Fuel Injection System - 2.0l/2.5l Tbi Chevrolet Corsica I

COMPONENT TESTING

Note. See TROUBLE SHOOTING .

IDENTIFICATION

An 8-digit unit identification number is stamped on throttle body assembly. On model 700, number can be found on TPS side of mounting flange. Letter codes are stamped on throttle body at external tube locations to identify vacuum hose connections.

DESCRIPTION

TBI system has 2 major sub-systems: electro-mechanical fuel delivery system and electronic air/fuel control system. Fuel delivery system includes electric fuel pump and fuel pump relay. Air/fuel control system includes Electronic Control Module (ECM), Throttle Body Injector (TBI) assembly, Idle Air Control (IAC) System and data sensors. ECM uses information received from sensors to control air/fuel ratio, ignition timing and emission devices.

Fuel Pump

An electric fuel pump (located inside fuel tank as integral part of fuel gauge sending unit) delivers fuel under pressure to throttle body assembly. Fuel pump relay controls fuel pump operation. When ignition switch is turned to "ON" position, fuel pump relay activates fuel pump for 2 seconds to prime injector. If ECM does not receive reference pulses from ignition module (engine cranking) after this period, ECM deactivates fuel pump relay. Fuel pump relay will be activated again when ECM receives distributor reference pulses.

As back-up system to fuel pump relay, fuel pump can also be turned on by oil pressure sender. Oil pressure sender has 2 internal circuits. One circuit operates oil pressure indicator in instrument panel. Second circuit is a normally open switch which closes when oil pressure reaches about 4 psi (.3 kg/cm 2 ). If fuel pump relay fails, oil pressure sender will close and run fuel pump.

Throttle Body Injection (TBI) Assembly

TBI assembly consists of 2 castings, throttle body and fuel meter assembly. Throttle body has throttle valve, Idle Air Control (IAC), and Throttle Position Sensor (TPS). The fuel meter body has fuel meter assembly, pressure regulator and injector. Throttle body casting may contain ports to supply vacuum signals for EGR valve, MAP sensor and canister purge system.

Fuel Injector(s)

Fuel injector is a solenoid controlled by ECM. Fuel is supplied at lower end of injector by fuel delivery system. Pressure to injector is maintained at 9-13 psi (.6-.9 kg/cm 2 ) by the pressure regulator. Excess fuel passes through pressure regulator and is returned to fuel tank. Battery voltage is supplied to the injector when the ignition is on. ECM energizes solenoid by providing a ground path through its internal circuitry. This creates a magnetic field in the injector windings, causing the normally closed ball valve to lift off its seat. Fuel under pressure is injected in a conical spray pattern at walls of throttle bore, above throttle valve.

During engine cranking, fuel injector is pulsed (activated) once for each ignition reference pulse received by ECM. This is referred to as synchronized mode. In non-synchronized mode, injector is pulsed once every 6.25-12.5 milliseconds, depending upon engine calibration and operating conditions. In this mode, pulse is totally independent of distributor reference pulses.

On the 5.0L and 5.7L model 220 TBI units, 2 injectors are used in the throttle body. Injectors are alternately sprayed, using ignition module reference pulses.

Scheme 9

IDLE AIR CONTROL (IAC) SYSTEM

IAC system consists of electrically controlled motor (actuator) which positions a pintle in the air by-pass channel around throttle valve. (Scheme 9) IAC is held in by screws on the model 700 TBI. ECM calculates desired position of IAC valve based upon battery voltage, coolant temperature, engine load and engine speed, to control idle speed and prevent stalls due to engine load changes.

There are several different conical IAC pintle designs used. Ensure that correct design and type is used if IAC is replaced.

ELECTRONIC CONTROL MODULE (ECM)

The ECM not only controls fuel delivery but also performs diagnostic functions for the systems that affect vehicle performance. Information from all data sensors is received and processed by ECM to produce proper pulse duration ("on" time) for injector. For additional information on sensors and ECM controls, refer to CCC THEORY/OPERATION article. The ECM performs calculations to control fuel operating modes such as starting, clear flood, run, acceleration, deceleration, battery voltage correction and fuel cut-off. ECM's have "learning process" capacity.

