Fuel Injection System - Single Unit Tbi Chevrolet Camaro II

COMPONENT TESTING

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

APPLICATION

ROCHESTER THROTTLE BODY NO.

IDENTIFICATION

The throttle body identification number is "roll-stamped" on the front mounting flange on the throttle lever side (Model 300) or throttle position sensor side (Model 500) of the throttle body. (Scheme 21) Alphabetical code letters are stamped on the throttle body at external tube locations to identify vacuum hose connections.

Throttle Body Identification Location This number should be used for service information. Scheme 21

DESCRIPTION

The General Motors single unit Electronic Fuel Injection (EFI) system consists of 7 major sub-assemblies: fuel supply system, Throttle Body Injector (TBI) assembly, Idle Air Control (IAC) system, Electronic Control Module (ECM), Electronic Spark Timing (EST), data sensors and emission controls.

The Model 300 TBI assembly is used on 1.8L and 2.5L engines. The Model 500 TBI unit is used only on the 2.0L engine. The major difference between the 2 models is that the Model 500 has the Throttle Position Sensor (TPS) and throttle lever located on opposite sides from the Model 300.

Fuel is supplied to engine through an electronically pulsed (timed) injector valve located in throttle body unit on top of intake manifold. The ECM controls amount of fuel metered through injector valve based upon engine demand and efficiency information. The ECM is a digital electronic computer which receives and computes signals from various data sensors.

Note. Primary sub-systems which affect fuel system operation will be covered in this article: fuel supply system, TBI assembly, IAC assembly, ECM and data sensors. Because of the interrelated functions of the Computer Command Control (CCC) system (the ECM is the "brain"), refer to COMPUTER COMMAND CONTROL in COMPUTERIZED ENGINE CONTROLS section for more information.

FUEL SUPPLY SYSTEM

An electric fuel pump (located inside fuel tank as an integral part of fuel gauge sending unit) supplies fuel under pressure to throttle body. A fuel pump relay located on the left or right side of the engine compartment controls fuel pump operation. When the ignition is turned on, the fuel pump relay activates the fuel pump for 1 1/2-2 seconds to prime the injector. If the ECM does not receive reference pulses from the distributor after this period, the ECM deactivates the fuel pump circuit. The fuel pump relay will be activated again when the ECM receives distributor reference pulses.

THROTTLE BODY INJECTOR (TBI) ASSEMBLY

The TBI assembly consists of 2 castings: a throttle body with a valve to control airflow and a fuel body with an integral pressure regulator and fuel injector. The throttle body casting may contain ports to generate vacuum signals for EGR valve, MAP sensor and canister purge system.

The pressure regulator is a diaphragm-operated relief valve with injector pressure on one side and air cleaner pressure on the other side. The pressure regulator maintains a constant pressure drop of about 10 psi (.7 kg/cm 2 ) across the injector throughout all engine operating conditions. (Scheme 22)

Sectional View of Throttle Body Assembly This view applies to both the Model 300 and Model 500 throttle body assemblies. Scheme 22

The fuel injector is a solenoid-operated device controlled by the ECM. Fuel is supplied at the lower end of the injector by the fuel supply system. The ECM activates the solenoid which lifts a normally closed ball valve off its seat. Fuel under pressure is injected in a conical spray pattern at the walls of the throttle bore above the throttle valve. Excess fuel passes through the pressure regulator and is returned to fuel tank.

During engine cranking, the fuel injector is pulsed (activated) once for each distributor reference pulse received by the ECM. This is referred to as the synchronized mode. In the non-synchronized mode, the injector is pulsed once every 6.25-12.50 milliseconds depending upon engine calibration and operating conditions. In this mode, the pulse is totally independent of distributor reference pulses.

IDLE AIR CONTROL (IAC) ASSEMBLY

The IAC assembly consists of an electrically controlled motor which positions the IAC valve in the air by-pass channel around the throttle valve. The IAC valve is a part of the throttle body casting. The ECM calculates the desired position of the IAC valve based upon battery voltage, coolant temperature, engine load and engine speed to control idle speed while preventing stalls due to engine load changes.

