Fuel Injection System - Tbi Oldsmobile Cutlass Ciera I

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, fuel pump relay and Throttle Body Injector (TBI) assembly. Air/fuel control system includes Electronic Control Module (ECM), Electronic Spark Timing (EST) System, Idle Air Control (IAC) System, data sensors and emission controls. ECM uses information received from sensors to control air/fuel ratio 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 distributor (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 Injector Assembly

TBI assembly consists of 2 castings, throttle body and fuel meter assembly. Throttle body has throttle valve, Idle Air Control (AC), 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 is a solenoid-operated device controlled by ECM. Fuel is supplied at lower end of injector by fuel delivery system. ECM activates solenoid which lifts normally closed ball valve off its seat. Fuel under pressure is injected in a conical spray pattern at walls of throttle bore, above throttle valve. Excess fuel passes through pressure regulator and is returned to fuel tank.

During engine cranking, fuel injector is pulsed (activated) once for each distributor reference pulse received by ECM. This is referred to as synchronized mode. In non-synchronized mode, injector 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.

Scheme 30

IDLE AIR CONTROL (IAC) SYSTEM

IAC system consists of electrically controlled motor (actuator) which positions IAC valve in air by-pass channel around throttle valve. IAC valve is threaded into throttle body casting. 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 3 different conical IAC pintle designs used. Ensure that correct design and type is used if replacement is made.

ELECTRONIC CONTROL MODULE (ECM)

ECM is the central location in which information from various sensors and controls are gathered. ECM also performs the diagnostic function of 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, correct idle speed and proper spark timing. ECM performs calculations to control the following modes of operation 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 device called a Calibrator or PROM (Programmable Read Only Memory) is used. The PROM is located inside the ECM and contains information pertaining to the vehicles weight, engine, transmission, axle ratio and other powertrain related variables. The PROM is very specific and must be used with the correct vehicle.

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

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 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 below 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 is running above 400 RPM, ECM operates in Open Loop Mode. 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 Mode. In closed loop, ECM controls injector pulse width based upon O2 sensor signals to maintain air/fuel mixture ratio close to 14.7:1.

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.

Coolant Temperature Sensor (CTS)

CTS is located in thermostat housing. Variable resistor (thermistor) sensor transmits electrical signal to ECM proportionate to engine temperature. Low coolant temperature produces high resistance while high coolant temperature produces low resistance.

ECM supplies 5-volt signal to CTS and measures input voltage from CTS. ECM is informed of engine coolant temperature by voltage drop or increase. Coolant temperature is used for fuel management, idle air control, spark timing, EGR operation and other engine operating functions.

Oxygen (O2) Sensor

The O2 sensor is constructed in such way that exhaust gases pass by bottom of sensor. When exposed to O2, sensor produces electrical voltage. This voltage ranges from approximately .1 volt (high O2-lean mixture) to .9 volt (low O2-rich mixture). By comparing amount of O2 present in exhaust gases to amount of O2 in atmosphere, sensor produces signal which is proportional to O2 concentration in exhaust gases. The ECM interprets the electrical signal and adjusts injector pulse width to maintain air/fuel ratio close to 14.7:1.

Manifold Absolute Pressure (MAP) Sensor

MAP sensor is a variable resistance type which measures changes in intake manifold pressure which result from engine load and speed changes.

Pressure measured by MAP sensor is the difference between barometric pressure (atmospheric air) and manifold pressure (vacuum). Closed throttle condition (engine coast down) would produce low MAP reading while wide open throttle condition (engine acceleration) would produce high MAP reading. High value is produced because pressure inside intake manifold (vacuum) is same as pressure outside manifold (atmospheric air).

ECM supplies 5-volt reference signal to MAP sensor. By monitoring sensor output voltage, ECM is informed of intake manifold pressure. Higher pressure (high voltage) requires more fuel, while lower pressure (low voltage) requires less fuel.

Vehicle Speed Sensor (VSS)

This sensor is mounted behind speedometer in instrument cluster. It provides ECM with pulses to determine vehicle speed. This information is used by ECM to control IAC motor.

Note. Vehicle should not be driven without vehicle speed sensor installed.

Throttle Position Sensor (TPS)

TPS is mounted on side of throttle body and is connected to throttle shaft. As throttle valve angle changes, resistance of sensor changes. ECM will calculate fuel requirements based upon throttle valve angle (driver demand).

