model 220 TBI units, squeeze plastic tabs on injectors and pull straight up.
2. Disconnect grommet with wires from throttle body. Disconnect throttle linkage, return spring and cruise control linkage (if equipped). Label and disconnect all vacuum hoses from throttle body.
3. Relieve fuel pressure. See «FUEL SYSTEM PRESSURE RELIEF»(/gmc/cab-chassis-r2500/1987-1987/remont/testing-diagnostics/#fuel-injection-system-tbi__fuel-system-pressure-relief) . Disconnect fuel lines from throttle body. Remove throttle body mount bolts/nut. Remove throttle body.

Installation

To install, reverse removal procedure. Ensure throttle body and intake manifold sealing surfaces are clean. Always use new throttle body gasket. Check fuel system for leaks by turning ignition on, but without starting engine.

Remove air cleaner assembly. Disconnect electrical lead from TPS sensor. Remove attaching screws, lock washers, retainers, and TPS sensor. To install, reverse removal procedure. Make sure TPS lever lines up with throttle actuator lever. Use Loctite on TPS attaching screws.

ADJUSTMENTS

Note. See appropriate article in TUNE-UP section.

Fuel Meter Cover

1. Remove throttle body and place assembly on Holding Fixture (J-9789-118) to prevent damage to throttle valves. Disconnect electrical leads from fuel injectors. Remove cover attaching screws and lock washers. (Scheme 24)
2. Lift off fuel meter cover with fuel pressure regulator assembly attached. NO NOT remove fuel meter cover gasket at this time. Remove fuel pressure regulator dust seal from fuel meter body.

1. With fuel meter cover gasket in place, use a screwdriver to carefully pry injectors away from fuel meter body. Carefully lift injectors out with a twisting motion. (Scheme 23)
2. Remove small "O" ring from nozzle end of injector. Carefully rotate injector filter back and forth to remove from base of injector. Remove large "O" ring and back-up washer from top of injector cavity.

Scheme 23

Fuel Meter Body

Remove fuel inlet and outlet nuts and gaskets from fuel meter body. Remove fuel meter body attaching screws and lock washers. Remove fuel meter body and gasket.

Throttle Body

Remove throttle position sensor. Invert throttle body assembly and place on clean, flat surface. Remove screws and idle air control valve (7.4L engine) or remove idle air control valve by using a 1-1/4" (32 mm) wrench.

1. Remove throttle body and place assembly on Holding Fixture (J-9789-118) to prevent damage to throttle valves. Remove screw and injector retainer. (Scheme 24)
2. Place a screwdriver over fuel meter body. Use a second screwdriver to carefully pry injector away from fuel meter body. Remove upper and lower "O" rings from injector or fuel injector cavity.

1. Remove fuel pressure regulator attaching screws while keeping pressure regulator compressed. Remove pressure regulator cover, spring seat, spring, and diaphragm. (Scheme 24) WARNING: The pressure regulator includes a spring under heavy tension which may cause personal injury if released.
2. Inspect pressure regulator seat for pitting or other damage. If damaged, replace fuel meter body. To do so, remove fuel meter body screws and washers. Remove fuel meter body from throttle body. Remove and discard fuel meter body gasket.

Remove tube assembly and gasket. Remove throttle position sensor and Idle Air Control (IAC) valve.

CLEANING & INSPECTION

1. Clean all metal parts in a cold immersion-type cleaner and blow dry with compressed air.
2. DO NOT immerse throttle position sensor, idle air control valve, fuel injector(s), fuel filter, or fuel meter cover and pressure regulator assembly in cleaner.
3. Inspect throttle body assembly casting surfaces for damage.

1. Before installing idle air control valve, measure distance between tip of valve pintle and mounting surface. Distance should not exceed 1-1/8" (28 mm). (Scheme 24)
2. On 7.4L engine Idle Air Control (IAC) valve and IAC valves with collar on electrical connector, exert firm pressure on pintle while moving pintle from side to side until distance is correct.
3. On idle air control valve without collar on connector, compress pintle retaining spring while turning pintle inward with a clockwise motion. Return spring to original position with straight portion of spring end aligned with flat surface of valve. NOTE: On 7.4L engines, the Idle Air Control (IAC) valve pintle diameter is 12 mm rather than 10 mm. Ensure replacement IAC valve pintle taper is correct.
4. Invert throttle body assembly and place on clean, flat surface. Install IAC valve and gasket. On 7.4L engine, tighten IAC valve screws to 28 INCH lbs. (3 N.m). Tighten threaded IAC valve to 13 ft. lbs. (18 N.m).
5. Place throttle body on holding fixture. Install throttle position sensor. Make sure throttle position sensor lever lines up with throttle actuator lever. Use Loctite on throttle position sensor attaching screws.

Scheme 24

Install fuel meter body gasket and fuel meter body on throttle body. Apply thread locking compound (supplied in service kit) on attaching screws. Install lock washers and screws. Install fuel inlet and outlet nuts and gaskets.

1. Using a slight twisting motion, install fuel injector filter on nozzle end of injector until seated against base. Ensure that large end of filter faces injector. Filter should cover raised rib at base of injector.
2. Lubricate "O" rings with automatic transmission fluid. Push small "O" ring on nozzle end of injector until seated against injector fuel filter. Install back-up washer in top recess of fuel meter body cavity.
3. Install large "O" ring directly above back-up washer. Press "O" ring into cavity until it is flush with top of fuel meter body casting surface. NOTE: "O" rings and back-up washer must be installed before fuel injector. Otherwise injector fuel leaks may occur.
4. Align raised lug on injector base with notch in fuel meter body cavity. Push down on injector until it is fully seated. Injector is correctly installed when electrical connections are parallel to throttle shaft.

1. Install new fuel pressure regulator dust seal into recess of fuel meter body. Install new fuel outlet gasket. Install new fuel meter cover gasket on fuel meter body. Install fuel meter cover.
2. Ensure pressure regulator dust seal and gaskets are in place. Apply thread locking compound (supplied in service kit) to cover screws. Install lock washers and screws.

1. Install tube assembly using a new gasket. Install throttle position sensor. Before installing idle air control valve, measure distance between tip of valve pintle and mounting surface. Distance should not exceed 1 1/8" (28 mm).
2. If distance is incorrect, exert firm pressure on pintle while moving pintle from side to side until distance is correct. The flange mounted IAC valve on 2.5L engines has a dual taper, 10 mm diameter pintle. Ensure replacement valve has same shape and diameter of valve removed.

1. Install new fuel meter body gasket. Ensure gasket cut-outs match openings in throttle body. Install fuel meter body and tighten screws. Install new pressure regulator diaphragm. Ensure diaphragm is seated in fuel meter body groove.
2. Install spring, spring seat, and cover. (Scheme 24) Apply Loctite to pressure regulator cover screws. While maintaining pressure on regulator cover and spring, install cover screws.

1. Lubricate "O" rings with automatic transmission fluid. Make sure upper "O" ring is in groove and that lower "O" ring is flush against filter. (Scheme 24)
2. Press injector into fuel cavity. Ensure injector electrical connector is facing cut-out in fuel meter body for wire grommet. Apply Loctite to injector retainer screw. Install injector retainer and screw.

TORQUE SPECIFICATIONS

TORQUE SPECIFICATIONS

See also:
• ROUGH, UNSTABLE, INCORRECT IDLE OR STALLING
• FUEL SYSTEM PRESSURE TEST
• FUEL SYSTEM PRESSURE RELIEF