Fuel Injection System - Pfi — Pontiac 6000 I (1982-1991)

COMPONENT TESTING

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

DESCRIPTION

All General Motors vehicles with Port Fuel Injection (PFI) systems have fuel delivery controlled by an on-board computer, the Electronic Control Module (ECM). The ECM monitors engine operating and environmental conditions. It generates output signals to provide the correct air and 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 Century, Ciera, Delta 88, Electra, Ninety-Eight, Regal, Regency and Toronado models, the injectors are pulsed sequentially (1-by-1) in spark plug firing order. One injection of fuel for every combustion cycle. 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, the air and fuel ratio is adjusted by varying injector pulse width, or injector 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 COMPUTER COMMAND CONTROL article in COMPUTER 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 these conditions, and then controls the engine for optimum performance and minimum emissions.

Input signals are generated by the Engine Coolant Temperature (ECT) sensor, Mass Airflow (MAF) sensor, Exhaust Oxygen (O2) sensor, Throttle Position Sensor (TPS), Park and Neutral switch, and Vehicle Speed Sensor (VSS). Sunbird and Skyhawk 1.8L turbo and Fiero 2.8L use Manifold Air Temperature (MAT) sensor and Manifold Absolute Pressure (MAP) sensor instead of MAF sensor.

The ECM also receives signals from the starter solenoid, the air conditioner selector switch and the ignition distributor.

FUEL CONTROL SYSTEM

The basic function of the fuel control system is to control fuel delivery to the engine. Fuel is delivered to the engine by individual fuel injectors mounted in the intake manifold near each intake valve. The main control sensor of this system is the O2 sensor. The O2 sensor tells the ECM how much oxygen is in the exhaust gas. The ECM then changes the air and fuel ratio to the engine by controlling the injector on time.

The fuel control system is made up of the following parts: fuel injectors, throttle body, fuel rail, fuel pressure regulator, idle air control valve, fuel pump and fuel pump relay. The fuel control system starts with the fuel in the fuel tank. An electric fuel pump, located in the fuel tank with the fuel 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 return 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 34-46 psi (2.4-3.2 kg/cm 2 ) drop across the injectors. When the ignition is turned on, the ECM will turn on the in-tank fuel pump. It will remain on as long as the engine is cranking or running. It senses this from distributor reference pulses.

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 pressure.

2.8L Port Fuel Injection System Diagram This diagram is a basic representation of all GM PFI systems. Scheme 32

Scheme 32: 2.8L Port Fuel Injection System Diagram This diagram is a basic representation of all GM PFI systems.

FUEL PUMP

Fuel is supplied to the system from an in-tank positive displacement roller vane fuel 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 the roller vane components. The impeller at the inlet end serves as a vapor separator and a precharge 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 on the fuel pump relay 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 on the relay 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 33)

Typical In-Tank Roller Vane Fuel Pump. Scheme 33

Scheme 33: Typical In-Tank Roller Vane Fuel Pump

FUEL PRESSURE REGULATOR

The fuel pressure regulator is a diaphragm-operated relief valve with injector pressure on one side and manifold pressure on the other. The function of the regulator is to maintain a constant pressure at the injectors at all times. Some models also use a fuel pressure accumulator to compensate for high fuel demand conditions. The pressure regulator also compensates for engine load by increasing fuel pressure when it sees low engine vacuum.

The pressure regulator is mounted on the fuel rail and is serviced separately. If pressure is too low, poor performance could result. If the pressure is too high, excessive odor and a code 45 may result. (Scheme 34)

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 34

Scheme 34: Sectional View of Fuel Pressure Regulator

FUEL RAILS

The extruded fuel rail assembly includes a fuel pressure regulator, 6 or 8 individual high pressure fuel injectors and 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 35) The injectors are locked in place with the aid of an injector retainer clip which must be rotated in the proper direction.

Fuel Rails for 2.8L, 5.0L and 5.7L Engines. Scheme 35

Scheme 35: Fuel Rails for 2.8L, 5.0L and 5.7L Engines

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. Nozzle spray pattern is on a 25° angle, in a conical pattern. There are 2 "O" ring seals used. The lower "O" ring seals the injector at the intake manifold. The upper "O" ring seals the injector to the fuel rail.

The "O" rings should be lubricated and replaced whenever the injector is removed from the intake manifold. These "O" rings also 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. (Scheme 36) The injectors are identified with an ID number cast in the injector near the top. Injectors manufactured by Rochester Products have an "RP" positioned near the top 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 moveable armature is attached to the nozzle valve which is pressed against the nozzle body sealing seat by a helical spring.

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, or on time.

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 36

Scheme 36: Typical Fuel Injector

Note. Because of the sequential pulsing of the injectors in SFI systems, the wiring harness must be connected to the proper injector. See WIRING DIAGRAMS in this article for proper connections.

