Fuel Injection System - Pfi Buick Electra VI

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, or Electronic Control Module (ECM). The ECM is the heart of the system and reads output signals from sensors to determine proper air/fuel ratio, ignition timing and idle speed. The ECM also has the ability to perform some diagnostic work on itself and the system.

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 a charge for each combustion cycle. On Century, Ciera, Delta 88, Electra, Ninety-Eight, Regal, Regency and Toronado models, the injectors are pulsed sequentially (one-by-one) in spark plug firing order. There is one injection of fuel for every combustion cycle. This system is referred to as Sequential Fuel Injection (SFI). Camaro, Corvette and Firebird PFI systems are referred to as Tuned Port Injection (TPI).

All 3 systems maintain constant fuel pressure to the injectors. Therefore, the air/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 the 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 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. The electronic control system then processes these conditions, and controls the engine for optimum performance and minimum emissions.

Input signals are generated by the Engine Coolant Temperature (ECT) sensor, Mass Airflow (MAF) sensor, Oxygen (O2) sensor, Throttle Position Sensor (TPS), Park/Neutral switch, Vehicle Speed Sensor (VSS), Manifold Air Temperature (MAT) sensor and Manifold Absolute Pressure (MAP) sensor.

Some 2.8L engines may use a combination of the MAF, MAT and MAP sensors. On 2.0L Turbo engines the MAP and MAT sensors are used to determine airflow. The ECM also receives signals from the starter solenoid, air conditioning selector switch and 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 indicates to the ECM the oxygen content of exhaust gases. The ECM then adjusts the air/fuel ratio to the engine by controlling injector on time.

The fuel control system consists of the following components: 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 fuel tank. An electric fuel pump, located in fuel tank with 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.

The pressure regulator, located on the fuel rail, regulates fuel pressure to injectors. Excess fuel is returned to the fuel tank by a separate return line. In order for fuel injectors to supply a precise amount of fuel at the command of the ECM, the fuel system maintains a constant pressure of approximately 34-46 psi (2.4-3.2 kg/cm 2 ) at injectors. The pressure regulator compensates for engine load by increasing fuel pressure as manifold pressure drops.

When the ignition is turned on, ECM will turn on the in-tank fuel pump. It will remain on as long as the engine is cranking or running. ECM uses distributor reference pulses to determine when engine is running. The ECM also uses the oil pressure switch as a back-up system to determine when engine is running.

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 fuel gauge sending unit. Once removed from tank, the pump and sending unit are serviced separately.

Fuel pressure is achieved by rotation of armature driving the roller vane components. The impeller at 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 maintain fuel pump pressure at 60-90 psi (4.2-6.3 kg/cm 2 ). The fuel pump delivers more fuel than the engine can consume even under the most extreme conditions. Excess fuel flows through pressure regulator and back to fuel tank through return line.

The constant flow of fuel allows fuel system to always be supplied with cool fuel, thereby preventing the formation of fuel vapor bubbles. When the ignition is first turned on without engine running, the ECM will turn on fuel pump relay for 2 seconds. This will rapidly pressurize fuel system. If the engine is not started within 2 seconds, the ECM will shut fuel pump off and wait until engine starts.

2.8L Port Fuel Injection System Diagram This diagram is a basic representation of all GM PFI systems. Scheme 1

As soon as engine is cranked, the ECM will turn on relay and run the fuel pump. As a back-up system to 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 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 engine is cold. (Scheme 2)

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 constant fuel pressure at injectors at all times. The pressure regulator also compensates for engine load by increasing fuel pressure when low manifold vacuum is experienced.

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 3)

FUEL RAILS

The extruded fuel rail assembly includes a fuel pressure regulator, individual high pressure fuel injectors and cold start injector. The injectors fit into individual sockets in the base plate. The fuel rails used on 2.0L, 3.0L and 3.8L engines are manufactured, assembled and flow tested with the injectors as an assembly.

Scheme 2

Scheme 3

Scheme 4

The injectors are force fitted into the opening on the fuel rail. (Scheme 4) The injectors are locked in place with the aid of an injector retainer clip which must be rotated in the proper direction.

