Fuel Injection System - Pfi Buick Electra Estate Wagon

COMPONENT TESTING

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

DESCRIPTION

All General Motors models with Port Fuel Injection (PFI) systems have fuel delivery controlled by an on-board computer, the electronic control module (ECM). The ECM monitors engine operations and environmental conditions. It generates output signals to provide the correct air/fuel mixture, ignition timing and engine idle speed.

Standard PFI systems feature simultaneous double-fire injection. On these systems, all injectors pulse once each engine revolution. Thus, 2 injections of fuel are mixed with incoming air to produce the charge for each combustion cycle. On Buick Riviera and Buick Regal, the injectors are pulsed sequentially (1-by-1) in spark plug firing order. This system is referred to as Sequential Fuel Injection (SFI). Camaro and Corvette PFI system is referred to as Tuned Port Injection (TPI).

All 3 systems maintain constant fuel pressure to the injectors. Therefore, air/fuel ratio is adjusted by varying injector pulse width ("on" time). The ECM processes information from various sensors to compute the pulse width. There are 2 major sub-systems; the fuel system and the electronic control system. The mechanical portion of the port fuel injection system consists of fuel injectors, throttle body, fuel rail, fuel pressure regulator, idle air control (IAC) valve, fuel pump and fuel pump relay.

Note. Primary sub-systems affecting fuel system operation are covered in this article. Because of interrelated functions of Computer Command Control (CCC) system, refer to GENERAL MOTORS COMPUTER COMMAND CONTROL article in COMPUTERIZED ENGINE CONTROLS section for more information.

FUEL SYSTEM

The fuel system provides a constant, pressurized supply of clean fuel to the cylinder intake port injectors. The fuel system consists of the throttle body, fuel tank, in-tank electric fuel pump, fuel pump relay, fuel pressure regulator, in-line fuel filter, fuel rail, injectors, and Idle Air Control (IAC) valve.

ELECTRONIC CONTROL SYSTEM

The electronic control system monitors engine operating conditions, processes the information, and controls the engine for optimum performance and minimum emissions.

Input signals are generated by the Engine Coolant Temperature (ECT) sensor, Mass Air Flow (MAF) sensor, Exhaust Oxygen (O2) sensor, Throttle Position (TPS) sensor, Park/Neutral (P/N) switch, and Vehicle Speed sensor (VSS). Sunbird and Skyhawk 1.8L turbo and Fiero V6 use Manifold Air Temperature (MAT) sensor and Manifold Absolute Pressure (MAP) sensor instead of Mass Air Flow Sensor.

The ECM also receives signals from the starter solenoid (1.8L 4-cylinder models during cranking mode only), the air conditioner selector switch, and the ignition distributor.

FUEL CONTROL SYSTEM

The fuel control system starts with the fuel in the fuel tank. An electric fuel pump, located in the fuel tank with the gauge sending unit, pumps fuel to the fuel rail through an in-line fuel filter. The pump is designed to provide fuel at a pressure above the pressure needed by the injectors.

A pressure regulator in the fuel rail keeps fuel available to the injectors at a constant pressure. Unused fuel is returned to the fuel tank by a separate line. In order for the fuel injectors to supply a precise amount of fuel at the command of the ECM, the fuel supply system maintains a constant pressure of approximately 35 psi (2.5 kg/cm 2 ) drop across the injectors.

As manifold vacuum changes, the fuel system pressure regulator controls the fuel supply pressure to compensate. The fuel pressure accumulator, used on selected applications, isolates fuel line noises. The fuel rail is bolted rigidly to the engine. It provides the upper mount for the injectors. It also contains a spring-loaded pressure tap for testing the fuel system.

2.8L Port Fuel Injection System Diagram. Scheme 20

FUEL PUMP

Fuel is supplied to the system from an in-tank positive displacement roller vane pump. The pump supplies fuel through the in-line fuel filter to the fuel rail assembly. The pump is removed for service along with the fuel gauge sending unit. Once removed from the tank, the pump and sending unit are serviced separately.

Fuel pressure is achieved by rotation of the armature driving roller vane components. The impeller at the inlet end serves as a vapor separator and a prechange for the roller vane assembly. The unit operates at approximately 3500 RPM.