COLD START VALVE

The cold start valve is used to provide additional fuel during the cold crank mode to improve cold start-ups. This circuit is important when engine coolant temperature is low. The main injectors are not pulsed long enough to provide the needed fuel to start the cold 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. The thermal time switch provides a ground path for the valve during cranking when engine coolant temperature is below 95°F (35°C).

The thermal time switch is made of a bi-metallic material which is heat sensitive and is controlled by one of 2 factors. When the coolant temperature is below 68°F (20°C), the switch is closed feeding power to the cold start injector. Yet this injector is limited to an 8 second on time interval. Therefore this thermal time switch also contains a heating element. If the coolant temperature does not rise above 68°F (20°C) in less than or equal to the 8 second period, the heating element will have at the same time have heated the switch enough for it to open within the prescribed time period. In either situation the switch will in no way in any condition actuate the cold start injector for longer than an 8 second period.

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 smooth blend of the air duct system is essential and provides an airflow 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 and fuel ratio which is 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 37)

Exploded View of Typical Throttle Body All models have similar parts in different configurations. Scheme 37

Scheme 37: Exploded View of Typical Throttle Body All models have similar parts in different configurations.

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 airflow) or out (increasing airflow), a controlled amount of air can move 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 plugged 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 value, and the throttle plate is closed, the ECM senses a near stall condition. The ECM will then calculate a new IAC valve position to prevent the stall.

If the IAC valve is disconnected and reconnected with the engine running, the idle RPM may be wrong and must be reset. On vehicles equipped with 3.0L engines, the IAC resets when the ignition switch is turned from the "ON" to the "OFF" position. On all other models, the IAC valve will reset when the vehicle is driven over 35 MPH. 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 fully open, too much air will be allowed into the manifold and the idle speed will be high.

If IAC valve is stuck closed, too little air will be allowed in the manifold and idle speed will be 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 engines. Manifold Absolute Pressure (MAP) and Manifold Air Temperature (MAT), along with estimates of engine variables are used to calculate airflow by the ECM. The manifold absolute pressure sensor responds to changes in manifold pressure (vacuum) resulting from engine load and RPM changes.

The ECM sends a 5-volt reference 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.

Note. The mass airflow method of determining airflow is used on all vehicles other than 1.8L turbos and Fiero 2.8L models.

Mass Airflow

The Mass Airflow (MAF) system uses a single sensor to determine airflow. Mass airflow is derived by processing the MAF sensor signal through a preprogrammed comparative data table in the ECM. A typical MAF sensor consists of a screen to break up airflow, a air temperature sending resistor, a heated film and electronic module mounted on the sensor.

Airflow 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°F (75°C) above the incoming air temperature. This current is measured and converted to a digital signal (30-150 Hz) which is then sent to the ECM. The ECM uses the signal to calculate air intake in grams per second. The ECM compares this signal with those stored in memory.

Using calculations of mass airflow, engine temperature and RPM, the ECM calculates the exact amount of fuel required to provide a proper air and 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 38)

Exploded View of Mass Airflow Sensor. Scheme 38

Scheme 38: Exploded View of Mass Airflow Sensor

ADJUSTMENTS

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

MINIMUM IDLE SPEED ADJUSTMENT

Note. This adjustment should be necessary only when the throttle body or throttle body parts have been replaced. All idle speeds, hot or cold, are controlled by the idle air control valve. Idle speeds will vary. This is considered normal.

Note. All 1.8L and Fiero 2.8L engines are not adjustable.

2.8L (Except Fiero), 3.0L & 3.8L

With IAC motor connected, ground diagnostic test lead. Turn ignition on, but do not start engine. Wait at least 30 seconds.
With ignition on, disconnect IAC electrical connector. Remove ground from diagnostic lead and start engine. Pierce the idle stop screw plug with an awl, and remove plug.
Adjust minimum idle speed screw to obtain an idle RPM of 500-600 RPM on automatic transmission 2.8L vehicles, 600-700 RPM on manual transmission 2.8L vehicles, 450-550 RPM on all 3.0 and 3.8L vehicles. (Scheme 37)

5.0L & 5.7L

Pierce the idle stop screw plug with an awl, and remove plug. With IAC motor connected, ground diagnostic lead.
Turn ignition on, but do not start engine. Wait at least 30 seconds. Disconnect IAC electrical connector. Disconnect the distributor set-timing connector. Start engine and allow to go to closed loop.
Remove ground from diagnostic connector. Adjust idle stop screw to 400 RPM in drive on automatic transmission and to 450 RPM in neutral with manual transmission. Turn ignition off and reconnect connector at IAC motor.
Adjust TPS to .62 volt. See «THROTTLE POSITION SENSOR ADJUSTMENT»(/pontiac/6000/i-1982-1991/remont/testing-diagnostics/#fuel-injection-system-pfi__throttle-position-sensor-adjustment) in this article.