FUEL INJECTORS

The port fuel injector is a solenoid operated device controlled by the ECM. The ECM energizes solenoid, which in turn opens the valve allowing pressurized fuel to be injected just ahead of intake valve. ECM achieves its predetermined air/fuel ratio by energizing the injector for a specific amount of time.

As the injector is energized a needle valve is opened allowing pressurized fuel to flow past valve and through nozzle. As pressurized fuel flows past nozzle a conical spray pattern is produced. Excess fuel then passes through regulator before returning to tank.

Each injector has 2 "O" rings. The lower "O" ring provides a seal between the injector and intake manifold. The upper "O" ring provides a seal between the injector and fuel rail. Vacuum leakage at the injector intake area will create a lean cylinder or driveability problem.

Each injector has a 2-wire connector. One wire supplies voltage from the fuse(s) in the fuse panel. The second wire connects to ECM, which controls the ground to operate the injector 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.

Scheme 5

Note. Because of sequential pulsing of the injectors in SFI systems, the wiring harness must be connected to the proper injector or a lean cylinder and driveability problem will occur. See WIRING DIAGRAMS in this article for proper connections.

COLD START VALVE

The cold start valve is used to provide additional fuel during the crank mode to improve cold engine starting. This circuit is important when engine coolant temperature is low. The main injectors are not pulsed long enough to provide adequate fuel needed to start a 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 coolant temperature is below 68°F (20°C), the switch is closed, feeding power to the cold start injector. However, cold start valve is still 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 simultaneously heated the switch enough for it to open within the prescribed time period. In either situation the switch will in no way actuate the cold start injector for longer than an 8 second period.

AIR INDUCTION SYSTEM

Air is drawn into the induction system through an air pick-up duct mounted in front of the radiator support. This arrangement ensures that air entering port injection system, is outside the high temperatures of the engine compartment. The result is cooler, denser air charges to the combustion chambers. The smooth contour of the air duct system is essential and provides a turbulence free airflow into the MAF sensor to ensure accurate air measurements.

Since the amount of air entering the induction system is measured by the MAF sensor only, any air that enters 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 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 has a throttle valve to control the amount of air delivered to the engine. Mounted on the throttle body are the TPS and IAC valves. The throttle body also contains vacuum ports located at, above or below the throttle valve. These ports provide the necessary vacuum signals needed by various components. To prevent icing, engine coolant is directed through the bottom of the throttle body. (Scheme 6)

Exploded View of Typical Throttle Body All models have similar parts in different configurations. Courtesy of General Motors Corp. Scheme 6

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 engine 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 (2.0L Turbo & Fiero 2.8L Only)

The speed density technique of computing airflow rate is used on Skyhawk and Sunbird 2.0L 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.

Mass Airflow

Mass airflow is determined 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, an air temperature sensing 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/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 7)

Scheme 7

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. It is considered normal for idle speeds to vary. On 2.0L and Fiero 2.8L engines minimum idle speed is not adjustable.

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

1. With IAC motor connected, ground diagnostic test lead. Turn ignition on, but do not start engine. Wait at least 30 seconds.
2. With ignition on, disconnect IAC electrical connector. Remove ground from diagnostic lead and start engine. Pierce idle stop screw plug with an awl, and remove plug.
3. Adjust minimum idle speed screw to obtain an idle speed of 550 RPM on models equipped with 2.8L automatic transmission (in Drive) and 650 RPM on models equipped with 2.8L manual transmission. Adjust to 450-550 RPM (in Drive) on all 3.0 and 3.8L vehicles. (Scheme 6)

Note. On 5.0L and 5.7L engines, the distributor set timing connector should be unplugged before the following procedure is attempted. (Scheme 8)

5.0L & 5.7L

1. Pierce idle stop screw plug with an awl, and remove plug. With IAC motor connected, ground diagnostic lead.
2. Turn ignition on, but do not start engine. Wait at least 30 seconds. Disconnect IAC electrical connector. Disconnect distributor Set-Timing connector. Start engine and allow to go to closed loop.
3. 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.

Note. Anytime minimum idle speed adjustment has taken place (on all models) the Throttle Position Sensor (TPS) must be readjusted to factory specification.