The pressure relief valve in the fuel pump will control fuel pump to 60-90 psi (2.1-6.3 kg/cm 2 ) maximum pressure. The fuel pump delivers more fuel than the engine can consume even under the most extreme conditions. Excess fuel flows through the pressure regulator and back to the tank via the return line.

The constant flow of fuel means that the fuel system is always supplied with cool fuel, thereby preventing the formation of fuel vapor bubbles. When the key is first turned on without the pump running, the ECM will turn the fuel pump relay on for 2 seconds. This builds up the fuel pressure quickly. If the engine is not started within 2 seconds, the ECM will shut the fuel pump off and wait until the engine starts.

As soon as the engine is cranked, the ECM will turn the relay on and run the fuel pump. As a back-up system to the fuel pump relay, the fuel pump can also be turned on by the oil pressure switch. The oil pressure switch is a normally open switch which closes when oil pressure reaches about 4 psi (.30 kg/cm 2 ). If the fuel pump relay fails, the oil pressure switch will close and run the fuel pump. An inoperative fuel pump relay can result in long cranking times, particularly if the engine is cold. (Scheme 21)

In-Tank Roller Vane Fuel Pump. Scheme 21

FUEL PRESSURE REGULATOR

The fuel pressure regulator contains a pressure chamber separated by a diaphragm relief valve assembly with a calibrated spring in the vacuum chamber side. Fuel pressure is regulated when pump pressure acting on the bottom side of the diaphragm overcomes the force of the spring action on the top side.

The diaphragm relief valve moves, opening or closing an orifice in the fuel chamber to control the amount of fuel returned to the fuel tank. The fuel pressure regulator maintains a constant 43.5 psi (3.0 kg/cm 2 ) pressure across the fuel injectors at all manifold depressions.

Vacuum acting on the top side of the diaphragm along with spring pressure controls the fuel pressure. An increase in vacuum creates a decrease in fuel pressure. Under heavy load conditions, the engine requires more fuel flow. Vacuum decreases under heavy load conditions because of throttle opening. A decrease in vacuum allows more pressure to the top side of the pressure relief valve, thus increasing fuel pressure. (Scheme 22)

Note. The SFI turbo engine pulses only 1 injector at a time, thus the fuel pressure drop is small. Therefore, the SFI system does not use a fuel pressure accumulator.

Sectional View of Fuel Pressure Regulator. Scheme 22

FUEL RAILS

The extruded fuel rail assembly includes a fuel pressure regulator, the 6 individual high pressure fuel injectors, and the cold start injector. The fuel rail assembly seats in the "V" between the upper plenum and the crossover runner section. The injectors fit into individual sockets in the base plate. The fuel rails used on 1.8L, 3.0L and 3.8L engines are manufactured, assembled and flow tested with the injectors as an assembly.

The injectors are force fit into the opening on the rail and a retainer clip is pushed into its locked position. (Scheme 23) The injectors are locked in place with the aid of the injector retainer clip which must be rotated in the proper direction.

Fuel Rails for 2.8L, 5.0L and 5.7L Engines. Scheme 23

FUEL INJECTORS

A fuel injector is installed in the intake manifold at each cylinder. Mounting is approximately 1.7-2.5" (70-100 mm) from the center line of the intake valve on V6 and V8 applications. Nozzle spray pattern is on a 25° angle. There are 2 "O" ring seals used. The lower "O" ring seals the injector at the intake manifold.

The "O" rings are lubricated and replaced as necessary whenever the injector is removed from the intake manifold. The "O" rings provide thermal insulation, thus preventing the formation of vapor bubbles and promoting good hot start characteristics. The "O" rings also prevent excessive injector vibration.

Air leakage at the injector/intake area would create a lean cylinder and possibly a driveability problem. A second seal is used to seal the injector to the fuel rail connection. (Scheme 24) The injectors are identified with an ID number cast on the injector near the top side. Injectors manufactured by Rochester Products have an "RP" positioned near the top side in addition to the ID number.