PROM

To allow one model of ECM to be used in different vehicles, a Programmable Read Only Memory (PROM) is used. The PROM is a replaceable chip located inside the ECM and contains information pertaining to the vehicle's weight, engine, transmission, axle ratio and other powertrain related variables. The PROM is very specific and must be used with the correct vehicle. Some models may also contain a fuel back-up chip referred to as a CALPAC. If the ECM or the PROM were to fail, the CALPAC contains circuitry which would enable vehicle to be driven in for service.

Note. Always check with latest parts book and service bulletin information for the correct part number when replacing PROM or CALPAC.

Starting

During engine starts, ECM delivers injector pulse for each distributor reference pulse received (synchronized mode). Injector pulse width is based upon coolant temperature and throttle position. Air/fuel ratio is determined by ECM when throttle position is less than 80 percent open. Engine starting air/fuel ratio ranges from 1.5:1 at -33°F (-36°C) to 14.7:1 at 201°F (94°C). At lower coolant temperatures, injector pulse width is longer (richer air/fuel mixture ratio). When coolant temperature is high, injector pulse width becomes shorter (leaner air/fuel ratio).

Clear Flood

If engine is flooded, driver must depress accelerator pedal to Wide Open Throttle (WOT) position. At this position, ECM calculates injector pulse width equal to air/fuel ratio of 20:1. This air/fuel ratio will be maintained as long as throttle remains in wide open position and engine speed is less than 600 RPM. If throttle position becomes less than 80 percent open and/or engine speed exceeds 600 RPM, ECM changes injector pulse width to that used during engine starting (based upon coolant temperature and manifold vacuum).

Run

When engine speed is greater than 400 RPM, ECM operates in "open loop". In "open loop", ECM calculates injector pulse width based upon coolant temperature and Manifold Absolute Pressure (MAP). Engine will remain in "open loop" operation until O2 sensor reaches operating temperature, coolant temperature reaches preset temperature, and a specific period of time has elapsed after engine starts. When all these conditions are met, ECM operates in "closed loop". In "closed loop", ECM controls injector pulse width based upon O2 sensor signals (in addition to other input parameters) to maintain as close to a 14.7:1 air/fuel mixture as possible.

Acceleration

Fuel enrichment during acceleration is provided by ECM. Sudden opening of throttle valve causes rapid increase in MAP. Pulse width is directly related to MAP, throttle position and coolant temperature. Higher MAP and wider throttle angles give wider pulse width (richer mixture). During enrichment, injector pulses are not in proportion to distributor reference signals (non-synchronized). Any reduction in throttle angle cancels fuel enrichment.

Deceleration

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

Battery Voltage Correction

ECM compensates for low battery voltage by increasing injector pulse width and increasing idle RPM. ECM is able to perform these commands because of a built-in memory function.

Fuel Cut-Off

No fuel is delivered when ignition is turned off so that dieseling is prevented. No fuel is delivered if no reference pulses are sent by distributor even with ignition on. This prevents flooding before starting. Fuel cut-off will also occur at high engine RPM to prevent internal damage to engine.

Fuel Injector Resistance Specifications 2.0L

The 2.0L engine fuel injector resistance specification is over 1.6 ohms, but not open circuit.

DATA SENSORS

Note. For information on data sensors see CCC THEORY/OPERATION article in this section.

PRELIMINARY CHECKS

Note. For diagnostic flow charts mentioned in PRELIMINARY CHECKS, see 2.0L(K)/2.5L TESTS W/CODES article in this section.

Subsystem Checks

Before using trouble shooting section, perform DIAGNOSTIC CIRCUIT CHECK to determine that ECM and "SERVICE ENGINE SOON" light are working properly. This also determines that there are no stored trouble codes, or that there is trouble code but no "SERVICE ENGINE SOON" light.

