Fuel Injection System - Tbi Pontiac 6000 I

COMPONENT TESTING

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

APPLICATION

ROCHESTER THROTTLE BODY NUMBER

IDENTIFICATION

An 8-digit unit identification number is stamped on throttle body assembly for servicing or replacement reference. On Model 220, number is stamped vertically on front of body at Throttle Position Sensor (TPS) side. On Model 300, number can be found on throttle lever side of mounting flange. On Model 500, number can be found on TPS side of mounting flange. (Scheme 16) Letter codes are stamped on throttle body at external tube locations to identify vacuum hose connections.

Single Injector Throttle Body Identification Location This number should be used for service or replacement information. Scheme 16

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 on, fuel pump relay activates fuel pump for 1 1/2-2 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 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 is composed of 2 castings: throttle body with valve to control air flow and fuel body with integral pressure regulator and fuel injector. Throttle body casting may contain ports to generate vacuum signals for EGR valve, MAP sensor and canister purge system.

Pressure regulator is diaphragm-operated relief valve with injector pressure acting on one side of valve and air cleaner pressure acting on other side of valve. Pressure regulator maintains constant pressure drop of about 10 psi (.7 kg/cm 2 ) across injector, throughout all engine operating conditions. (Scheme 17)

Sectional View of Throttle Body Assembly. Scheme 17

Fuel injector is 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 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 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.

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.

If engine speed is lower than desired, ECM activates IAC motor to retract IAC valve. When IAC valve is retracted, more air is diverted around throttle valve to increase engine speed. If engine speed is higher than desired, ECM activates IAC motor to extend IAC valve. When IAC valve is extended, less air is diverted around throttle valve, decreasing engine speed. If engine speed falls below preset level and throttle valve is closed, ECM senses near stall condition. To prevent stalling, ECM will calculate IAC valve position based upon barometric pressure.

There are 3 different conical IAC valve designs used. First is 35° single taper. Second design, used on 4.3L engines with A/T, is dual taper. Third design is blunt. Ensure that correct design is used if replacement is made.

ELECTRONIC CONTROL MODULE (ECM)

ECM is located in passenger compartment and is "brain" of both EFI and Computer Command Control systems. Locations vary, but ECM is generally located under instrument panel behind glove compartment or behind passenger footwell kick panel.

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 following modes of operation: starting, clear flood, run, acceleration, deceleration, battery voltage correction and fuel cut-off.

ECM's have "learning process" capacity. If battery is disconnected, process must begin all over again. During this period, change may be noted in vehicle performance. To "teach" vehicle, ensure vehicle is at normal operating temperature. Vehicle should then be driven at part throttle with moderate acceleration and idle until performance returns.

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 220°F (104°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 enough to set 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 600 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 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, air/fuel mixture must be leaner. 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 to remove fuel from engine. 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

Battery voltage corrections by ECM are performed during all operating modes of EFI system. As battery voltage decreases, ECM increases injector pulse width with correction factor stored in ECM's memory.

Fuel Cut-Off

No fuel is delivered when ignition is off so that dieseling is prevented. No fuel will be delivered if no reference pulses are sent by distributor. This will prevent flooding before starting.

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 between 2 readings. Coolant temperature is used for fuel management, idle air control, spark timing, EGR operation, canister purge operation and other engine operating functions.

Oxygen (O2) Sensor

O2 sensor used in EFI system is closed-end Zirconia sensor placed in exhaust gas stream. Sensor is constructed in such way that exhaust gases pass by bottom of sensor and atmospheric air is admitted at top of sensor.

When exposed to O2, Zirconia produces electrical voltage of approximately 1.5 volts. 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.

As O2 content of exhaust gases increases relative to surrounding atmosphere, lean fuel mixture is indicated by low voltage output. As O2 content decreases, rich fuel mixture is indicated by higher voltage output. ECM interprets electrical signal and adjusts injector pulse width to maintain air/fuel ratio close to 14.7 to 1.

Electrically Heated O2 Sensor

Electrically heated O2 sensor is used on 4.3L engine. This sensor is energized by fuel pump relay and remains on as long as engine is running. Failure of heating element, power feed or ground circuit may cause Code 13 to be set at idle or low RPM.

Note. No attempt should be made to measure O2 sensor voltage output. Current drain of conventional voltmeter could permanently damage sensor, shift sensor calibration and/or render sensor unusable. DO NOT connect jumper wire, test leads or other electrical connectors to sensor.

