Fuel Injection System - 2.0l Pfi Buick Skylark VI

DESCRIPTION

The Port Fuel Injection (PFI) system is controlled by the Electronic Control Module (ECM). The ECM monitors engine operation and environmental conditions. In addition to other functions, ECM output signals provide correctional adjustments for the air/fuel mixture and the idle speed.

Standard PFI systems feature simultaneous double-fire injection. Fuel injectors are pulsed once for each engine revolution, each spray providing 1/2 the fuel required for the combustion process.

In all systems, constant fuel pressure is maintained to the injectors. Air/fuel mixture is regulated by the time that injector stays open (pulse width). Various sensors provide information to the ECM to control pulse width. There are 2 major PFI sub-systems; fuel delivery system and electronic control system.

Note. Primary sub-systems affecting fuel system operation are covered in this article. Because of interrelated computer functions of system, refer to appropriate article in COMPUTERIZED ENGINE CONTROLS section in the ENGINE PERFORMANCE category for information on other ECM systems.

FUEL DELIVERY SYSTEM

The fuel system provides a constant, pressurized supply of fuel to the injectors. Fuel system consists of fuel tank, in-tank electric fuel pump, fuel pump relay, in-line fuel filter, fuel pressure regulator and fuel rail.

ELECTRONIC CONTROL SYSTEM

Electronic control system monitors engine operating conditions, processes the information, and controls engine for optimum performance and minimum emissions. Input signals are generated by the Coolant Temperature Sensor (CTS), Mass Airflow (MAF) sensor, exhaust Oxygen (O2) sensor, Throttle Position Sensor (TPS), Power Steering Pressure Switch (PSPS), Park/Neutral switch, Vehicle Speed Sensor (VSS), Manifold Air Temperature (MAT) sensor and Manifold Absolute Pressure (MAP) sensor.

Some engines may use a combination of MAT and MAP sensors in place of MAF sensor. The MAT and MAP sensors are used to determine airflow. The ECM may also receive signals from starter solenoid during cranking mode, air conditioning selector switch and distributor.

Fuel delivery system utilizes an in-tank electric fuel pump. Pump is integral with gauge sending unit. Fuel is pumped to the fuel rail through an in-line fuel filter. Fuel pump provides fuel at a pressure and volume exceeding engine requirements. Pressure regulator, mounted on the fuel rail, maintains a proper constant fuel pressure to the injectors. Pressure regulator increases the fuel pressure when engine vacuum decreases. Excess fuel is returned to the fuel tank through pressure regulator, using a fuel return line.

Scheme 169

FUEL PUMP

Fuel is supplied by 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. (Scheme 170) Once removed from tank, pump and sending unit are serviced separately. The pressure relief valve in the fuel pump, controls fuel pump maximum fuel pump pressure at 34-36 psi (4.2-6.3 kg/cm 2 ). Excess fuel flows through pressure regulator and returns to the tank.

The constant flow of cool fuel prevents fuel vapor bubbles. When ignition is turned on, fuel pump relay activates the fuel pump for 2 seconds to prime the injectors. If engine RPM signal is not received by the ECM during this time, the ECM deactivates fuel pump relay until engine starts. After engine starts, the ECM closes the fuel pump relay, activating the fuel pump.

As a back-up system to fuel pump relay, fuel pump can also be activated by the oil pressure switch. The oil pressure switch is normally open until oil pressure reaches approximately 4 psi (.28 kg/cm 2 ). If fuel pump relay fails, the oil pressure switch closes when oil pressure is obtained, operating the fuel pump. An inoperative fuel pump relay may result in extended cranking times due to the time required to build up oil pressure.

Scheme 170

FUEL PRESSURE REGULATOR

Fuel pressure regulator is a diaphragm-operated relief valve with injector pressure on one side and manifold pressure on the other. Pressure regulator compensates for engine load by increasing fuel pressure when low manifold vacuum is experienced.

During periods of high manifold vacuum, regulator return orifice is fully open, keeping fuel pressured on the low side of its regulated range. As throttle valve opens, vacuum to regulator diaphragm decreases, allowing spring tension to gradually close off return passage. At wide open throttle when vacuum is at its lowest, return orifice is restricted, providing maximum fuel volume and maintaining constant fuel pressure to injectors. (Scheme 171)

Scheme 171

FUEL RAILS

Fuel rail assembly includes a fuel pressure regulator and individual high pressure fuel injectors. The fuel injectors fit into individual sockets of base plate. Injectors are force fit into fuel rail opening. Retainer clip is pushed into its locked position. Some retainer clips must be rotated in the proper direction to lock. The fuel rail provides the upper mount for fuel injectors. Spring-loaded pressure tap may be used for testing fuel system.