ECM supplies 5-volt reference signal to TPS. Closed throttle condition produces high resistance at sensor, returning low output signal to ECM (about .5 volts). Wide open throttle condition produces low resistance at sensor, returning high output signal to ECM (almost 5 volts).

Crankshaft Sensor (2.0L & 2.5L)

The crankshaft sensor sends a signal through the DIS module, to ECM. ECM uses this reference signal to calculate engine RPM and to determine crankshaft position.

Distributor Reference Signal (4.3L)

ECM receives signals from distributor that indicate engine RPM and crankshaft position when engine is running.

Direct Ignition System (2.0L & 2.5L)

The Direct Ignition System (DIS) module monitors crankshaft sensor signals and based on these signals sends a reference signal to ECM. DIS monitors the "sync-pulse" to begin ignition firing sequence during cranking.

When engine speed drops below 400 RPM the module controls spark advance by triggering each of 2 coils at a predetermined interval based on engine RPM only. When engine speed is above 400 RPM, ECM controls spark timing. DIS must receive a "sync-pulse" and then a crank signal in that order to enable engine to start.

Note. The DIS module is not repairable, and when being replaced the remaining components must be transferred to new module.

Note. See GENERAL MOTORS COMPUTER COMMAND CONTROL article in COMPUTERIZED ENGINE CONTROL section for further information.

PRELIMINARY CHECKS

Note. For diagnostic flow charts see appropriate article in COMPUTERIZED ENGINE CONTROL section.

Subsystem Checks

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

Determine if fuel control system is operating properly by performing "Field Service Mode" check of DIAGNOSTIC CIRCUIT CHECK. Verify customer complaint. If "engine cranks but will not run", see CHART A-3 in COMPUTERIZED ENGINE CONTROL 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 SYSTEM PRESSURE TEST

Note. For diagnostic flow charts see appropriate article in COMPUTERIZED ENGINE CONTROL section.

1. To relieve any residual system 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 Fuel Pressure Gauge between throttle body and fuel filter.
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 specifications, go to CHART A-7 in COMPUTERIZED ENGINE CONTROL section.
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.

HESITATION, SLUGGISH, SAGS OR POOR MILEAGE

1. Visually check MAP sensor hose for leaks or restrictions (water in hose). Check for correct PROM number. Make sure fuel pressure is a steady 9-13 psi (.6-.9 kg/cm 2 ) at all operating ranges. Ensure base engine timing is correct.
2. With fuel injector electrical connector disconnected, check for fuel leakage from injector while cranking. If leakage occurs, replace injector. Check fuel injector fuel filter for blockage. Check for open in HEI ground circuit.
3. Check operation of A/C compressor control and Torque Converter Clutch (TCC) system. On 2.5L engine, check operation of cooling fan control circuit.
4. Check alternator output voltage. Repair alternator if output is less than 9 volts or greater than 16 volts. Check canister purge system for proper operation. Check EGR system.

CUTS OUT OR STALLS

1. Check for intermittent open circuit or short to ground in the following circuits: HEI reference Purple/White wire, fuel pump circuit Brown wire, injector drive circuits (Light Blue and Light Green wires), IAC drive circuits (Light Blue/White wire, Light Blue/Black wire, Light Green/White wire or Light Green/White wire).
2. Check for restricted fuel filter. Ensure fuel pressure is 9-13 psi (.6-.9 kg/cm 2 ) at all operating ranges. Inspect fuel injector "O" rings for damage. Ensure steel back-up washer is located beneath large "O" ring of fuel injector assembly.

DETONATION (KNOCK)

1. Check for overheating problems due to low coolant level, loose water pump belt, restricted airflow to radiator or restricted coolant flow through radiator. Check for inoperative cooling fan circuit. Check ignition timing.
2. Check for closed EGR system. Check ESC system for no spark retard. Check fuel pressure using CHART A-7 in COMPUTERIZED ENGINE CONTROL section. Remove combustion chamber carbon build up using chemical remover. Check for correct PROM.
3. Check for leaking valve stem oil seals. Check for proper operation of transmission or TCC. Check for incorrect engine basic parts such as cams, heads, pistons, etc. Check for poor fuel quality and proper octane rating.

