Fuel Injection System - Tbi GMC Cab & Chassis S15

COMPONENT TESTING

Note. Specific component testing information not available. Refer to any tests performed during TROUBLE SHOOTING or TESTING procedures.

APPLICATION

ROCHESTER THROTTLE BODY NO.

IDENTIFICATION

The throttle body injection identification number is stamped on mounting flange, on throttle lever side. (Scheme 50) Alphabetical code letters are stamped on the throttle body at external tube locations to identify vacuum hose connections.

Throttle Body Identification Location. Scheme 50

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. A fuel pump relay controls fuel pump operation. When the ignition switch is turned on, the fuel pump relay activates the fuel pump for 2 seconds to prime the injector(s).

If the ECM does not receive reference pulses (engine cranking) from the distributor after this 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 INJECTOR ASSEMBLY

The throttle body injector assembly consists of 2 castings: a throttle body and a fuel meter body. Throttle body casting incorporates an IAC valve to control air flow, and a throttle position sensor. Throttle body casting may contain ports to generate vacuum signals for EGR valve, MAP sensor and canister purge system.

The fuel meter body has a cover with built in pressure regulator, and fuel injector(s) to supply fuel to engine. 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 the injector, throughout all engine operating conditions. (Scheme 51)

Sectional View of Throttle Body Assembly. Scheme 51

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 speed to control idle speed while preventing stalls due to engine load changes.

If engine speed 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 220°F (104°C). The lower the coolant temperature, the longer the injector pulse width (richer air/fuel mixture ratio). The higher the coolant temperature, the shorter the injector pulse width (leaner air/fuel ratio).

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.

Fuel enrichment during acceleration is provided by the ECM. Sudden opening of the throttle valve causes a rapid increase in manifold absolute pressure. Pulse width is directly related to manifold pressure, throttle position and coolant temperature. The higher the manifold pressure and the wider the throttle angle, the wider the pulse width (richer mixture). During enrichment, the injector pulses are not in proportion to distributor reference signals. Any reduction in throttle angle cancels fuel enrichment.

During normal deceleration, the ECM calculates the injector pulse width in a manner similar to that used for fuel enrichment, and fuel output is reduced. This reduction in available fuel serves to remove residual fuel from intake manifold. During sudden deceleration, when manifold absolute pressure, throttle position and engine speed are reduced to preset levels, fuel flow is cut-off completely to remove fuel from the engine. This deceleration fuel cut-off overrides the normal deceleration mode. During either deceleration mode, injec-tor pulses are not in proportion to distributor reference signals.

Battery voltage corrections by the ECM are performed during all operating modes. As battery voltage decreases, the ECM increases the injector pulse width with a correction factor stored in the ECM's memory. The ECM can compensate by increasing injector "on" time, increasing idle RPM, and increasing ignition dwell.

The ECM used on fuel injected vehicles has a "learning" capacity. 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. 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. Low coolant temperature produces high resistance while high coolant temperature produces 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 used in the fuel injection system is a closed-end Zirconia sensor placed in the exhaust gas stream. The sensor is constructed in such a way that the exhaust gases pass by the bottom of the sensor and atmospheric air is admitted at the top of the sensor. The Zirconia produces an electrical voltage when exposed to oxygen, similar to a small battery. By comparing the amount of oxygen present in the exhaust gases to the amount of oxygen in the atmosphere, the sensor produces a signal which is proportional to the oxygen concentration in 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.

Note. No attempt should be made to measure oxygen sensor voltage output. Current drain of conventional voltmeter could permanently damage sensor, shift sensor calibration and/or render sensor unusable. DO NOT connect jumper wire, test leads or other electrical connectors to sensor.

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 the IAC motor.

Note. The vehicle should not be driven without the vehicle speed sensor installed.

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 (accelerator pedal moved), 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 CONTROL section.