The solenoid-operated injector consists essentially of a valve body and a nozzle valve which has a special ground pintle. The movable armature is attached to the nozzle valve which is pressed against the nozzle body sealing seat by a helical spring. At the back of the valve body is the solenoid winding and in the front section is the guide for the nozzle valve.

Each injector has a 2-wire connector. On 3.0L and 3.8L motors, the engine connectors have a spring clip that must be released (unlocked) before removal of the connector. One wire supplies voltage from the fuse(s) in the fuse panel. The second wire connects to the ECM, which controls the ground to operate the injectors (pulse width).

The electric pulses generate a magnetic field in the solenoid winding. As a result, the armature is drawn back and lifts the nozzle valve from its seat approximately .038" (.15 mm). The helical spring closes the nozzle valve.

Typical Fuel Injector. Scheme 24

Note. Because of the sequential pulsing of the turbocharged V6 injectors, the wiring harness MUST be connected to the proper injector. The Brown wire is the "B" positive feed to all 6 injectors. The ECM ground circuit for each injector is color coded differently for identification.

COLD START VALVE

The cold start valve is used to provide additional fuel during the crank mode to improve cold start-ups. This circuit is important when engine coolant temperature is low because the other injectors are not pulsed on long enough to provide the needed amount of fuel to start the engine.

The circuit is activated only in the crank mode. The power is supplied directly from the starter solenoid and is protected by a fuse. The system is controlled by a thermal time switch which provides a ground path for the valve during cranking when engine coolant temperature is below 95°F (35°C).

The thermal switch is made of a bi-metallic material which opens at a specified coolant temperature. This bi-metallic material is also heated by the winding in the thermal switch, allowing the valve to stay on for 8 seconds at 68°F (20°C) coolant temperature.

The time the thermal switch will stay closed varies inversely with coolant temperature. As the coolant temperature goes up, the cold start valve "on" time goes down.

AIR INDUCTION SYSTEM

Air is drawn into the induction system through an air pick-up mounted in front of the radiator support. This arrangement insures that initial air pick-up is outside the high temperatures of the engine compartment resulting in denser air charges to the combustion chambers.

The air cleaners have replaceable paper elements that are designed for 30,000 mile change intervals. The smooth blend of the air duct system is essential and provides an air flow free of turbulence into the MAF sensor to insure accurate air measurements. Since the amount of air entering the induction system is measured by the MAF sensor only, any air that entered behind the MAF sensor would not be measured and would be unknown to the computer.

The rubber boot between the MAF sensor and throttle body assembly seals these units and prevents air leaks that could not be detected, and could possibly provide an air/fuel ratio too lean for proper engine operation. The boot also isolates engine movement from the MAF sensor and air duct system.

THROTTLE BODY

The throttle body is used to control the amount of air that enters the engine as well as the amount of vacuum in the throttle body vacuum manifold. The throttle body also supports and controls the movement of the throttle position sensor (TPS), enabling the ECM to know the throttle position under all operating conditions. (Scheme 25)

Exploded View of Typical Throttle Body. Scheme 25

IDLE AIR CONTROL

The idle air control (IAC) valve controls engine idle speed, while preventing stalls due to changes in engine load. The IAC valve, mounted in the throttle body, controls by-pass air around the throttle valve. By moving a conical valve in (decreasing air flow) or out (increasing air flow), a controlled amount of air can move around the throttle plate.

If RPM is too low, more air is by-passed around the throttle plate. If RPM is too low, more air is by-passed around the throttle valve to increase RPM. If RPM is too high, less air is by-passed around the throttle valve to decrease RPM. The IAC valve moves in small steps called "counts", which can be measured by test equipment which plugs into the ALCL.

During idle, the proper position of the IAC valve is calculated by the ECM based on battery voltage, coolant temperature, engine load, and engine RPM. If the RPM drops below a specified RPM, and the throttle plate is closed, the ECM senses a near stall condition. The ECM will then calculate a new valve position to prevent stalls.

If the IAC valve is disconnected and reconnected with the engine running, the idle RPM may be wrong. In this case, the IAC has to be reset. On vehicles equipped with 3.0L engines, the IAC resets when the ignition is turned from the "ON" to "OFF" position. When servicing the IAC, it should only be disconnected or connected with the ignition off.