FUEL INJECTORS

The port fuel injector solenoid is controlled by the ECM. The injector consists of a valve body with a specially ground needle valve. The moveable armature is attached to the needle valve. Needle valve is held against nozzle sealing seat by spring pressure.

Each injector utilizes a double-wire connector. One wire supplies voltage when ignition is on. Second wire connects to the internally regulated ECM ground and controls injector pulse width. Electric pulses (generated by the ECM) produce a magnetic field in injector solenoid winding. This draws the armature back against spring pressure and lifts needle from the seat, allowing pressurized fuel to be injected. When injector is de-energized, spring pressure forces the needle valve closed. (Scheme 172)

Fuel injector is installed in intake mainfold at each cylinder. Injector sealing is provided by "O" rings. Lower "O" ring seals between injector and intake manifold. Upper "O" ring seals between injector and fuel rail. Always replace "O" rings when injector is removed.

Scheme 172

Note. On Sequential Fuel Injection (SFI), wiring harness MUST be connected to the correct injector. The ECM ground circuit for each injector is color coded differently for identification.

AIR INDUCTION SYSTEM

Air is drawn into the induction system through an air pick-up duct. This ensures intake air temperature is lower than engine compartment temperatures, resulting in denser air supply to combustion chambers. Air intake duct provides turbulance free airflow for accurate measurement at the MAF sensor. Rubber boot between MAF sensor and throttle body prevents this air leakage. Duct between MAF and throttle body must be air tight. Air entering behind the MAF sensor will not be measured, causing a lean air/fuel mixture.

THROTTLE BODY

The throttle body controls the amount of air entering the intake manifold. Mounted on the throttle body are the TPS and IAC valves. The TPS enables ECM to determine throttle position under all operating conditions. Throttle body contains vacuum ports used to supply signals to various components. On some models, engine coolant is routed through bottom of throttle body to warm housing and prevent icing. (Scheme 173)

Scheme 173

IDLE AIR CONTROL

The Idle Air Control (IAC) valve controls engine idle speed during engine load changes to prevent stalling. Mounted in the throttle body, the IAC controls air by-passed around throttle valve. Movement of IAC conical valve inward toward the seat decreases airflow while movement away from the seat increases airflow around throttle plate. The IAC valve moves in small steps called "counts", and can be measured with a "Scan" tester plugged into the Assembly Line Diagnostic Link (ALDL). Increase of counts indicates more air passing IAC valve.

Proper positioning of IAC valve at idle is determined by the ECM based on battery voltage, coolant temperature, engine load and engine RPM. When engine speed drops to less than desired RPM (with throttle plate closed), the ECM senses a near stall condition. The ECM then repositions IAC valve to prevent stalling.

Disconnecting and reconnecting of IAC valve with engine running will result in incorrect idle RPM. The IAC valve must be reset, vehicle is reset when vehicle is operated over 35 MPH. When servicing IAC, disconnect or connect only with ignition off to prevent required resetting of IAC.

The IAC valve affects only the idle system. If valve is stuck fully open, excessive airflow into the manifold creates a high idle speed. Valves stuck closed allows insufficient airflow, resulting in low idle speed. For calibration purposes, several different design IAC valves are used. Make sure the proper design of valve is used during replacement.

Speed Density

On models equipped with MAP and MAT sensors, the speed density is used to compute the airflow rate. Manifold pressure and temperature are used to calculate the airflow rate to the ECM. The MAP sensor responds to manifold vacuum changes due to engine load and speed changes.

The ECM sends a volt signal to the MAP sensor. Manifold pressure changes result in resistance changes of MAP sensor. By monitoring MAP sensor output voltage, the ECM determines manifold pressure. If MAP sensor fails, the ECM will apply a fixed MAP value and use the TPS to control fuel.

Mass Airflow

Air mass entering the induction system is measured by the MAF sensor. A ceramic resistor is used to measure incoming air temperature. Incoming air cools the sensing element. Measurement of electrical power to maintain the MAF sensor ceramic resistor at 165°F (75°C) greater than the incoming air temperature determines the air mass. (Scheme 174) The electrical power requirement is measured and converted to a digital signal (30-150 Hz), which is then sent to the ECM. This is then used to determine engine load.