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

Three different designs of IAC pintle valves are used. The first design is a single 35° taper, the second is a dual taper and the third is a blunt type. (Scheme 23) Care should be used to ensure correct replacement during service.

Idle Air Control Pintle Valve Design Ensure correct replacement is used during service. Scheme 23

ELECTRONIC CONTROL MODULE (ECM)

The ECM is located in the passenger's compartment and is the "brain" of the EFI system and Computer Command Control system. Locations vary, but the ECM is generally located under the instrument panel behind the glove compartment or behind the passenger footwell kick panel. Information from all data sensors is received and processed by the ECM to produce proper pulse duration ("on" time) for the injector, correct idle speed and proper spark timing. The ECM performs calculations to control the following EFI operating conditions: engine start, engine flooding, engine running, fuel enrichment during acceleration, lean fuel mixture during deceleration, fuel cutoff and battery voltage correction.

During engine starts, the ECM delivers an injector pulse for each distributor reference pulse received (synchronized mode). The injector pulse width is based upon coolant temperature and throttle position. The air/fuel ratio is determined by the 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). The lower the coolant temperature, the longer the injector pulse width (richer air/fuel ratio). The higher the coolant temperature, the shorter the injector pulse width (leaner air/fuel ratio).

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

When the engine is running above 600 RPM, the ECM operates in the open loop mode. In open loop, the ECM calculates injector pulse width based upon coolant temperature and manifold absolute pressure (MAP). The engine will remain in open loop operation until the oxygen sensor reaches operating temperature, coolant temperature reaches a preset temperature and a specific period of time elapses after engine start. When all these conditions are met, the ECM operates in the closed loop mode. In closed loop, the ECM controls the injector pulse width according to oxygen sensor signals to maintain the air/fuel ratio at 14.7:1. In either mode, the injector is pulsed once for each distributor reference.

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

During normal deceleration, the air/fuel mixture must be leaner. The ECM calculates the injector pulse width similar to that during fuel enrichment. Fuel output is reduced due to fuel remaining in the intake manifold. During sudden deceleration, when MAP, throttle position and engine speed are reduced to preset levels, fuel flow is cutoff completely to remove fuel from the engine. This deceleration fuel cutoff overrides the normal deceleration mode. During either deceleration mode, the injector pulses are not in proportion to distributor reference signals.

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

DATA SENSORS

Each sensor furnishes an electrical signal to ECM, modifying injector pulse to conform to engine operating conditions. These sensors are as follows

Coolant Temperature Sensor (CTS)

The CTS is located in the thermostat housing. This sensor is a variable resistor (thermister) type which transmits an electrical signal (proportionate to engine temperature) to the ECM.

Oxygen Sensor

The oxygen sensor is mounted in the exhaust manifold. This sensor is similar to a small battery. The voltage output of the sensor indicates to the ECM the amount of oxygen in the exhaust gases. The ECM corrects the air/fuel ratio according to signals received by the oxygen sensor only when the system is operating in closed loop.

Manifold Absolute Pressure (MAP) Sensor

The MAP sensor is mounted on the right side of the engine compartment or on the air cleaner. This sensor is a variable resistor type which has a vacuum hose connected to the throttle body. The sensor monitors changes in intake manifold pressure which result from engine load and speed changes. As MAP changes, the electrical resistance of the sensor changes. The ECM uses the resistance value of the sensor to control injector pulse width. The MAP sensor also allows for altitude compensation of the air/fuel ratio.

Vehicle Speed Sensor (VSS)

The VSS is mounted behind the speedometer in the instrument cluster. This sensor provides the ECM with pulses to determine vehicle speed. This information is used by the ECM to control the IAC assembly, canister purge and torque converter clutch.

Note. Vehicle should not be driven without the VSS installed.

Throttle Position Sensor (TPS)

The TPS is mounted on side of throttle body and connected to throttle shaft. This sensor converts throttle angle to an electrical signal for use by the ECM to determine engine fuel requirements.

