Engine Controls - Remove/install/overhaul Chevrolet Corvette C4

INTRODUCTION

Removal, overhaul and installation procedures (when given by manufacturer) are covered in this article. If component removal and installation is primarily an unbolt and bolt-on procedure, only a simple tightening specification may be supplied.

ELECTRONIC CONTROL MODULE (ECM)

STATIC CHARGE (VOLTS)

Scheme 1

Note. Before replacing ECM, carefully inspect all wiring and control components. Failure to test for short circuits may result in repeated ECM failure due to grounds and Quad-Driver failure. To prevent internal damage to ECM, ensure ignition is in OFF position when disconnecting or reconnecting ECM connectors or 12-volt components.

Removal

Ensure ignition is in OFF position. Disconnect negative battery cable. Remove electrical connectors from ECM. Remove ECM from vehicle. Remove MEM-CAL or PROM and CALPAC (if equipped) from ECM.

Installation

Install PROM and CALPAC (if equipped) or MEM-CAL in new ECM. Install ECM into vehicle. Connect electrical connectors to ECM. Install access panels. Reconnect negative battery cable to battery.

Removal & Installation

Some ECM models use a CALPAC as well as a PROM. (Scheme 2) If replacing ECM, remove CALPAC from old ECM and install in new ECM. Removal and replacement procedures for CALPAC are same as for PROM. See PROGRAMMABLE READ-ONLY MEMORY (PROM) under IGNITION SYSTEM. If units are improperly installed, grounding diagnostic test lead will set Code 52.

Scheme 2

Disconnect negative battery cable. Remove ECM from vehicle. Using 2 fingers, push retaining clips back from MEM-CAL; at the same time, grasp MEL-CAL at both ends and lift out of socket. DO NOT remove MEM-CAL cover.

1. Carefully align MEM-CAL pins with ECM pin holes. DO NOT press in middle of MEM-CAL. Push downward evenly on ends of MEM-CAL until retaining clips on ends of MEM-CAL snap into place.
2. Install ECM. Reconnect negative battery cable. Turn ignition on and ground ALDL connector. Code 12 should flash at least 4 times (if no other codes are present). If code(s) 42, 43, 51 or 52 is present, or if CHECK ENGINE light stays on constantly with code(s) present, MEM-CAL is not fully seated or is defective. If it is necessary to remove MEM-CAL, follow previous removal instructions.

1. Remove ECM from vehicle. See «ELECTRONIC CONTROL MODULE»(/chevrolet/corvette/c4-1984-1998/remont/removal-installation/#engine-controls-removeinstalloverhaul__electronic-control-module-ecm) under IGNITION SYSTEM. Position ECM so bottom cover faces upward. Remove slide-off PROM access cover by depressing locking tab.
2. Using PROM removal tool, grasp PROM at narrow ends. Gently rock PROM from end to end while pulling up. If installing new PROM, remove old PROM from PROM carrier. (Scheme 2)

Note. Note reference notch locations in PROM, carrier and ECM for reassembly reference.

1. Ensure new PROM has same service number as old one. Place new PROM in PROM carrier. Position PROM carrier squarely over ECM PROM socket. Press on PROM carrier until PROM is firmly seated in ECM. NOTE: Ensure reference notches in both ECM and PROM are properly aligned. If PROM is installed backwards, PROM will be destroyed when ignition is turned on.
2. Install PROM access cover on ECM. Install ECM in vehicle. See «ELECTRONIC CONTROL MODULE (ECM)»(/chevrolet/corvette/c4-1984-1998/remont/removal-installation/#engine-controls-removeinstalloverhaul__electronic-control-module-ecm) under IGNITION SYSTEM. Start engine and ground ALDL diagnostic test connector. Watch for trouble Code 51 or 52.
3. If Code 51 or 52 occurs, PROM is either not fully seated in ECM, installed backwards, has bent pins, or is defective. If bent pins are cracked when trying to straighten, replace PROM. If PROM is installed backwards or is defective, replace PROM.

ELECTRONIC SPARK CONTROL (ESC) MODULE

Note. The ESC is mounted to firewall on a bracket behind the distributor.

Turn ignition off. Remove bracket-to-firewall screws. Rotate bracket to access ESC module. Disconnect ESC module harness connector. Remove ESC mounting screws and remove ESC. To install, reverse removal procedure.