Using calculations of mass airflow, engine temperature and RPM, the ECM calculates the fuel requirement to provide a proper air/fuel ratio of as close to 14.7:1 as possible.

Some MAF units are the Bosch hot wire type. This type contains a sensing wire. Current is supplied to maintain a calibrated temperature. Current varies with amount of airflow. Current changes are processed by the ECM to provide proper air/fuel ratio.

Sensing wire contamination is prevented by heating sensing wire to 1000°F (538°C) after engine shutdown. This burn off cycle is controlled by the ECM. If burn off cycle did not occur, the "SERVICE ENGINE SOON" light will activate and stay on after next engine start. A Code 36 will be stored in memory.

Scheme 174

PRELIMINARY CHECKS

Note. For diagnostic flow charts mentioned in PRELIMINARY CHECKS, see appropriate article in COMPUTERIZED ENGINE CONTROLS section in the ENGINE PERFORMANCE category.

Subsystem Checks

Before using procedures in this TROUBLE SHOOTING section, perform DIAGNOSTIC CIRCUIT CHECK to determine that ECM and "SERVICE ENGINE SOON" light are working properly. See appropriate TESTS W/CODES article in the COMPUTERIZED ENGINE CONTROLS section in the ENGINE PERFORMANCE category for the associated DIAGNOSTIC CIRCUIT CHECK . This also determines that there are no stored trouble codes, or that there is trouble code but no "SERVICE ENGINE SOON" light. If "engine cranks but will not run", see appropriate CHART A-3 in COMPUTERIZED ENGINE CONTROLS section in the ENGINE PERFORMANCE category.

The following should be checked prior to trouble shooting fuel system

1. ECM grounds are clean and tight.
2. Check for faulty vacuum hoses.
3. Check for vacuum leaks at throttle body and intake manifold.
4. Check ignition system for faulty components.
5. Inspect wiring connections and condition.

FUEL PRESSURE RELIEF

1. Fuel system is under pressure. Pressure must be relieved prior to servicing fuel system. Fuel pressure may be relieved by 2 different methods.
2. One method is to disconnect fuel pump at rear body connector. Start engine and allow to run until it stops. Operate starter for 3 seconds to remove remaining fuel from fuel lines. Reconnect fuel pump once repair is completed.
3. The other method is to install Fuel Pressure Gauge (J-34730-1) on fuel pressure connection. Wrap shop towel around pressure connection when installing fuel pressure gauge to absorb fuel leakage.
4. Install gauge bleed hose in container. Open bleed valve to bleed fuel pressure.

FUEL SYSTEM DIAGNOSIS

Note. For specific fuel pressure testing procedures see appropriate CHART A-7, FUEL SYSTEM DIAGNOSIS. For additional testing and diagnosis information, see TROUBLE SHOOTING in CCC THEORY & OPERATION article in COMPUTERIZED ENGINE CONTROLS section in the ENGINE PERFORMANCE category.

REMOVAL & INSTALLATION

Removal

1. Relieve fuel pressure. See «FUEL PRESSURE RELIEF»(/buick/skylark/vi-1986-1992/remont/testing-diagnostics/#fuel-injection-system-20l-pfi__fuel-pressure-relief) under TESTING & DIAGNOSIS in this article. Turn ignition off. Disconnect wiring connectors from injectors. Disconnect and plug hoses to fuel rail.
2. Remove fuel rail retaining bolts. Remove injector-to-fuel rail retaining clip (if used). Separate fuel rail from injectors. Remove injectors. (Scheme 175)

Scheme 175

Note. If injector is replaced, ensure replacement injector is the same part number as that removed.

Installation

Coat new "O" rings with oil. Install "O" rings on injectors. Reverse removal procedure. Tighten fuel rail retaining bolts to specification. See TORQUE SPECIFICATIONS table.

IDLE AIR CONTROL VALVE

Remove electrical connector from IAC valve. Remove IAC valve and gasket or "O" ring. IAC valve screws into housing on 2.0L vehicles.