Engine Speed Sensor

The engine speed signal comes from the Hall Effect Unit mounted above the distributor on the 2.5L engine and from terminal "R" of the conventional HEI module in the distributor on all other models. Pulses from the distributor are sent to the ECM where the time between these pulses is used to calculate engine speed. The ECM adds spark advance modifications to the signal and sends the signal back to the distributor.

Note. More sensors are used by the ECM to control engine performance and other systems. Refer to COMPUTER COMMAND CONTROL in COMPUTERIZED ENGINE CONTROLS section for more information.

PRELIMINARY CHECKS

The following systems and components must be in good condition and operating properly before beginning diagnosis of the fuel injection system

1. All support systems and wiring.
2. Battery connections and specific gravity.
3. Ignition system.
4. Compression pressure.
5. Fuel sypply system pressure and flow.
6. All electrical connections and terminals.
7. Vacuum line, fuel hose and pipe connections.

Note. Trouble shooting and diagnosis of fuel system should begin with determining fuel system pressure. Before performing any test on the fuel system, pressure must be released from the system.

FUEL SYSTEM PRESSURE TEST

1. 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 assure all fuel is out of lines. Turn ignition off and replace fuse.
2. Remove air cleaner and plug thermal vacuum port on throttle body. Remove steel fuel line between throttle body and fuel filter. When removing fuel line, always use 2 wrenches. Install a Fuel Pressure Gauge (J-29658 or equivalent) between throttle body and fuel filter.
3. Start car and observe fuel pressure reading. Use Fuel System Diagnosis chart if pressure is not between 9-13 psi (.6-.9 kg/cm 2 ). Use Injector System Diagnosis chart if pressure is between 9-13 psi (.6-.9 kg/cm 2 ).
4. Depressurize fuel system as described in step 1). Remove fuel pressure gauge and reinstall steel line between filter and throttle body. Start car and watch for leaks. Remove plug from throttle body thermal vacuum port and reinstall air cleaner.

HESITATES, SLUGGISH, SAGS OR POOR MILEAGE

1. Visually check vacuum hoses for leaks, restrictions and proper routing. Check for air leaks around throttle body mounting and intake manifold. Check spark plugs, ignition wiring, ignition timing and idle speed.
2. Check air cleaner damper door operation. Visually check air cleaner and air filter for dirt and clogging. Check EGR and EST operation. Check MAP sensor output. Check exhaust system for restrictions. With injector connector disconnected, check for fuel leakage from injector while cranking.
3. Ensure fuel pressure is steady 9-13 psi (.6-.9 kg/cm 2 ) at all operating ranges. Visually check TPS for sticking or binding. With injector electrical connector disconnected, check for fuel leakage from injector while cranking.
4. Check for open HEI ground (circuit 453). Check fuel injector fuel filter for blockage. Check fan control circuit (if equipped). Check A/C compressor control and torque converter clutch (TCC) system. Refer to COMPUTER COMMAND CONTROL in COMPUTERIZED ENGINE CONTROLS section for testing procedures.

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. 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.

SURGE

Check for intermittent open or short to ground in the following circuits: transmission converter clutch (420 and 422), HEI bypass (424), EST (423). Refer to COMPUTER COMMAND CONTROL in COMPUTERIZED ENGINE CONTROLS section for testing procedures.

HARD STARTING (HOT OR COLD)

1. 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. An instant drop in pressure indicates a leaking in-tank fuel pump coupling, hose or check valve.
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).
4. Check injector. With injector harness connector disconnected, check for fuel leakage while cranking. Check cranking circuit. Refer to COMPUTER COMMAND CONTROL in Computerized Engine Controls Section for testing procedure.

FUEL SYSTEM DIAGNOSIS

Note. EFI system under pressure, to avoid fuel spillage

Chart 5A (1 of 2) Fuel System Diagnosis. Scheme 24

Chart 5A (2 of 2) Fuel System Diagnosis. Scheme 25

This procedure assumes that the "CHECK ENGINE" light is functioning and is on.