This prevents having to reset the IAC. Different designs are used for the IAC valve. Be sure to use the correct design when replacement is required. The IAC valve affects only the idle characteristics of the vehicle. If it is open fully, too much air will be allowed into the manifold and idle speed will be high.

If IAC valve is stuck closed, too little air will be allowed in the manifold, and idle speed will too low. If it is stuck part way open, the idle may be rough, and will not respond to engine load changes.

Speed Density (1.8L Turbo & Fiero 2.8L Only)

The speed density technique of computing airflow rate is used on Skyhawk and Sunbird 1.8L turbocharged engines and Fiero with 2.8L V6 engines. Manifold absolute pressure and temperature along with maps or estimates of engine variables are used to calculate airflow in the ECM. The manifold absolute pressure (MAP) sensor to responds to changes in manifold pressure (vacuum) resulting from engine load and speed changes.

The ECM sends a reference voltage signal to the MAP sensor. As manifold pressure changes, the resistance of the MAP sensor changes. By monitoring sensor output voltage, the ECM determines manifold pressure. If the MAP sensor fails, the ECM will substitute a fixed MAP value and use the throttle position sensor (TPS) to control fuel.

Mass Air Flow

The mass air flow system uses a single sensor to compute measurement of mass air flow. Mass air flow is derived by processing the MAF sensor signal through a look-up table programmed into the ECM. A typical MAF sensor consists of a screen to break up air flow, a resistor, a heated film, and electronic module mounted on the sensor.

Air flow is directed over the heated film. The cooling effect of air flowing over the heated film in the sensor changes its resistance. Additional electrical power is then required to maintain the sensor at 165° (75°C) above the incoming air temperature. This current is measured and converted to a digital signal (30-150 Hz) that is sent to the vehicle's ECM.

The ECM uses the signal to calculate air intake in grams per second through preprogrammed information. Using calculations of mass air flow, engine temperature and RPM, the ECM calculates the exact amount of fuel required to provide a proper air/fuel ratio (14.7:1). The MAF sensor readings and fuel requirement calculations are made by the computer every 6-14 milli-seconds (approximately 160 calculations per second). (Scheme 26)

Exploded View of Mass Air Flow Sensor. Scheme 26

ADJUSTMENTS

Note. For all on-vehicle adjustments, see appropriate TUNE-UP article.

MINIMUM IDLE SPEED

Note. This adjustment should be necessary only when throttle body parts have been replaced or when required by TPS adjustment. Engine should be at normal operating temperature.

1.8L 4-Cylinder

1. Disconnect PCV hose to cause a severe vacuum leak and substantial increase in idle speed. Wait 2 minutes and disconnect IAC electrical connector.
2. Reconnect PCV hose. Set minimum idle rate to 675-725 RPM with automatic transmission, and 700-750 RPM with manual transmission. Reconnect IAC connector. IAC will reset when vehicle is driven over 45 MPH.

2.8L, 3.0L & 3.8L V6 With Multi-Port Fuel Injection

1. Pry out idle stop screw plug in throttle body. With IAC motor connected, ground diagnostic lead "B" on diagnostic connector (ALDL). Diagnostic connector is behind left side of instrument panel near steering column.
2. Connect tachometer to engine. Turn on ignition, but do not start engine. Wait at least 30 seconds. With ignition on, disconnect IAC connector. Remove ground from diagnostic lead and start engine.
3. Adjust idle set screws to 500-600 RPM in Drive on 2.8L engines (600-700 RPM in Neutral for manual transmissions). On 3.0L and 3.8L engines, set idle speed to 450-550 RPM in Drive.
4. Turn ignition off and reconnect connector at IAC motor. Adjust TPS to .55 volts on 2.8L and 3.0L engines. On 3.8L engines, adjust TPS to .40 volts. Start engine and check for proper idle operation.