1. The extended distance of a new IAC must be checked prior to installation. Damage will occur if measurement is incorrect. Distance must not exceed 1 1/8" (28 mm). Measurement should be taken from valve housing flange to end of cone. DO NOT extend or retract pintle on IAC valve which has been in service or damage to internal worm drive may occur.
2. To retract pintle on new IAC, slowly exert finger pressure on valve. Identify IAC valve as being either a type I or type II valve. Type I IAC valve has a collar around the connector end of IAC valve. (Scheme 176)
3. To retract type I IAC valve, exert firm pressure on plunger (a slight side-to-side movement may be helpful). To retract plunger on type II IAC valve, compress retaining spring from valve while turning valve inward with a clockwise motion. Return spring to original position with straight portion of spring end aligned with flat surface of valve.
4. Install new "O" ring or gasket on valve. Coat "O" ring with oil. Install IAC valve. Tighten IAC valve to 13 ft. lbs. (18 N.m).
5. Install electrical connector. The IAC resets when ignition switch is turned from the "ON" to the "OFF" position (at speeds greater than 35 MPH on 2.0L). On some models it may be necessary to shift transmission into Drive (auto. trans.) or Neutral (man. trans.) before learning process is complete.

Scheme 176

OXYGEN SENSOR

Disconnect negative battery cable. Disconnect electrical lead from O2 sensor. Sensor may be difficult to remove when engine temperature is less than 120°F (48°C). Remove O2 sensor.

1. Coat O2 sensor threads with Anti-Seize Compound (5613695) prior to installation. New sensors already contain anti-seize compound.
2. Install sensor and tighten to 30 ft. lbs. (41 N.m). Install electrical connector.

Disconnect electrical connection from TPS. Remove TPS retaining screws. Remove TPS.

1. With throttle valve in closed position, install TPS on throttle body. Ensure TPS lever engages with drive lever on throttle shaft. Install retaining screws and electrical connection.
2. The TPS on most models are self-zeroing and are not adjustable. On these models, as long as voltage is within a certain range, or less than 1.25 volts, TPS need not be serviced. On adjustable models, adjust TPS to specification and tighten retaining screws. See THROTTLE POSITION SENSOR in appropriate TUNE-UP article in TUNE-UP section in the ENGINE PERFORMANCE category.

1. Remove air inlet ducts. Disconnect and mark electrical connections and vacuum hoses from throttle body. Disconnect control cables from throttle body.
2. Drain cooling system. Remove coolant hoses. Remove throttle body retaining bolts. Remove throttle body and gasket.

Note. Identification number is stamped on throttle body near coolant cover. Identification number must be used for ordering replacement components.

1. Reverse removal procedure using new gasket. Tighten retaining bolts to specification. See «TORQUE SPECIFICATIONS»(/buick/skylark/vi-1986-1992/remont/testing-diagnostics/#fuel-injection-system-20l-pfi__torque-specifications) table. Fill cooling system.
2. If a new IAC is being installed, ensure proper length setting prior to installation. See «IDLE AIR CONTROL VALVE»(/buick/skylark/vi-1986-1992/remont/testing-diagnostics/#fuel-injection-system-20l-pfi__idle-air-control-valve) under REMOVAL & INSTALLATION in this article. Adjust idle speed and TPS (if removed). See appropriate article in TUNE-UP section.

1. Relieve fuel pressure. See «FUEL PRESSURE RELIEF»(/buick/skylark/vi-1986-1992/remont/testing-diagnostics/#fuel-injection-system-20l-pfi__fuel-pressure-relief) in this article. Disconnect the pressure regulator-to-fuel rail hose. Refer to «FUEL RAIL & INJECTORS»(/buick/skylark/vi-1986-1992/remont/testing-diagnostics/#fuel-injection-system-20l-pfi) under REMOVAL & INSTALLATION in this article.
2. Remove pressure regulator retaining bolts. Remove pressure regulator from fuel rail.

Lubricate fuel rail seal with oil and install in regulator. On all models, reverse removal procedure. Tighten bolts to specification. See TORQUE SPECIFICATIONS table.

1. Disconnect negative battery cable. Relieve fuel pressure. See «FUEL PRESSURE RELIEF»(/buick/skylark/vi-1986-1992/remont/testing-diagnostics/#fuel-injection-system-20l-pfi__fuel-pressure-relief) in this article. Remove filler neck. Lower fuel tank. Disconnect fuel lines and electrical connection.
2. Remove fuel level sending unit and pump retaining bolts or cam lock ring. Lift assembly from fuel tank and remove fuel pump from sending unit.
3. Pull fuel pump upward while pulling outward away from bottom support. Use care not to damage rubber insulator and strainer. Reverse removal procedure for installation using new "O" ring gasket.

ADJUSTMENTS

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

TORQUE SPECIFICATIONS

TORQUE SPECIFICATIONS

See also:
• FUEL PRESSURE RELIEF
• TORQUE SPECIFICATIONS
• IDLE AIR CONTROL VALVE
• FUEL RAIL & INJECTORS