Removal & Installation (2.2L, 2.5L, 3.1L & 3.4L)

1. Disconnect negative battery cable. Unplug connectors at ignition module. Disconnect spark plug wires from coil pack. Remove ignition module from engine block. Remove coils and assembly plate.
2. On 2.5L engines, inspect crankshaft sensor "O" ring for wear, cracks or other damage. Replace as necessary. Lubricate new "O" ring with engine oil before installing.
3. To install, reverse removal procedure. Tighten ignition coil nuts and module to specification. See «TORQUE SPECIFICATIONS»(/chevrolet/corvette/c4-1984-1998/remont/removal-installation/#engine-controls-removeinstalloverhaul__torque-specifications) table at end of article.

Note. If spark plug boots adheres to spark plugs, use Boot Remover (J-36011). Twist first and then pull upward. Boots must be in place on housing before installing ignition system assembly, or damage may result.

Scheme 3

Removal & Installation (2.3L)

1. Disconnect negative battery cable. Disconnect 11-pin harness connector. Remove 4 ignition module cover-to-cam carrier bolts.
2. Remove ignition system assembly from engine. Remove 4 housing cover screws. Remove housing cover. Remove coil harness connector from module. Remove module-to-cover screws. Remove module from cover. To install, reverse removal procedure.

Note. DO NOT wipe grease from module or coil if module is not being replaced. If installing a new module, spread silicone grease on metal face of module and on cover where module seats. Grease is included with new module and is necessary for module cooling purposes.

Removal & Installation (3.3L & 3.8L)

Disconnect negative battery cable. Unplug 14-way connector at ignition module. Disconnect spark plug wires from coil pack. Remove nuts and washers securing ignition module to bracket. Remove coil-to-ignition module Torx screws. Note wire colors for reassembly. Unplug connectors between ignition coil and module. Remove module. To install, reverse removal procedure.

Removal (3.3L & 3.8L)

1. Remove serpentine belt from crankshaft pulley. Raise vehicle on hoist. Remove right front tire and wheel assembly. Remove right inner fender access cover.
2. Using 28-mm socket, remove crankshaft harmonic balancer retaining bolt. Remove harmonic balancer. Remove foreign object deflector ( DO NOT use pry bar). Disconnect sensor harness connector. Remove sensor and pedestal (as an assembly) from block. Remove sensor from pedestal.

1. Loosely install sensor on pedestal. Position sensor, with pedestal attached, onto Installer (J-37089). (Scheme 4) Position installer onto crankshaft.
2. Install pedestal-to-block bolts. Tighten bolts to 18-26 ft. lbs. (25-35 N.m). Tighten pedestal pinch bolt to 26-44 INCH lbs. (3-5 N.m). Remove installer. Install foreign object deflector. Place harmonic balancer onto installer. Rotate balancer on installer. If any vanes of interrupter rings contact installer, replace harmonic balancer.
3. Install balancer on crankshaft. To complete installation, reverse removal procedure. Tighten balancer retaining bolt to specification. See «TORQUE SPECIFICATIONS»(/chevrolet/corvette/c4-1984-1998/remont/removal-installation/#engine-controls-removeinstalloverhaul__torque-specifications) table at end of article.

Scheme 4

Disconnect negative battery cable. Remove camshaft sensor attaching bolt. Disconnect wiring harness and remove sensor. To install, reverse removal procedure.

Removal & Installation (2.2L, 2.3L, 3.1L & 3.4L)

Disconnect sensor harness at IDI or DIS ignition module. Remove bolt and sensor from engine block. Inspect crankshaft sensor "O" ring for wear, cracks or other damage. Replace as necessary. Lubricate new "O" rings with engine oil before installing. To install, reverse removal procedure.

Removal & Installation (2.5L)

Remove DIS ignition module. Remove crankshaft sensor mounting screws and remove sensor from DIS module. Inspect "O" ring for wear before installing DIS module. Replace as necessary. To install, reverse removal procedure. Tighten screws to specification. See TORQUE SPECIFICATIONS table at end of article.

Removal & Installation (3.3L)

Disconnect negative battery cable. Remove spark plug wires from coil. Remove coil-to-module bolts. Remove coil assembly. To install, reverse removal procedure. Tighten retaining bolts to specification. See TORQUE SPECIFICATIONS table at end of article.