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. 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 missing cylinder 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. Reconnect IAC motor.
2. If there is no RPM drop on one or more cylinders, check spark at suspected cylinder(s). If 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. 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. Check TPS for sticking or binding. Check EGR valve operation. See CHART C-7 (2.8L and 4.3L ) or CHART C-7A (2.5L) in GENERAL MOTORS COMPUTER COMMAND CONTROL article in COMPUTERIZED ENGINE CONTROL section.
2. Check fuel pump relay by connecting test lamp between pump test terminal and ground. Test lamp should be on for 2 seconds after turning ignition on. Check for faulty fuel pump check valve. To check for this condition, proceed as follows: turn ignition off.
3. 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 CHART C-1B in GENERAL MOTORS COMPUTER COMMAND CONTROL article in COMPUTERIZED ENGINE CONTROL section.

HESITATION, SAG OR STUMBLE

1. Perform all preliminary checks. Check fuel pressure. See FUEL SYSTEM PRESSURE TEST. Check fuel for water contamination. check TPS for binding or sticking. Check ignition timing.
2. Check alternator output voltage. Repair if less than 9 or more than 16 volts. Check for an open in HEI ground circuit. Repair as required. Check canister purge system for proper operation.
3. Check EGR valve operation. See CHART C-7 (2.8L and 4.3L ) or CHART C-7A (2.5L) in GENERAL MOTORS COMPUTER COMMAND CONTROL article in COMPUTERIZED ENGINE CONTROL section.

POOR FUEL ECONOMY

1. Check engine thermostat heat range. Check fuel pressure. See FUEL SYSTEM PRESSURE TEST. Check ignition timing.
2. On 2.8L and 4.3L engines, check Transmission Converter Clutch (TCC) operation. See CHART C-8 in GENERAL MOTORS COMPUTER COMMAND CONTROL article in COMPUTERIZED ENGINE CONTROL section.

ROUGH, UNSTABLE, INCORRECT IDLE OR STALLING

1. Check ignition timing. Check Park/Neutral switch circuit. See CHART C-1A in GENERAL MOTORS COMPUTER COMMAND CONTROL article in COMPUTERIZED ENGINE CONTROL section.
2. Check injector for leaks. See DIESELING, RUN-ON. Check fuel pressure. See FUEL SYSTEM PRESSURE TEST. On 2.8L engine, check A/C signal to pin "B8". Check air management system for intermittent air to ports while in closed loop.
3. 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. 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. On 2.8L and 4.3L engines, check EGR valve operation. See CHART C-7 in GENERAL MOTORS COMPUTER COMMAND CONTROL article in COMPUTERIZED ENGINE CONTROL 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 CHART C-1E in GENERAL MOTORS COMPUTER COMMAND CONTROL article in COMPUTERIZED ENGINE CONTROL 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 CHART C-10 (2.5L) or CHART C-10B (2.8L) in GENERAL MOTORS COMPUTER COMMAND CONTROL article in COMPUTERIZED ENGINE CONTROL 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 CHART C-7 (2.8L and 4.3L ) or CHART C-7A (2.5L) in GENERAL MOTORS COMPUTER COMMAND CONTROL article in COMPUTERIZED ENGINE CONTROL section.
2. Check ignition timing. Check fuel filter for restrictions. Check fuel pressure. Check alternator output voltage. Repair if less than 9 volts or more than 16 volts.
3. 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 2.8L and 4.3L engine, fuel pressure is relieved and drops to zero when ignition is turned off. On 2.5L engine, remove "FUEL PUMP" fuse from fuse block.
2. 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.

FUEL SYSTEM PRESSURE TEST

1. Turn engine off and relieve fuel pressure. See FUEL SYSTEM PRESSURE RELIEF. Remove air cleaner and plug air cleaner (THERMAC) vacuum port on throttle body.
2. Disconnect fuel line between throttle body and fuel filter. Install Fuel Pressure Gauge (J-29658) between throttle body and 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-5 (2.8L and 4.3L) or CHART A-7 (2.5L) in GENERAL MOTORS COMPUTER COMMAND CONTROL article in COMPUTERIZED ENGINE CONTROL section.
4. After testing, relieve fuel pressure. Remove fuel pressure gauge and install fuel line between filter and throttle body. Start vehicle and watch for leaks. Remove plug from throttle body vacuum port and install air cleaner.