5.0L & 5.7L V8

1. Pierce the idle stop screw plug with an awl, and remove plug. With IAC motor connected, ground diagnostic lead.
2. Turn on ignition, do not start engine. Wait at least 30 seconds. With ignition on, disconnect IAC electrical connector. Remove ground from diagnostic lead and start engine. Allow engine to closed loop.
3. Adjust idle stop screw to 400 RPM in drive on automatic transmission and to 450 RPM with manual transmission. Turn ignition off and reconnect connector at IAC motor.
4. Adjust TPS to .62 volt. Secure TPS and recheck voltage. Start engine and inspect for proper idle operation.

REMOVAL & INSTALLATION

Removal

Turn ignition off. Unplug injector electrical connectors. Relieve fuel system pressure. Disconnect fuel lines at fuel rail. Remove fuel rail bracket mounting screws and lift off fuel rail. Remove injectors.

Installation

To install, reverse removal procedure. Use new "O" rings on injectors.

Unplug electrical connector from IAC valve. Remove IAC valve from throttle body using a 1 1/4" wrench.

Scheme 27

1. Before installing new IAC valve measure the distance that the valve is extended. If cone is extended too far, valve may be damaged when installed. Distance must be no greater than 1 1/8" (28 mm).
2. Measurement should be taken from motor housing flange to end of cone. Determine if IAC valve is Type I or Type II. Type I has a collar at electrical terminal, Type II does not. (Scheme 27) (Scheme 27): Identifying IAC Valve
3. To retract Type I, exert firm pressure on valve. For Type II, compress retaining spring from valve while turning "in" with a clockwise motion. Return spring to original position.
4. For both type valves, install valve with new gasket. Tighten to 13 ft. lbs. (18 N.m). Install connector on valve. Start engine. ECM will reset idle speed when vehicle is driven at 30 MPH.

O2 sensor may be difficult to remove when engine temperature is below 120°F (48°C). Disconnect negative battery cable. Unplug O2 sensor electrical connector. Remove O2 sensor.

1. O2 sensor threads must be coated with special anti-seize compound before installation. New sensors will have compound applied to threads.
2. If old sensor is to be reinstalled, coat with anti-seize compound (5613659). Tighten to 30 ft. lbs. (41 N.m).

Unplug electrical connector from TPS. Remove and discard 2 TPS retaining screws. Remove TPS sensor. If necessary, remove screw holding TPS actuator lever to end of throttle shaft.

1. With throttle valve in closed idle position, install TPS on throttle body assembly. TPS pick-up lever must be above tang on throttle actuator lever. Install new screws with thread locking compound.
2. On 1.8L, tighten screws and install connector. On 3.8L, TPS must be adjusted before tightening screws. See appropriate article in TUNE-UP section.

Removal & Installation - Except Corvette

1. Disconnect negative battery cable. Remove pressure from fuel lines as described in the caution under «REMOVAL & INSTALLATION»(/buick/electra-estate-wagon/1985-1985/remont/testing-diagnostics/#fuel-injection-system-pfi__removal-installation) . Lower fuel tank. Remove fuel lever sending unit and pump assembly by turning cam lock ring counterclockwise. Lift assembly from fuel tank and remove fuel pump from fuel lever sending unit.
2. Pull 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.

Removal (Corvette)

1. Relieve fuel system pressure. Remove fuse marked "Fuel Pump" from fuse block in passenger compartment. Crank engine. Engine will start and run until fuel in line is exhausted. When engine stops, engage starter again for 3 seconds to ensure engine will not start.
2. Remove battery ground cable. Remove fuel cap, fuel tank filler door. Remove filler neck housing and disconnect drain hose. Remove screws attaching fuel meter and pump assembly to tank. Disconnect fuel hoses, vapor hose and electrical connector from fuel meter and pump assembly. Pull pump up into pulsator while pulling outward away from bottom support. Remove pump.

Reverse removal procedure, using new gasket.