Scheme 8

THROTTLE POSITION SENSOR (TPS) ADJUSTMENT

Note. Throttle position sensor on 2.0L and 2.8L Fiero models are not adjustable.

2.8L, 3.0L, 5.0L & 5.7L

1. Install "Scan" tool and select TPS. With ignition switch in "ON" position, adjust TPS to specification. See «TPS SPECIFICATIONS»(/buick/electra/vi-1985-1990/remont/testing-diagnostics/#fuel-injection-system-pfi) for voltage adjustment. Adjust TPS output voltage in closed throttle position.
2. On all models except 2.8L and 3.0L engines, remove 2 TPS hold-down screws and apply Loctite (262) to threads and reinstall. Tighten screws and recheck voltage readings.

TPS SPECIFICATIONS

3.8L

1. Install 3 jumper wires between TPS and harness connector. With ignition on, connect a digital voltmeter to "B" and "C" terminals of the TPS connector. (Scheme 9)
2. Adjust TPS in the closed throttle position to obtain specified output voltage. Tighten screws and recheck adjustment.

Scheme 9

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. On 2.8L (VIN W) remove IAC attaching screws.

Scheme 10

1. Before installing new IAC valve, measure the distance that valve is extended. (Scheme 10) 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 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 10)
3. To retract Type I, exert firm pressure on valve. To retract Type II, compress retaining spring while turning valve in with a clockwise rotation. Return spring to original position.
4. Either valve should be installed with a new gasket. Tighten to 13 ft. lbs. (18 N.m). On 2.8L (VIN W) install valve using new "O" ring. Lubricate "O" ring with engine oil before installation. Tighten attaching screws to 30 INCH lbs. (3.4 N.m).
5. Install electrical connector on valve. Start engine. ECM will reset idle speed when vehicle is driven above 35 MPH, or when engine is started and ignition is turned off.

Note. When replacing IAC valve or any other sensor, it is important to check that correct replacement part number is used.

1. Disconnect negative battery cable. On some 2.8L engines, vehicle should be safely raised on hoist because sensor is mounted behind exhaust "Y" pipe.
2. Unplug O2 sensor electrical connector. O2 sensor may be difficult to remove when engine temperature is below 120°F (48°C). Remove O2 sensor.

1. Oxygen sensor threads must be coated with 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 (5613695). Tighten sensor 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 2.0L models and 2.8L Fiero models, tighten screws and install connector. On all other models, TPS must be adjusted before tightening screws. See «THROTTLE POSITION SENSOR (TPS) ADJUSTMENT»(/buick/electra/vi-1985-1990/remont/testing-diagnostics/#fuel-injection-system-pfi__throttle-position-sensor-tps-adjustment) in this article.

Removal & Installation (Except Corvette)

1. 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 from fuel tank and remove fuel pump from sending unit.
2. Pull fuel pump up while pulling outward away from bottom support. Make sure not to damage rubber insulator and strainer. To install, reverse removal procedure. Use new "O" ring gasket.

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.

TROUBLE SHOOTING

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 sensor reading is not what it should be, as compared to what is in ECM memory, ECM will turn on the "CHECK ENGINE" or "SERVICE ENGINE SOON" light on instrument panel, and will store a trouble code in memory.

Scheme 11

1. To obtain a stored trouble code from ECM, the Assembly Line Communication Link (ALCL) is used. The ALCL connector is located in passenger compartment. To enter diagnostic mode, connect diagnostic terminal (terminal "B") to ground (terminal "A") with engine off. (Scheme 11)
2. The ECM will first display a code 12, to indicate 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.
3. 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 diagnostic terminal ground is removed.

TROUBLE CODES

The following codes indicate these problems.

Code 13

Oxygen sensor circuit open.

Code 14

Coolant sensor reading too high.

Code 15

Coolant sensor reading too low.

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. MAP sensor signal voltage high on 2.0L Turbo.

Code 34

MAF sensor signal voltage too low. MAP sensor signal voltage low on 2.0L Turbo.

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.

Code 61

ECM has read slow or sluggish voltage change time, indicating that O2 sensor is contaminated or degraded.