Manifold Absolute Pressure (MAP) Sensor

MAP sensor is mounted on right side of engine compartment. This sensor is variable resistance type which measures changes in intake manifold pressure which result from engine load and speed changes.

Pressure measured by MAP sensor is 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. As MAP changes, electrical resistance of sensor also changes. 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).

Engine Speed Sensor

Engine speed signal comes from Hall Effect unit mounted above distributor on 2.5L engine and from terminal "R" of conventional HEI module in distributor on all other models. It is not "sensor" in that it is not separate component.

Pulses from distributor are sent to ECM where time between these pulses (dwell) is used to calculate engine speed. ECM sends spark advance modification signal back to distributor.

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

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.

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 this article.

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

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 or short to ground in the following circuits: 5-volt reference (416), HEI reference (430), fuel pump circuit (120), injector drive circuits (467 and 468), IAC drive circuits (441, 442, 443 or 444).
2. Check for restricted fuel filter. Make sure 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 air flow 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 this article. 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 this article.
4. Check O2 sensor for silicon 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 water 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 1 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 this article.
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.

FUEL SYSTEM PRESSURE TEST

1. To relieve any residual system pressure, remove "FUEL PUMP" fuse from fuse block in passenger compartment. Crank engine. Engine will start and run until fuel supply remaining in fuel lines is used. Engage starter again for about 3 seconds to make sure all fuel is out of lines. Turn ignition off and replace fuse.
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 (J-29658) 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-5 or CHART A-6 in this article. 4) Relieve residual pressure as described in step 1). Remove fuel pressure gauge. Reinstall steel line between filter and throttle body. Start vehicle and watch for leaks. Remove plug from throttle body thermal vacuum port and reinstall air cleaner.

CHART A-3

Engine cranks but will not run or engine may start, but immediately stop running. Battery condition and cranking speed are okay. There is enough fuel in gas tank.

Note. Test numbers refer to test numbers on diagnostic charts.

1. "CHECK ENGINE" light "ON" checks for ignition and battery supply to ECM.
2. Fuel spray from injector indicates that fuel is available, check engine for flooding.
3. While cranking engine there should be no fuel spray with injector disconnected. Replace injector if it sprays or if it drips.
4. At this point, fuel system appears to be operating properly. Using Spark Gap Tool (ST-125), check voltage at spark plugs. No spark indicates HEI problem. If spark is satisfactory, check following: Throttle Position Sensor (TPS) for sticking or binding in wide open throttle position. ECM will be in "CLEAR FLOOD" mode. Check coolant sensor. If sensor signal circuit opens with ignition, off, ECM will think coolant temperature is below -40°F (-4°C). ECM will provide fuel for this temperature and flood engine as it will not recognize open circuit until engine has run for 1 minute or more. Check circuit using Code 15 chart. See GENERAL MOTORS COMPUTER COMMAND CONTROL SYSTEM in COMPUTERIZED ENGINE CONTROLS section.
5. EFI system is considered okay, if no trouble was found. Reconnect Injector and look for possible mechanical problems.
6. No fuel spray from injector indicates faulty fuel system or no ECM control of injector. If test light "blinks" while cranking, ECM control is considered okay. Light may dim while "blinking", use bulb 1847 or equivalent.

Chart A-3, Engine Cranks But Will Not Run (1 of 2). Scheme 18

Chart A-3, Engine Cranks But Will Not Run (2 of 2). Scheme 19

CHART A-4

Note. Test numbers refer to test numbers on diagnostic chart.

1. No fuel spray from injector indicates faulty fuel system or no ECM control of injector. If test light "blinks" while cranking, ECM control is considered okay. Light may dim while "blinking", use bulb 1847 or equivalent.
2. Circuits 481 and 482 supply ignition voltage to injectors. Probe Each connector terminal with test lamp connected to ground. There should be light on one terminal. If test lamp confirms ignition voltage at connector, then ECM injector control circuit 467 or 468 may be open. Reconnect injector and using test lamp connected to ground, check for light at applicable ECM connector (terminal D14 or D16). Light at this point indicates that injector drive circuit involved is okay. If ECM repeat failure has occurred, injector is shorted. Replace injector and ECM.