Removal & Installation (3.8L)

Disconnect negative battery cable. Remove spark plug wires from coil pack. Remove coil-to-ignition module Torx screws. Tilt coil assembly back. Disconnect module connectors and remove coil pack. To install, reverse removal procedure. Tighten retaining bolts to specifications. See TORQUE SPECIFICATIONS table at end of article.

Disconnect negative battery cable. Remove spark plug wires from coils. Remove nuts or screws from ignition coils. Remove coils. To install, reverse removal procedure.

1)Disconnect negative battery cable. Disconnect 11-pin harness connector. Remove ignition cover-to-cam carrier bolts. Remove ignition system assembly from engine. Remove housing cover screws. Remove housing cover.

2) Remove coil harness connector from module. Remove module-to-cover screws. Remove module from cover. To install, reverse removal procedures. Tighten screws to specification. See TORQUE SPECIFICATIONS table at end of article.

FUEL PRESSURE RELIEF (PFI)

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

1. Relieve fuel pressure. See «FUEL PRESSURE RELIEF (PFI)»(/chevrolet/corvette/c4-1984-1998/remont/removal-installation/#engine-controls-removeinstalloverhaul__fuel-pressure-relief-pfi) under FUEL SYSTEM (PFI). Remove air inlet ducts. Disconnect and mark electrical connections and vacuum hoses from throttle body. Disconnect control cables from throttle body.
2. Drain cooling system. Remove coolant hoses. Remove throttle body retaining bolts. Remove throttle body and gasket.

Note. Identification number is stamped on throttle body. Use identification number to order replacement components.

1. To install, reverse removal procedure; use new gasket. Tighten retaining bolts to specification. See «TORQUE SPECIFICATIONS»(/chevrolet/corvette/c4-1984-1998/remont/removal-installation/#engine-controls-removeinstalloverhaul__torque-specifications) table at end of article. Refill cooling system.
2. If installing new Idle Air Control (IAC), ensure IAC pintle length setting before installing. See IDLE AIR CONTROL VALVE under «FUEL SYSTEM (PFI)»(/chevrolet/corvette/c4-1984-1998/remont/removal-installation/#engine-controls-removeinstalloverhaul) . Adjust idle speed and TPS (if removed). See procedures in ADJUSTMENTS article.

Removal (2.3L, 3.3L, 3.8L & 4.9L)

1. Relieve fuel pressure. See «FUEL PRESSURE RELIEF (PFI)»(/chevrolet/corvette/c4-1984-1998/remont/removal-installation/#engine-controls-removeinstalloverhaul__fuel-pressure-relief-pfi) under FUEL SYSTEM (PFI). Disconnect pressure regulator-to-fuel rail hose. On 2.3L, remove fuel rail. See «FUEL RAIL & INJECTORS»(/chevrolet/corvette/c4-1984-1998/remont/removal-installation/#engine-controls-removeinstalloverhaul__fuel-rail-injectors) under FUEL SYSTEM (PFI).
2. On all models, remove pressure regulator retaining bolts. Remove pressure regulator from fuel rail. On 2.3L, remove pressure regulator retainer and seal from fuel rail.

To install, reverse removal procedures. Always replace "O" rings. Lubricate fuel rail seal with oil and install in regulator. Tighten bolts to specification. See TORQUE SPECIFICATIONS table at end of article.

Removal (3.1L & 3.4L)

1. Relieve fuel pressure. See «FUEL PRESSURE RELIEF (PFI)»(/chevrolet/corvette/c4-1984-1998/remont/removal-installation/#engine-controls-removeinstalloverhaul__fuel-pressure-relief-pfi) under FUEL SYSTEM (PFI). Remove upper manifold or intake manifold plenum. On 3.1L models, remove fuel rails. See «FUEL RAIL & INJECTORS»(/chevrolet/corvette/c4-1984-1998/remont/removal-installation/#engine-controls-removeinstalloverhaul__fuel-rail-injectors) under FUEL SYSTEM (PFI).
2. On all models, remove inlet and return fuel fittings and gaskets. Remove pressure regulator-to-bracket retaining bolts. Separate pressure regulator from fuel rail.
3. Remove pressure regulator base-to-fuel rail connector tubes from pressure regulator.