Removal & Installation

Locate coolant temperature sensor. (Scheme 52) Disconnect battery negative cable. Drain coolant below level of sensor. Disconnect electrical connector and remove sensor. Handle CTS with care to prevent damage to sensor calibration. To install, reverse removal procedure.

Locate electronic control module under dash. (Scheme 52) Disconnect battery negative cable. Disconnect 2 electrical connectors from ECM. Remove ECM mounting hardware and ECM. To install, reverse removal procedure.

1. Relieve fuel system pressure. See 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.

Locate fuel pump relay. (Scheme 52) 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.

Locate MAP sensor on air cleaner. (Scheme 52) Disconnect vacuum tube and wiring from MAP sensor. Remove air cleaner cover and MAP sensor bracket retaining clip. Remove MAP sensor from bracket. To install, reverse removal procedure.

1. Locate oxygen sensor. (Scheme 52) 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 a liquid graphite Anti-Seize Compound (Part No. 3613695), containing glass beads. Tighten sensor to 30 ft. lbs. (41 N.m).

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

Removal

1. Remove air cleaner assembly. Disconnect throttle linkage, return spring and cruise control linkage (if equipped). Disconnect and identify all electrical connectors from throttle body.
2. Disconnect and identify all vacuum hoses from throttle body for installation reference. Relieve fuel pressure. See «FUEL SYSTEM PRESSURE RELIEF»(/gmc/cab-chassis-s15/1985-1988/remont/testing-diagnostics/#fuel-injection-system-tbi__fuel-system-pressure-relief) . Disconnect fuel lines from throttle body. Remove throttle body mount bolts and nut (if used). Remove throttle body.

Installation

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

Remove air cleaner assembly. Disconnect electrical connector from TPS sensor. Remove attaching screws, lock washers, retainers, and TPS sensor. To install, reverse removal procedure. Make sure TPS pick-up lever is ABOVE tang on throttle actuator lever. Use Loctite on TPS attaching screws.

ADJUSTMENTS

Note. See appropriate article in TUNE-UP section.

Fuel Meter Cover

1. Place throttle body assembly on Holding Fixture (J-9789) to prevent damage to throttle valves. Remove cover attaching screws and lock washers. Disconnect electrical leads from fuel injector(s).
2. Lift off fuel meter cover with fuel pressure regulator assembly attached. DO NOT remove fuel meter cover gasket at this time. Remove fuel pressure regulator dust seal from fuel meter body.

Fuel Injector

1. With fuel meter cover gasket in place, use a screwdriver to carefully pry injector(s) away from fuel meter body. Carefully lift injector(s) out with a twisting motion. (Scheme 54)
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.

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 idle air control valve using a 1-1/4" (32 mm) wrench.

Throttle Body Injection Component Locations. Scheme 52

Removing Fuel Meter Cover Assembly. Scheme 53

Note. Do not remove fuel meter cover gasket at this time.

Removing Fuel Injector Assembly. Scheme 54

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 that valve extends from motor housing. Measure from gasket mounting surface to end of pintle. Distance should not exceed 1-1/8" (28 mm). (Scheme 55)
2. On air control valve with collar on electrical connector, exert firm pressure on pintle while moving pintle from side to side until distance is correct.
3. On 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.
4. Invert throttle body assembly and place on clean, flat surface. Install idle air control valve and gasket. Tighten valve to 13 ft. lbs. (18 N.m). Place throttle body on holding fixture.
5. Install throttle position sensor. Make sure throttle position sensor pick-up lever is ABOVE tang on throttle actuator lever. Use Loctite on throttle position sensor attaching screws.

Installing Idle Air Control Valve. Scheme 55

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. Tighten screws to 35 INCH lbs (4 N.m). 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. Tighten screws to 28 INCH lbs. (3 N.m).

Exploded View of Throttle Body Assembly. Scheme 56

TORQUE SPECIFICATIONS

TORQUE SPECIFICATIONS

See also:
• TROUBLE SHOOTING
• FUEL SYSTEM PRESSURE RELIEF