Chart A-4, Engine cranks but will not run. Scheme 20

CHART A-5 & A-6, FUEL SYSTEM DIAGNOSIS

ECM turns in-tank fuel pump on as long as ignition is on and engine is cranking or running. ECM will allow pump to run as long as it receives reference pulses from distributor. If there are no reference pulses, ECM will shut off fuel pump within 2 seconds after key is on.Fuel pump test terminal is located on left side of engine compartment. When engine is stopped, pump can be turned on by applying battery voltage to test terminal. Improper fuel system pressure will result in one or all of following symptoms: Cranks but will not run, Code 44, Code 45, engine cuts out (may feel like ignition problem), poor fuel economy, loss of power and hesitation.

Note. Test numbers refer to test numbers on diagnostic charts.

1. If fuse is blown, this test will confirm short to ground on circuit 120. To prevent mis-diagnosis, be sure fuel pump is disconnected before test.
2. This test determines if pump circuit is ECM controlled. ECM will turn pump relay on, then turn it off within 2 seconds after ignition is turned on.
3. This step turns fuel pump on, if circuit 120 wiring is okay.
4. This step checks for battery voltage at fuel pump relay.
5. This step checks relay ground circuit 450.
6. This step checks ECM control of relay through circuit 465.
7. Fuel pump circuit includes engine oil pressure switch. If fuel pump relay fails, fuel pump will continue to run via oil pressure switch circuit. Relay failure will result in extended cranking times and possible no start condition.
8. This test checks oil pressure switch to be sure it provides battery feed to fuel pump if pump relay fails.
9. This test checks for open oil pressure switch with ignition off. Should switch stick closed, fuel pump will continue to run and discharge battery.

Chart A-5, Fuel System Diagnosis. Scheme 21

Chart A-6, Fuel System Diagnosis. Scheme 22

CHART A-7

Note. Test numbers refer to test numbers on diagnostic charts.

1. Pressure below 9 psi falls into 2 categories: If regulated pressure is less than 9 psi and volume to injector adequate, system will run lean and cause Code 44. Engine will be hard to start when cold and have poor overall performance. Restricted fuel flow is causing pressure drop. Normally, vehicle with fuel pressure of less than 9 psi at idle will not be driveable.However, if pressure drop occurs only when driving, engine will surge then stop as pressure begins to drop.
2. Restricting fuel return line allows fuel pump to develop maximum pressure. When battery voltage is applied to pump test terminal, pressure applied to pump test terminal, pressure should be between 13 to 18 psi.
3. This test determines if high fuel pressure is due to restricted fuel return line or throttle body pressure regulator problem.

Chart A-7, Fuel System Diagnosis. Scheme 23

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 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 is below 120°F (48°C). Excessive force can damage threads.

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 liquid graphite compound containing glass beads. This is special anti-seize compound.

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

1. With throttle valve in idle (closed) position, install TPS on throttle body. Ensure that TPS pickup 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 volts. Tighten attaching screws and recheck voltage.

1. Disconnect negative battery cable. Relieve residual pressure from fuel system as described in «FUEL SYSTEM PRESSURE TEST»(/pontiac/6000/i-1982-1991/remont/testing-diagnostics/#fuel-injection-system-tbi__fuel-system-pressure-test) . Lower fuel tank. Remove fuel lever sending unit and pump assembly by turning cam lock ring counterclockwise.
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.

DISASSEMBLY

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.

Throttle Body Cover

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.

Exploded View of Rochester Single Unit Throttle Body Assembly. Scheme 24

Throttle Body

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 19)
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 25

Throttle Body Injector

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 20)
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.

Throttle Body Fuel Injector Removal. Scheme 26

CLEANING & INSPECTION

1. Clean all metal parts in a cold immersion-type cleaner and 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»(/pontiac/6000/i-1982-1991/remont/testing-diagnostics/#fuel-injection-system-tbi) .

Scheme 27

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 21) If valve was extended greater than 1 1/8", reduce distance as explained in step 3). (Scheme 27): Idle Air Control (IAC) Valve Identification
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. 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 30 MPH to allow ECM to reset idle speed.

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

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 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 18) 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.

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.

Model 220 Throttle Body Injection Assembly This model is used on 4.3L engine. Scheme 28

TORQUE SPECIFICATIONS

TORQUE SPECIFICATIONS

1.8L & 2.5L Throttle Body Fuel Injection Wiring Diagram. Scheme 29

2.0L Throttle Body Fuel Injection Wiring Diagram. Scheme 30

4.3L Throttle Body Fuel Injection Wiring Diagram. Scheme 31

See also:
• FUEL SYSTEM PRESSURE TEST
• TROUBLE SHOOTING