THROTTLE POSITION SENSOR ADJUSTMENT

Note. Throttle position sensor on 1.8L and 2.8L Fiero models are not adjustable.

2.8L, 3.0L, 5.0L & 5.7L

Install 3 jumper wires between TPS and harness connector. On all models except those with 2.8 and 3.0L engines, remove 2 TPS hold-down screws and apply Loctite (262) to the threads and reinstall.
With ignition on, connect a digital voltmeter to "A" and "B" terminals of TPS connector. (Scheme 39) Adjust TPS output voltage in the closed idle position to.50-.60 volts on 2.8 and 3.0L engines,.47-.62 volts on 5.0 and 5.7L engines. Tighten screws and recheck the adjustment.

3.8L

Install 3 jumper wires between TPS and harness connector. With ignition on, connect a digital voltmeter to the "B" and "C" terminals of the TPS connector. (Scheme 39)
Adjust TPS in the closed idle position to obtain an output voltage of.35-.45 volts. Tighten screws and recheck adjustment.

Throttle Position Sensor Terminal Identification. Scheme 39

Scheme 39: Throttle Position Sensor Terminal Identification

REMOVAL & INSTALLATION

CAUTION

The fuel system is under pressure. Before servicing a fuel rail, pressure regulator or injector, relieve 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.

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 40

Scheme 40: Installation

Before installing new IAC valve, measure the distance that the valve is extended. (Scheme 40) If cone is extended too far, valve may be damaged when installed. Distance must be no greater than 1 1/8" (28 mm).
Measurement should be taken from valve housing flange to end of cone. Determine if IAC valve is Type I or Type II. Type I has a collar at electrical terminal and Type II does not. (Scheme 40) (Scheme 40): Identifying IAC Valve
To retract Type I, exert firm pressure on valve. To retract Type II, compress retaining spring while turning valve in with a clockwise motion. Return spring to original position.
Either valve should be installed with a 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 above 35 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.

O2 sensor threads must be coated with anti-seize compound before installation. New sensors will have compound applied to threads.
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.

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.
On 1.8L models and 2.8L Fiero, tighten screws and install connector. On all other models, TPS must be adjusted before tightening screws. See «THROTTLE POSITION SENSOR ADJUSTMENT»(/pontiac/6000/i-1982-1991/remont/testing-diagnostics/#fuel-injection-system-pfi__throttle-position-sensor-adjustment) in this article.

Removal & Installation (Except Corvette)

Disconnect negative battery cable. Relieve pressure from fuel lines. Lower fuel tank. Remove fuel level sending unit and pump assembly by turning cam lock ring counterclockwise. Lift assembly fuel tank and remove fuel pump from sending unit.
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)

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.
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.

DIAGNOSTIC TESTING

Note. For further diagnostic procedures and charts see COMPUTER COMMAND CONTROL article in COMPUTER CONTROLS section.

ECM TROUBLE CODES

The ECM receives signals from sensors concerning engine operating conditions. If the sensor reading is not what it should be, as compared to what is in memory, the ECM will turn on the "CHECK ENGINE" or "SERVICE ENGINE SOON" light on the instrument panel, and will store a trouble code in memory.

Scheme 41

Scheme 41: ENTERING DIAGNOSTIC MODE

To obtain a stored trouble code from the ECM, the Assembly Line Communication Link (ALCL) is used. The ALCL connector is located in the passenger compartment. To enter the diagnostic mode, connect diagnostic terminal (terminal B) to ground (terminal A) with the engine stopped. (Scheme 41) (Scheme 41): ALCL Connector
The ECM will first display a code "12" to indicate the system is operating. Codes are displayed by flashing either the "CHECK ENGINE" or "SERVICE ENGINE SOON" light. Code 12 consists of a single flash, followed by a short pause, then 2 quick flashes in succession.
Other codes are displayed in a similar manner. Each code will be displayed 3 times. After all codes have been displayed, the ECM will return to flashing code 12. It will flash code 12 until the diagnostic terminal is ungrounded.

TROUBLE CODE DEFINITIONS

The following codes indicate these problems.

Code 13

Oxygen sensor circuit open.

Code 14

Coolant sensor reading too low.

Code 15

Coolant sensor reading too high.

Code 21

Throttle position sensor signal voltage too high.

Code 22

Throttle position sensor signal voltage too low.

Code 23

Manifold air temperature circuit signal voltage high.

Code 24

Vehicle speed sensor failed.

Code 25

Manifold air temperature sensor circuit signal voltage low.