Scheme 28

1. The ECM receives signals from sensors concerning engine operating conditions. If the sensor reading is not what it should be, the ECM will turn on the "CHECK ENGINE" light on the instrument panel, and will store a trouble code in the memory.
2. To obtain a stored trouble code from the ECM, the assembly line communication link (ALCL) is used. ALCL is located in passenger compartment. To enter the diagnostic mode, connect test terminal (terminal B) to terminal A or ground with the engine stopped. (Scheme 28) (Scheme 28): ALCL Connector
3. The ECM will first display a code "12" to indicate the system is operating. Code are displayed by flashing the "CHECK ENGINE" light. Code 12 consists of a flash, followed by a short pause, then 2 quick flashes in succession.
4. Other codes are displayed in a similar manner. Each code will be displayed 3 times. Codes can be cleared from the ECU memory by disconnecting the ECU harness from positive battery pigtail for 10 seconds with ignition off. The following codes indicate these problems

Code 13

Oxygen sensor circuit failed.

Code 14

Coolant sensor reading too high.

Code 15

Coolant sensor reading too low.

Code 21

Throttle position sensor reading too high.

Code 22

Throttle position sensor reading too low.

Code 23

Manifold air temperature too low.

Code 24

Vehicle speed sensor failed.

Code 25

Manifold air temperature sensor too high.

Code 31

Wastegate electrical signal open or grounded.

Code 33

MAF sensor reading too high.

Code 34

MAF sensor reading too low or no signal.

Code 41

Cylinder select error.

Code 42

Error in distributor.

Code 43

Electronic spark control failure.

Code 44

Oxygen sensor lean too long.

Code 45

Oxygen sensor rich too long.

Code 51

Calibration PROM error.

Code 52

CALPAK unit missing.

Code 53

Over voltage condition.

Code 54

Low fuel pump voltage.

Code 55

Internal ECM error.

PRELIMINARY CHECKS

Prior to diagnosing the fuel injection system, the following systems and components must be in good condition and operating properly

1. All support systems and wiring.
2. Battery connections and specific gravity.
3. Compression pressure.
4. Fuel supply system pressure and flow.
5. All electrical connections.
6. Air filter.
7. Vacuum lines, fuel hoses and pipe connections.

FUEL SYSTEM DIAGNOSIS

Note. Wrap a shop towel around the fuel pressure tap to absorb any small amount of fuel leakage that may occur when installing the gauge.

1. Connect fuel pressure gauge (J 34730 1) to fuel system. Turn ignition on. Fuel pump pressure should be 37-43 psi (2.6-3.0 kg/cm 2 ). This pressure is controlled by spring pressure within the regulator assembly.
2. When the engine is idling, the manifold pressure is low (high vacuum) and is applied to the fuel regulator diaphragm. This will offset the spring and result in a lower fuel pressure of 35-38 psi (2.5-2.7 kg/cm 2 ).
3. The idle pressure will vary some depending on barometric pressure. If the pressure at idle is less than 35 psi (2.5 kg/cm 2 ) this indicates a problem with the pressure regulator control.
4. If fuel is observed in vacuum hose to pressure regulator, the regulator is faulty and must be replaced. Pressure that continues to fall is caused by 1 of the following: In-tank fuel pump check valve not holding, pump coupling hose leaking, fuel pressure regulator valve leaking or a injector sticking open.
5. If regulated pressure is less than 37 psi (2.6 kg/cm 2 ), the amount of fuel to the injectors is okay but pressure is too low. System will be lean running and may set code 44 and also cause hard starting cold and overall poor performance.

Restricted Flow

1. Normally, a vehicle with a fuel pressure of less than 24 psi (1.7 kg/cm 2 ) at idle will not be driveable. However, if the pressure drop occurs only while driving, the engine will normally surge and then stop as pressure begins to drop rapidly.
2. Restricting the fuel return line allows the fuel pump to develop its maximum pressure (dead head pressure). When battery voltage is applied to the pump test terminal, pressure should be above 75 psi (5.3 kg/cm 2 ). Test system to determine if the high fuel pressure is due to a restricted fuel return line or a pressure regulator problem.

HARD START

Note. If engine starts but dies immediately, see ENGINE CRANKS BUT WON'T RUN diagnostic chart.

1. Check fuel pump relay by probing fuel pump test terminal with a test light to ground. Turn ignition off for 10 seconds, then turn the ignition on. Test lamp should light for 2 seconds.
2. If it does not light, check TPS for sticking or binding. Check injectors for leaking. Check for high resistance in coolant sensor circuit or sensor itself.
3. Check for faulty in-tank fuel pump check valve. See Fuel System Diagnosis Chart.