Determine if fuel control system is operating properly by performing "Field Service Mode" check of DIAGNOSTIC CIRCUIT CHECK. Verify complaint. If "engine cranks but will not run", see CHART A-3 in 2.0L(K)/2.5L TESTS W/CODES article in this section.

Before testing fuel injection system for cause of malfunction, check that following subsystems and components are in good operating condition

1. Battery and charging system.
2. Engine state of tune.
3. Emission control devices.
4. Fuel system pressure and delivery volume.
5. Wiring connectors at components.
6. Vacuum hoses for splits, kinks and proper connections.
7. Air leaks at throttle body mounting and intake manifold.

FUEL PRESSURE

Note. See FUEL PRESSURE RELIEF & TEST under REMOVAL & INSTALLATION.

Fuel System Pressure Relief & Test (Skylark 2.5L. VINS A, U)

Note. The fuel pressure relief procedure in steps 1 & 2 is updated for Skylark courtesy of Buick dealer service bulletin 91-6C-1, March, 1991.

1. Loosen fuel filler cap to remove tank pressure. DO NOT tighten at this time. Raise vehicle. Disconnect fuel pump electrical connector. Lower vehicle. Start engine and run until fuel supply remaining in the fuel pipes is consumed. Engage the starter for 3 seconds to assure the relief of any remaining pressure.
2. Raise vehicle. Connect the fuel pump electrical connector. Lower vehicle. Disconnect negative battery terminal to avoid possible fuel discharge if an accidental attempt to start the engine. WARNING: To reduce the risk of fire and personal injury, relive the fuel system pressure before servicing fuel system components. After reliving system pressure a small amount of fuel may be released when servicing fuel lines or connections. To reduce the chance of personal injury, cover fittings with shop towel before disconnecting, to catch any fuel that may leak out. Place the towel in a approved container when disconnect is completed
3. Remove air cleaner and plug air cleaner (THERMAC) vacuum port on throttle body. Remove steel fuel line between throttle body and fuel filter. When removing fuel line, always use 2 wrenches to prevent damage. Install adapter and fuel pressure gauge between steel line and flexible hose.
4. Start vehicle and observe fuel pressure reading. Fuel pressure should be 9-13 psi (.6-.9 kg/cm 2 ). If fuel pressure is not within specification, go to CHART A-7 in «2.0L(K)/2.5L TESTS W/CODES»(ref-94904) article.
5. Relieve residual pressure as described in step 1). Remove fuel pressure gauge. Reinstall steel line between filter and throttle body. Start engine and watch for leaks. Remove plug from throttle body thermal vacuum port and reinstall air cleaner.

Note. For additional testing and diagnosis information, see TROUBLE SHOOTING in CCC THEORY/OPERATION article in the ENGINE PERFORMANCE Section.

Fuel System Pressure Relief & Test (All Except Skylark 2.5L. VINS A, U)

1. Most TBI models now have a self bleed feature which causes fuel pressure to drop when ignition is off. However, for safety reasons it is recommended that any residual system pressure be removed from system. To do this, remove fuel filler cap to relieve tank vapor pressure. Remove fuel pump fuse from fuse block in passenger compartment. Start and run engine until fuel supply remaining in fuel lines is used. Engage starter again for about 3 seconds. Turn ignition off and reinstall fuse. WARNING: Always relieve residual pressure in fuel delivery system before opening system. To prevent chance of personal injury cover fittings with shop towel while disconnecting fittings.
2. Remove air cleaner and plug air cleaner (THERMAC) vacuum port on throttle body. Remove steel fuel line between throttle body and fuel filter. When removing fuel line, always use 2 wrenches to prevent damage. Install adapter and fuel pressure gauge between steel line and flexible hose.
3. Start vehicle and observe fuel pressure reading. Fuel pressure should be 9-13 psi (.6-.9 kg/cm 2 ). If fuel pressure is not within specification, go to chart A-7 in «2.0L(K)/2.5L TESTS W/CODES»(ref-94904) article.
4. Relieve residual pressure as described in step 1). Remove fuel pressure gauge. Reinstall steel line between filter and throttle body. Start engine and watch for leaks. Remove plug from throttle body thermal vacuum port and reinstall air cleaner.