Injector System Diagnosis (1 of 2). Scheme 26

Injector System Diagnosis (2 of 2). Scheme 27

Note. Location of ECM varies between model application. ECM is located within passenger compartment either behind right kick panel or under instrument panel.

Removal & Installation

Disconnect negative battery cable. Disconnect 2 electrical connectors from ECM. Remove ECM mounting hardware and ECM. To install, reverse removal procedure.

Fuel pump relay is located on left or right side of engine compartment. Relay is mounted in area of brake master cylinder and is closest relay to fender (for left installation). If relay is mounted on right side, fuel pump relay is nearest firewall. Remove electrical connector, mounting screws and relay. To install, reverse removal procedure.

Removal and Installation

MAP sensor is located in engine compartment. Location varies between application, but is generally mounted on air cleaner. Remove vacuum hose, mounting screws and MAP sensor. To install, reverse removal procedure.

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

Disconnect electrical connector and remove CTS. To install, reverse removal procedure.

Note. Handle CTS with care to prevent damage to sensor calibration.

Note. Oxygen sensor may be difficult to remove when engine temperature is below 120°F (49°C). Excessive force may damage threads.

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 a serviceable sensor, coat threads with liquid graphite compound containing glass beads (special anti-seize compound).

Disconnect negative battery cable. Remove pressure from fuel lines as described under Fuel Pump Pressure Test. Remove fuel lines. Lower fuel tank. Remove attaching screws and fuel pump. To install, reverse removal procedure.

Removal

1. Relieve pressure from fuel lines as explained under Fuel Pump Pressure Test. Remove air cleaner. Disconnect throttle linkage, return spring and cruise control linkage (if equipped). Disconnect and identify all electrical connectors from throttle body.
2. Disconnect and identify all vacuum hoses from throttle body for installation reference. Disconnect fuel lines from throttle body using 2 wrenches. Remove 3 throttle body-to-manifold bolts. Model 500 uses 2 long bolts to secure air cleaner isolator and 1 throttle body-to-manifold bolt. Remove throttle body.

Installation

To install, reverse removal procedure and note the following: Ensure throttle body and intake manifold sealing surfaces are clean. Always use new throttle body-to-manifold gasket.

ADJUSTMENTS

Note. See appropriate article in TUNE-UP section.

DISASSEMBLY

Note. Before performing any service on throttle body assembly, it is essential that throttle body be placed on a Holding Fixture (J-9789-118, BT 30-15 or equivalent) to prevent damage to throttle valve. Disassembly of each throttle body unit is the same. DO NOT interchange components between front and rear units. Mark and identify each component for identification.

Fuel Meter Cover

1. Remove 5 cover-to-meter body screws and lock washers. Lift off fuel meter cover with fuel pressure regulator assembly (rear unit) or accumulator assembly (front unit) attached. DO NOT remove fuel meter cover gasket at this time. (Scheme 24)and (Scheme 25). WARNING: DO NOT remove 4 screws attaching pressure regulator (accumulator) to fuel meter cover. The regulator (accumulator) includes a spring under heavy tension which may cause personal injury if released. Fuel meter cover and pressure regulator (accumulator) are serviced as an assembly only. DO NOT immerse assembly in any type of cleaning solvent.
2. Remove fuel pressure regulator (rear unit) or accumulator (front unit) dust seal from fuel meter body.

Fuel Meter Cover Assembly Removal Do not remove fuel meter cover gasket at this time. Scheme 28

Fuel Injector

1. With fuel meter cover gasket in place, use a screwdriver to carefully pry the injector from the fuel metering body. Carefully lift injector out with a twisting motion. Remove fuel meter cover gasket. (Scheme 26) NOTE: Use care in removing injector to prevent damage to electrical connectors, fuel filter and nozzle. Injector is serviced as complete assembly only. Injectors are not interchangeable between front and rear units.
2. Carefully rotate injector filter back and forth to remove from base on injector. Remove large "O" ring and steel back-up washer on top of injector cavity in fuel meter body. Remove small "O" ring at bottom of injector cavity.