3.0L, 3.8L, 5.0L & 5.7L Engines

1. Check fuel pump relay: Probe fuel pump test terminal with a test light to ground. Turn ignition off for 10 seconds, then turn the ignition on. Test lamp should light for 2 seconds. If it does not light, fuel pump relay is at fault.
2. Check TPS for sticking or binding. Check for high resistance in coolant sensor circuit or sensor itself. Check for faulty in-tank fuel pump check valve. To check, turn ignition off.
3. Disconnect fuel pressure line at fuel rail. Remove tank filler cap. Connect a radiator test pump to the line and apply 15 psi (1.05 kg/cm 2 ). If pressure holds for 60 seconds, check valve is okay.

All Exc. 3.0L & 3.8L V6

1. Check for proper operation of IAC system. See Idle Air Control Test chart. Check for plugged or restricted fuel lines. See Fuel System No Pressure Test chart.
2. Check for proper operation of PCV valve. On all 3.8L V6 engines, check for air leaks at air duct between MAF sensor and throttle body, and check for proper EGR operation.

1. Check fuel pressure. See Fuel System Diagnosis chart. Check for water contaminated fuel. Check TPS for sticking or binding. Check vacuum hose to MAP sensor for cuts or restrictions.
2. Check alternator output voltage. If less than 9 volts or more than 16 volts, repair. Check canister purge system for proper operation.

3.0L & 3.8L V6

1. Check for proper seal of oil filler cap and tube. Check fuel pressure. See Fuel System Diagnosis chart. Check for water contaminated fuel. Check for air leaks at air duct between MAF sensor and throttle body.
2. Check TPS for sticking or binding. Check alternator output voltage. If less than 9 volts or more than 16 volts, repair. Check canister purge system for proper operation. Check EGR system for valve sticking intermittently.

ROUGH, UNSTABLE IDLE

1. Check throttle linkage for sticking. Check idle speed. Check IAC system. See Idle Air Control Test chart. Check alternator output voltage. Repair if less than 9 volts or more than 16 volts.
2. Check injector balance. See Injector Balance Check chart. On all 3.8L V6 engines, check EGR. There should be no EGR at idle.
3. On all engines, inspect O2 sensor for silicon contamination from fuel or improper use of RTV sealant. Sensor is defective if it is coated with a white, powdery coating.

CUTS OUT, MISSES

Check injector balance. See Injector Balance Check chart. Check for restricted fuel filter and water in tank. Check for low fuel pressure. See Fuel System Diagnosis chart.

DETONATION

Improper fuel octane rating. Check for high fuel pressure caused by defective fuel pressure regulator.

Engine Cranks But Will Not Run (1.8L 4-Cylinder Turbo). Scheme 29

Fuel System No Pressure Check. Scheme 30

Fuel System Diagnosis. Scheme 31

Engine Cranks But Will Not Run (1.8L 4-Cylinder Turbo). Scheme 32

Engine Cranks But Will Not Run (3.8L V6 Non-Turbo). Scheme 33

Engine Cranks But Will Not Run (3.8L V6 Turbo). Scheme 34

Wastegate Functional Check (1.8L 4-Cylinder Turbo). Scheme 35

Idle Air Control Testing. Scheme 36

Injector Balance Test. Scheme 37

SPECIFICATIONS

Note. Specifications not available. Refer to specifications within appropriate REMOVAL & INSTALLATION or ADJUSTMENTS subject in this article.

Wiring Diagram for 1.8L Turbo Fuel Injection System. Scheme 38

Wiring Diagram for 2.8L V6 Fuel Injection System (All Except Fiero Models). Scheme 39

Wiring Diagram for 2.8L V6 Fuel Injection System (Fiero Models). Scheme 40

Wiring Diagram for 3.8L V6 Fuel Injection System (Non-Turbo Models). Scheme 41

Wiring Diagram for 3.8L V6 Fuel Injection System (Turbo Models). Scheme 42

Wiring Diagram for 5.0L & 5.7L V8 Fuel Injection System. Scheme 43

See also:
• REMOVAL & INSTALLATION
• ADJUSTMENTS