Note. For additional testing and diagnosis information, see TROUBLE SHOOTING in CCC THEORY/OPERATION article in the ENGINE PERFORMANCE Section

ELECTRONIC CONTROL MODULE (ECM) R & I

Note. Location of ECM varies with model. ECM is usually located within passenger compartment either behind right kick panel or under instrument panel. For exact location refer to component locator chart in appropriate GM CCC article in COMPUTERIZED ENGINE CONTROLS section.

Precautions

When certain materials rub together, a transfer of electrons from one material to another may occur. This results in an electrostatic charge (static electricity) being built up in one of the materials. Since electronic components used in control systems are designed to carry very low voltages, as little as a 30-volt charge created by static electricity can cause a total or degrading failure in ECM or other electronic components. Before servicing ECM, ground yourself and ground the work area to discharge stored electricity.

Removal

Turn ignition switch to "OFF" position. Disconnect negative battery cable from battery. Locate ECM and remove access panels, if any. Remove electrical connectors from ECM. Remove ECM from vehicle. Remove PROM and CALPAC (if equipped) from ECM.

Installation

Install PROM and CALPAC (if equipped) in new ECM. Reinstall ECM into vehicle. Reconnect electrical connectors to ECM. Install access panels. Reconnect negative battery cable to battery.

1. Relieve fuel system pressure. Disconnect negative battery cable. Remove air cleaner and related ducting.
2. Remove electrical connectors from IAC, TPS and fuel injector(s). Lay wiring harness aside.
3. Remove throttle cable, return springs, transmission cable, and cruise control cable (if equipped). Label and remove vacuum hoses.
4. Remove fuel feed and return lines. Use 2 wrenches to prevent fuel nuts in throttle body from loosening. Remove fuel line "O" rings and discard.
5. Remove throttle body retaining bolts. Remove TBI unit and base gasket. Discard base gasket.

1. Using new base gasket, install throttle body unit to intake manifold. Tighten retaining bolts to 16 ft. lbs. (22 N.m). Install new "O" rings onto fuel lines.
2. Connect fuel feed and return lines to throttle body. Use a back-up wrench to prevent fuel line fittings in throttle body from turning. Tighten fuel line nuts to specification. Install vacuum hoses and brackets. To complete installation, reverse removal procedure.

Disconnect negative battery cable at battery. Raise vehicle on hoist. Disconnect electrical connector from oxygen sensor. Carefully remove oxygen sensor from exhaust pipe.

Note. Oxygen sensor may be difficult to remove when engine temperature is less than 120°F (49°C). Excessive removal force may damage threads in exhaust manifold or pipe.

1. Whenever an oxygen sensor is removed, its threads must be coated with anti-seize compound before it is reinstalled. New oxygen sensors will already have this compound applied to threads.
2. Install oxygen sensor in exhaust pipe and tighten sensor to 30 ft. lbs. (41 N.m). CAUTION: Correct torque of O2 sensor is critical to prevent crushing glass beads in graphite anti-seize compound. Crushing glass beads will cause sensor to seize in exhaust manifold, causing necessary replacement of exhaust manifold upon next
3. Reconnect electrical connector to oxygen sensor. Lower vehicle from hoist. Reconnect negative battery cable.

Remove air cleaner and related ducting. Remove IAC electrical connector. Remove IAC retaining screws and remove IAC valve. Replace as necessary.

1. Inspect gasket or "O" ring for damage. Replace as necessary. Measure distance from IAC contact flange to tip of pintle. Distance should not exceed 1 1/8" (28 mm). If valve is extended too far, damage to valve will result during installation.
2. To set IAC pintle length on a new IAC, use finger pressure to slowly retract pintle. Lubricate new "O" ring with transmission oil or install new gasket. Install IAC valve on throttle body. Tighten IAC valve to 13 ft. lbs. (18 N.m). CAUTION: DO NOT extend or retract pintle if IAC valve has been in service or damage to worm gear will result.
3. Connect electrical lead to IAC valve and install air cleaner. Start engine and allow it to reach normal operating temperature. Drive vehicle at least 43 MPH to allow ECM to reset idle speed. It may be necessary to cycle ignition off and restart vehicle before proper idle will be initialized.