Fuel Injector Assembly Removal Keep fuel meter cover gasket in place until injector is removed to prevent damage to casting. Scheme 29

Fuel Meter Body

Remove fuel inlet and outlet nuts and gaskets from fuel meter body. Remove air cleaner stud (if equipped). Remove 3 fuel meter body-to-throttle body screws and lock washers. Remove fuel meter body and gasket.

Throttle Body

1. Disassembly of throttle body unit for immersion in cleaning solvent requires removal of TPS (rear unit) and IAC assemblies. 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 TPS attaching screws. Remove lock washers, retainers and TPS from throttle body. (Scheme 28)
3. If necessary, remove TPS actuator lever-to-throttle shaft screw. Remove IAC assembly and gasket from each throttle body. Remove and discard IAC gaskets.

TPS Assembly Removal (Rear Unit Only) Invert throttle body to remove TPS. Scheme 30

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 (accumulator) 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 and Diagnosis.

Place throttle body on holding fixture. Install IAC assembly with new gasket. Tighten securely. Install TPS actuator lever by aligning flats on lever with flats on end of shaft. DO NOT install TPS until complete assembly of rear throttle body assembly.

Note. Before installing IAC assembly, measure distance that valve extends from motor housing. Measuring from end of housing to end of cone, distance should not exceed 1 1/8" (28 mm). If not to specification, push pintle inward (IAC valve with collar on electrical connector) or compress pintle retaining spring toward IAC body while turning pintle inward with a clockwise motion (IAC valve without collar on connector). On IAC valves without collar, return spring to original position with straight portion of spring end aligned with flat surface under pintle head.

1. Install fuel meter body gasket on throttle body. Cutout portions of gasket must match cutouts on throttle body. Install fuel meter body on gasket.
2. Apply thread locking compound (supplied in service kit) on 3 attaching screws. Install lock washers and screws. Tighten screws. Install fuel inlet and outlet nuts with new gaskets.

1. Using a slight twisting motion, install fuel injector filter on nozzle end of injector until seated against injector base. NOTE: Filter is cone-shaped. Large end of filter points up toward injector electrical connectors. Filter should cover raised rib at base of injector.
2. Lubricate "O" rings with automatic transmission fluid. Push small "O" ring on nozzle end of injector until seated against injector fuel filter. Install steel back-up washer in recess in injector cavity of fuel meter body.
3. Install large "O" ring directly above back-up washer. Press "O" ring down in cavity recess until flush with top of fuel meter body casting surface. (Scheme 29) NOTE: "O" rings and back-up washer must be installed in this manner. DO NOT attempt to seat "O" rings and washer after injector is placed in cavity.
4. Using a pushing/twisting motion, install injector in cavity. Align raised lug on injector base with notch in fuel meter body. Push down on injector to center "O" ring in bottom of cavity and to seat injector.
5. Injector is correctly installed when lug on injector is seated in fuel meter body notch and electrical connections are parallel to throttle shaft in throttle body.

Note. Insure injectors and components are installed in their original throttle body. DO NOT interchange components between front and rear units.

Fuel Injector Installation Lubricate "O" rings with automatic transmission fluid. Scheme 31

Exploded View of Rochester Single Unit Throttle Body Assembly. Scheme 32

1. Install new fuel pressure regulator dust seal in fuel meter body recess in rear unit. Install new fuel return passage gasket. Install new fuel meter cover gasket on fuel meter body.
2. Install fuel meter cover with pressure regulator on rear unit. Install fuel meter cover with accumulator on front unit. Apply thread locking compound (supplied in service kit) to 5 cover screws. Install lock washers and screws (2 short screws go next to injector). Tighten screws.

Note. Pressure regulator has a taller regulator "can" than the accumulator assembly.

Place throttle valve in normal closed idle position. Install TPS on rear throttle body with pick-up lever above throttle actuator lever tang. 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 TUNE-UP article.

TORQUE SPECIFICATIONS

TORQUE SPECIFICATIONS

1.8L & 2.5L Fuel Injection Wiring Diagram. Scheme 33

2.0L Fuel Injection Wiring Diagram. Scheme 34