SURGING

1. Ensure customer understands Transmission Converter Clutch (TCC) and A/C compressor operation. Check alternator output voltage. Repair alternator if output is less than 9 volts or greater than 16 volts.
2. If ALDL tool is available, check that VSS reading matches vehicle speedometer. Check for intermittent EGR at idle. Check for plugged EGR filter.
3. Check for proper operation of ESC. Check ignition timing. Check in-line fuel filter and replace if necessary. Check fuel pressure using CHART A-7 in COMPUTERIZED ENGINE CONTROL section.
4. Check O2 sensor for silicone contamination from fuel or use of improper RTV sealant. O2 sensor may have White, powdery coating resulting in high but false signal voltage (rich exhaust indication). This will cause ECM to reduce fuel delivery to engine, causing surging problem.

HARD STARTING (HOT OR COLD)

1. Ensure that customer is using correct starting procedure. Check for contaminated fuel. Test for high resistance in coolant temperature sensor circuit. Visually check TPS for sticking or binding. Ensure fuel pressure is 9-13 psi (.6-.9 kg/cm 2 ) at all operating ranges.
2. On 2.5L engine, fuel pressure leakdown after ignition is turned off should be gradual. Immediate drop in pressure indicates leaking in-tank fuel pump coupling, hose or check valve. To check for faulty in-tank fuel pump check valve, turn ignition off. Disconnect fuel line at filter and remove fuel tank cap. Connect radiator test pump to line and apply 15 psi (1 kg/cm 2 ). If pressure holds for one minute, check valve is okay.
3. On all engines, check fuel pump relay. Disconnect oil pressure switch. If engine cranks but will not start, perform fuel system diagnosis (at point where fuel pump fuse proves okay). Check injector. With injector harness connector disconnected, check for fuel leakage while cranking. Check cranking circuit.

EXCESSIVE EMISSIONS (ODOR)

1. Check engine for higher than normal CO and HC with engine at normal operating temperature. Check items which may cause engine to run rich. Check fuel pressure using CHART A-7 in COMPUTERIZED ENGINE CONTROL section.
2. Check canister for fuel loading. Check for stuck PCV valve or blocked PCV hose. Check for lead contamination of catalytic converter. Look for removal of fuel filler neck restrictor.

Note. Location of ECM varies with model. ECM is usually located within passenger compartment either behind right kick panel or under instrument panel. On Fiero models, ECM is in center console section between seats.

Removal

Disconnect negative battery cable. Remove interior covering of ECM location. Disconnect ECM electrical leads. Remove ECM and carefully remove PROM from ECM.

Installation

Install old PROM in new ECM. Install ECM and connect leads. Install kick panel. Reconnect battery cable.

Removal & Installation

Remove instrument cluster and speedometer assembly. Disconnect VSS from speedometer. Disconnect VSS electrical connector and remove VSS. To install, reverse removal procedure.

O2 SENSOR

Note. O2 sensor may be difficult to remove when engine temperature

Disconnect battery ground. Disconnect electrical connector. Do not attempt to remove single wire from oxygen sensor. Carefully back sensor out of exhaust manifold. Handle sensor with care and do not allow dirt or other foreign matter to contact louvered end of sensor. To install, reverse removal procedure.

Note. Prior to reinstalling used sensor, coat threads with anti-seize compound.

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

Note. On 4.3L engines, TPS is nonadjustable. After servicing, perform nonadjustable TPS output check. See appropriate article in TUNE-UP section.

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, screws using thread locking compound (Loctite 262), and lock washers.
2. Connect electrical lead and install air cleaner. With ignition on, connect digital voltmeter to TPS "A" and "B" terminals, rotate TPS to obtain .45-.60 volt. Tighten attaching screws and recheck voltage.

1. Disconnect negative battery cable. Relieve residual pressure from fuel system as described in FUEL SYSTEM PRESSURE TEST. 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.

OVERHAUL

Note. Before working on throttle body assembly, it is essential that throttle body be placed on Holding Fixture (J-9789-118 or BT 30-15) to prevent damage to throttle valve.

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, 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 listed under TROUBLE SHOOTING & DIAGNOSIS.

Disassembly

1. Remove air cleaner. Disconnect injector electrical lead by squeezing tabs together and pulling lead straight up. Remove 5 screws holding cover to throttle body, noting location of 2 short screws.
2. Remove throttle body cover. Throttle body cover and pressure regulator are serviced as assembly. DO NOT immerse cover in any type of cleaning solvent.