Scheme 10

Remove fuel injector retainer screw and retainer. Using screwdriver and fulcrum on side of injector opposite connector terminals, carefully pry injector out. (Scheme 11) Remove upper and lower "O" rings and discard.

1. Lubricate new upper and lower "O" rings with engine oil and place them on injector. Ensure upper ring is in groove and lower ring is flush against filter.
2. Position injector in fuel meter body with electrical connector facing cut-out for wire grommet.
3. Push injector down to seat in cavity. Install injector retainer. Coat injector retainer screw with thread locking compound and install. Tighten screw to 27 INCH lbs. (3.0 N.m).

Scheme 11

Remove air cleaner and disconnect TPS electrical lead. Remove attaching screws, lock washers, retainers and TPS sensor. (Scheme 12) If necessary, remove screw holding TPS actuator lever to end of throttle shaft.

Scheme 12

1. With throttle valve in idle (closed) position, install TPS on throttle body. Ensure that TPS pick-up lever is located above TPS actuator lever. Install retainers, lock washers, and screws using thread locking compound.
2. Connect electrical lead and install air cleaner. With ignition on, connect digital voltmeter to TPS signal and ground terminals. Check TPS voltage with throttle closed. On most engines, TPS is self-zeroing and nonadjustable. After servicing, perform TPS adjustment or nonadjustable TPS output check. See appropriate article in TUNE-UP section. Tighten attaching screws to 18 INCH lbs. (2.0 N.m). To complete installation, reverse removal procedure.

FUEL PUMP R & I

1. Disconnect negative battery cable. Relieve residual pressure from fuel system as described in «FUEL PRESSURE RELIEF & TEST»(/chevrolet/corsica/i-1987-1996/remont/testing-diagnostics/#fuel-injection-system-20l25l-tbi) . Lower fuel tank. Remove fuel lever sending unit and pump assembly.
2. Lift assembly from fuel tank and remove fuel pump from fuel lever 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.

THROTTLE BODY DISASSEMBLY

Disassembly of throttle body unit for immersion in cleaning solvent requires removal of throttle body cover or fuel meter assembly, TPS and IAC assembly. For TPS removal, see THROTTLE POSITION SENSOR (TPS) R & I in this article. For IAC removal see IAC R & I in this article. Throttle valve screws are staked in position and should not be removed.

Scheme 13

FUEL METER ASSEMBLY

Remove fuel meter-to-throttle body retaining screws. Remove fuel meter assembly. Discard gasket. If fuel pressure regulator cover is removed, regulator diaphragm must be replaced to prevent fuel leaks.

CLEANING & INSPECTION

1. Clean all metal parts in a cold immersion-type cleaner such as Carbon X (X-55). Blow dry with compressed air.
2. DO NOT immerse TPS, IAC, throttle body cover, fuel meter cover and pressure regulator assembly, fuel injector, fuel filter, rubber parts and diaphragms in cleaner.
3. Inspect mating surfaces for damage that may prevent gasket sealing. Repair or replace components which may be cause of problems.

1. Install new fuel meter-to-throttle body assembly gasket. Match cut out portions of gasket with openings in throttle body assembly.
2. Place fuel meter assembly on throttle body. Install fuel meter-to-throttle body retaining screws and washers (screws should be coated with locking compound). Tighten screws to 53 INCH lbs. (6.0 N.m).
3. Install new "O" rings on fuel lines. Using a back-up wrench on fuel fittings, tighten fuel line nuts to 20 ft. lbs. (27 N.m). To complete reassembly, reverse disassembly procedure.

TORQUE SPECIFICATIONS

TORQUE SPECIFICATIONS

WIRING DIAGRAMS

For wiring diagrams, see appropriate article in COMPUTERIZED ENGINE CONTROLS section.

See also:
• CCC THEORY/OPERATION
• TROUBLE SHOOTING