Code 31

Wastegate overboost condition.

Code 32

EGR system failure.

Code 33

MAF sensor signal voltage too high on 2.8L, 5.0L, and 5.7L engines. MAP sensor sensor signal voltage high on 1.8L and 3.0L engines.

Code 34

MAF sensor signal voltage too low or no signal on 2.8L, 5.0L and 5.7L engines. MAP sensor signal voltage voltage low on 1.8L and 3.0L engines.

Code 35

Idle air control failure.

Code 36

MAF sensor burn off function fault.

Code 41

Cylinder select error.

Code 42

Open or short to ground in the Electronic Spark Timing system or by-pass circuits.

Code 43

Electronic spark control voltage at ECM connector terminal B-7 low for at least 4 seconds.

Code 44

Oxygen sensor indicating lean exhaust.

Code 45

Oxygen sensor indicating rich exhaust.

Code 51

Calibration PROM error. Possible PROM connection short.

Code 52

Fuel CALPAK unit missing.

Code 53

Over voltage condition. Basic generator problem.

Code 54

Low fuel pump voltage.

Code 55

Possible internal ECM error. Check ECM grounds. If okay, replace ECM.

CLEARING TROUBLE CODES

Trouble codes should be cleared after repairs have been made. Also, some diagnostic charts will tell you to clear codes before using the chart. This allows the ECM to set the code while going through the chart, which will help to find the cause of the problem more quickly.

Turn ignition on and ground diagnostic test terminal at ALCL connector. Turn ignition off and remove ECM fuse from fuse block for 10 seconds or more. Remove test lead from ALCL connector.

EXITING DIAGNOSTIC MODE

When diagnosis is complete, exit diagnostic mode by disconnecting ground from diagnostic terminal.

PRELIMINARY CHECKS

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

All support systems and wiring.
Battery connections and specific gravity.
Compression pressure.
Fuel supply system pressure and flow.
All electrical connections.
Air filter.
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. FUEL SYSTEM DIAGNOSTIC charts can be found following the TROUBLE SHOOTING section. (Scheme 42)- (Scheme 60).

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.
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 ).
The idle pressure will vary 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.
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.
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 Fuel Flow

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.
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. For 1.8L engines (Scheme 42)- (Scheme 45). For 3.0L and 3.8L engines (Scheme 48)- (Scheme 51).

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. If it does not light, fuel pump relay is at fault.
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. See FUEL SYSTEM DIAGNOSIS chart. (Scheme 52)
Check for water contaminated fuel. Check EGR operation. Be sure valve seats properly and is not staying open. Check ignition system, particularly the distributor. If problem exists in cold weather, check cold start valve operation.
Check condition of spark plugs. If engine starts and immediately stalls, open distributor by-pass line. If engine then starts and runs okay, replace pick-up coil. If engine starts then stalls disconnect MAF sensor. If engine then runs and sensor connections are okay, replace MAF sensor (if equipped).

All Exc. 3.0L & 3.8L

Check fuel pressure. See FUEL SYSTEM DIAGNOSIS chart. (Scheme 52) Check for water contaminated fuel. Check TPS for sticking or binding. Check vacuum hose to MAP sensor for cuts or restrictions. Check alternator output voltage. If less than 9 or more than 16 volts, repair.
Check canister purge system for proper operation. Check ignition timing. Check spark plugs for fouling. Check PROM identification for proper application. Check HEI ground circuit 453 for good connection. Perform injector balance test. See INJECTOR BALANCE TEST chart. (Scheme 60)

3.0L & 3.8L

Check for proper seal of oil filler cap and tube. Check fuel pressure. See FUEL SYSTEM DIAGNOSIS chart. (Scheme 52) Check for water contaminated fuel. Check for air leaks at air duct between MAF sensor and throttle body.
Check TPS for sticking or binding. Check alternator output voltage. If less than 9 or more than 16 volts, repair. Check canister purge system for proper operation. Check the EGR system for valve sticking intermittently.

ROUGH, UNSTABLE IDLE

Check throttle linkage for sticking. Check idle speed. Check IAC system. See IDLE AIR CONTROL TEST chart. (Scheme 58) Check alternator output voltage. Repair if less than 9 or more than 16 volts.
Check injector balance. See INJECTOR BALANCE TEST chart. (Scheme 60) Check EGR system. There should be no EGR at idle. Check fuel pressure regulator operation. See appropriate article in COMPUTERIZED ENGINE CONTROLS. Check ignition system.
Disconnect MAF sensor. If condition persists, replace sensor. Check park or neutral and power steering pressure switches for proper operation. 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 TEST chart. Check for restricted fuel filter and water in tank. Check for low fuel pressure. See FUEL SYSTEM DIAGNOSIS chart.