Scheme 31

Reassembly

1. Install new dust seal into recess of throttle body. Install fuel outlet passage gasket on cover. Install throttle body cover gasket on throttle body. Install cover, making sure that pressure regulator dust seal and cover gaskets are in place.
2. Apply thread locking compound (Loctite 262) to cover attaching screws. Install cover screws and lock washers. Tighten screws. Connect electrical lead to fuel injector and install air cleaner.

1. Disassembly of throttle body unit for immersion in cleaning solvent requires removal of TPS and IAC assembly. Throttle valve screws are staked in position and should not be removed. If necessary to remove TPS, continue as follows
2. Invert throttle body assembly and place on clean, flat surface. Remove and discard 2 TPS attaching screws, lock washers and retainers. Remove TPS from throttle body. (Scheme 32)
3. If necessary, remove screw holding TPS actuator lever to throttle shaft. Remove IAC assembly from throttle body. Remove and discard IAC gasket.

Removing TPS Assembly Invert throttle body unit to remove TPS. Scheme 32

Scheme 33

1. Measure distance that IAC valve is extended from motor housing. Measuring from gasket mounting surface of housing to end of pintle, distance should not exceed 1 1/8" (28 mm). If valve is extended too far, damage will result to valve during installation.
2. Identify IAC valve as being Type 1 (collar at electrical end) or Type 2 (without collar). (Scheme 33) If valve was extended greater than 1 1/8", reduce distance as explained in step 3).
3. On Type 1 (collar at connector) IAC valve, push pintle inward with slight side-to-side motion. On Type 2 (no collar at connector) IAC valve, compress pintle retaining spring toward IAC body while turning pintle inward with clockwise motion. On IAC valves without collar, return spring to original position with straight portion of spring end aligned with flat surface under pintle head.
4. Lubricate new "O" ring with transmission oil and install IAC valve on throttle body using new gasket. Tighten IAC valve. Connect electrical lead to IAC valve and install air cleaner. Start engine and allow it to reach normal operating temperature. Drive vehicle at least 40 MPH to allow ECM to reset idle speed.

Note. TPS adjustment must be done with throttle body installed on vehicle. See appropriate article in TUNE-UP section.

Reassembly - Throttle Position Sensor (TPS)

Place throttle valve in normal closed idle position. Install TPS on throttle body with pick-up lever above throttle actuator lever. Install retainer, lock washers and 2 new attaching screws (coated with locking compound).

Note. Use care in removing injector to prevent damage to electrical connectors, fuel filter and nozzle. Injector is serviced only as unit.

1. Remove throttle body cover and leave cover gasket in place. Using screwdriver and fulcrum, carefully pry injector out. Remove small "O" ring from nozzle end of injector. (Scheme 34)
2. Carefully rotate injector fuel filter back and forth to remove fuel filter from base of injector. Remove and discard throttle body cover gasket. Remove large "O" ring and steel back-up washer from top counterbore of throttle body injector cavity.

Scheme 34

1. Install fuel filter on nozzle end of fuel injector. Large end of filter must face injector so that filter covers raised rib at base of injector. Lubricate small "O" ring with Automatic Transmission Fluid (ATF) and push "O" ring on nozzle end of injector until it presses against injector filter.
2. Install steel back-up washer in top counterbore of throttle body injector cavity. Lubricate large "O" ring with ATF and install "O" ring directly over back-up washer. (Scheme 31) Ensure that "O" ring is seated properly in cavity and is flush with top of throttle body casting. CAUTION: Back-up washer and large "O" ring must be installed before injector. Improper seating of "O" ring may cause fuel to leak.
3. Install "O" ring on injector. Install injector into cavity by aligning raised lug on injector base with cast-in notch of throttle body cavity. Push down on injector until it is fully seated. Electrical terminals of injector will be approximately parallel with throttle shaft. Install throttle body cover.

Scheme 35

TORQUE SPECIFICATIONS

TORQUE SPECIFICATIONS

2.0L OHC (VIN K) Throttle Body Fuel Injection Wiring Diagram. Scheme 36

2.0L OHV (VIN 1) Throttle Body Fuel Injection Wiring Diagram. Scheme 37

2.0L OHV (VIN K) Throttle Body Fuel Injection Wiring Diagram. Scheme 38

2.5L (VIN U) Throttle Body Fuel Injection Wiring Diagram. Scheme 39

2.5L (VIN R) Throttle Body Fuel Injection Wiring Diagram. Scheme 40

4.3L Throttle Body Fuel Injection Wiring Diagram. Scheme 41