Code 63

Manifold absolute pressure sensor reads low vacuum.

Code 64

Manifold absolute pressure sensor reads high vacuum.

CLEARING TROUBLE CODES

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

Turn ignition switch to "ON" position 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

Note. For diagnostic flow charts see appropriate article in COMPUTER CONTROLS section.

Prior to diagnosing 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. Cylinder 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 PRESSURE DIAGNOSIS

This information is not contained here. See chart A7 found in the trouble chart section of the ENGINE PERFORMANCE section.

HARD START

Note. If engine starts but dies immediately, see ENGINE CRANKS BUT WON'T RUN diagnostic chart in appropriate COMPUTER ENGINE CONTROL (CEC) article in COMPUTER CONTROLS section.

1. Check fuel pump relay by probing fuel pump test terminal with a test light to ground. Turn ignition off for 10 seconds, and then turn ignition on. Test lamp should light for 2 seconds. If test light 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. See the FUEL SYSTEM DIAGNOSIS chart in the appropriate PFI TESTS W/ CODES in COMPUTERIZED ENGINE CONTROL section.
3. 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.
4. 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 and then stalls, disconnect MAF sensor. If engine then runs and sensor connections are okay, replace MAF sensor (if equipped)

All Engines Except 3.0L & 3.8L

1. Check fuel pressure. See FUEL SYSTEM DIAGNOSIS chart in the appropriate PFI TESTS W/ CODES. 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. Voltage should range from 9-16 volts. If voltage is outside range, repair as necessary.
2. 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»(/buick/electra/vi-1985-1990/remont/testing-diagnostics/#fuel-injection-system-pfi) chart following TROUBLE SHOOTING section.

3.0L & 3.8L

1. Check for proper seal of oil filler cap and tube. Check fuel pressure. See FUEL SYSTEM DIAGNOSIS chart in the appropriate PFI TESTS W/ CODES. 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. Voltage should range from 9-16 volts. If voltage is outside range, repair as necessary. 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 in the appropriate PFI TESTS W/ CODES article. Check alternator output voltage. Voltage should range from 9-16 volts. If voltage is outside range, repair as necessary.
2. Check injector balance. See «INJECTOR BALANCE TEST»(/buick/electra/vi-1985-1990/remont/testing-diagnostics/#fuel-injection-system-pfi) chart. Check EGR system. There should be no EGR at idle. Check fuel pressure regulator operation. See FUEL SYSTEM DIAGNOSIS in the appropriate PFI TESTS W/ CODES article. Check ignition system.
3. 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 in the appropriate PFI TESTS W/ CODES.

DETONATION

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

Scheme 12

Wiring Diagram: 2.0L Turbo Port Fuel Injection System. Scheme 13

Wiring Diagram: Beretta & Corsica 2.8L PFI System. Scheme 14

Wiring Diagram: Camaro & Firebird 2.8L PFI System. Scheme 15

Wiring Diagram: Cavalier & Firenza 2.8L PFI System. Scheme 16

Wiring Diagram: Century, Celebrity, Ciera & 6000 2.8L PFI System. Scheme 17

Wiring Diagram: Fiero 2.8L Port Fuel Injection System. Scheme 18

Wiring Diagram: Calais, Grand Am, Skylark & Somerset 3.0L PFI System. Scheme 19

Wiring Diagram: Bonneville, Electra, LeSabre, Delta 88 & Ninety Eight 3.8L PFI System. Scheme 20

Wiring Diagram: Century & Ciera 3.8L PFI System. Scheme 21

Wiring Diagram: Regal 3.8L Turbo PFI System. Scheme 22

Wiring Diagram: Riviera 3.8L PFI System. Scheme 23

Wiring Diagram: Toronado 3.8L PFI System. Scheme 24

Wiring Diagram: Camaro & Firebird 5.0L & 5.7L PFI System. Scheme 25

Wiring Diagram: Corvette 5.7L Port Fuel Injection System. Scheme 26

See also:
• TPS SPECIFICATIONS
• THROTTLE POSITION SENSOR (TPS) ADJUSTMENT