1. To install, reverse removal procedures. Lubricate new "O" rings with oil. Install fuel return "O" rings on fuel rails. Return "O" rings are larger in diameter than connector tube "O" rings.
2. Tighten bolts to specification. See «TORQUE SPECIFICATIONS»(/chevrolet/corvette/c4-1984-1998/remont/removal-installation/#engine-controls-removeinstalloverhaul__torque-specifications) table at end of article.

Removal (5.0L & 5.7L)

1. Relieve fuel pressure, and remove fuel rails. Refer to «FUEL PRESSURE RELIEF (PFI)»(/chevrolet/corvette/c4-1984-1998/remont/removal-installation/#engine-controls-removeinstalloverhaul__fuel-pressure-relief-pfi) and «FUEL RAIL & INJECTORS»(/chevrolet/corvette/c4-1984-1998/remont/removal-installation/#engine-controls-removeinstalloverhaul__fuel-rail-injectors) under FUEL SYSTEM (PFI).
2. Remove front crossover tube retainer on right fuel rail. Remove rear crossover tube retainer at pressure regulator on right fuel rail. Separate fuel rail assemblies.
3. Remove pressure regulator bracket-to-fuel rail bolt. Remove bracket-to-regulator base bolt. Remove bracket. Remove fuel outlet tube-to-right fuel rail bolt. Remove base-to-right fuel rail bolt.
4. Remove pressure regulator assembly from fuel rail. Rotate pressure regulator and remove from outlet tube. Remove base-to-fuel rail connector tube. Remove "O" rings from connector tube, outlet tube and crossover tubes.

To install, reverse removal procedures. Install new "O" rings and lubricate with oil. Tighten retaining bolts to specification. See TORQUE SPECIFICATIONS table at end of article.

FUEL RAIL & INJECTORS

1. Relieve fuel pressure. See «FUEL PRESSURE RELIEF (PFI)»(/chevrolet/corvette/c4-1984-1998/remont/removal-installation/#engine-controls-removeinstalloverhaul__fuel-pressure-relief-pfi) under FUEL SYSTEM (PFI). Turn ignition off. Disconnect wiring connectors from injectors. Disconnect and plug hoses to fuel rail.
2. Remove fuel rail retaining bolts. Remove injector-to-fuel rail retaining clip (if used). Separate fuel rail from injectors. Remove injectors. (Scheme 5)

Scheme 5

Scheme 6

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

To install, reverse removal procedure. Coat new "O" rings with oil. Install "O" rings on injectors. Tighten fuel rail retaining bolts to specification. See TORQUE SPECIFICATIONS table at end of article.

Removal (2.3L)

1. Relieve fuel pressure. See «FUEL PRESSURE RELIEF (PFI)»(/chevrolet/corvette/c4-1984-1998/remont/removal-installation/#engine-controls-removeinstalloverhaul__fuel-pressure-relief-pfi) under FUEL SYSTEM (PFI). Remove crankcase ventilation oil/separator.
2. Remove fuel lines from fuel rail. Remove vacuum line at pressure regulator. Disconnect wiring connector while pushing inward on connector. Remove fuel rail retaining bolts. Remove fuel rail. (Scheme 7)
3. Remove injector-to-fuel rail retaining clip. Remove injector from fuel rail. Remove injector "O" rings.

Scheme 7

To install reverse removal procedure. Lubricate injector "O" rings with oil. Install injector-to-fuel rail retaining clip, with open end facing injector electrical connection. Tighten fuel rail retaining bolts.

Scheme 8

1. Relieve fuel pressure. See «FUEL PRESSURE RELIEF (PFI)»(/chevrolet/corvette/c4-1984-1998/remont/removal-installation/#engine-controls-removeinstalloverhaul__fuel-pressure-relief-pfi) under FUEL SYSTEM (PFI). Disconnect negative battery cable. Remove intake manifold upper plenum. Disconnect and mark vacuum lines. Remove EGR-to-intake manifold retaining bolts. Some models use an EGR pipe which requires removal at EGR base.
2. Remove throttle cable bracket bolts. Disconnect cables and electrical wiring connections from throttle body. Remove throttle body from intake manifold. Remove plenum and gasket. (Scheme 8)
3. Disconnect vacuum hose to pressure regulator. Remove runners. Disconnect fuel lines from fuel rail. With ignition off, disconnect electrical connections from injectors.
4. Remove fuel rail retaining bolts. Remove fuel rail and injectors. On 5.0L and 5.7L, rotate injector retaining clip to unlock position. On all models, remove injectors from fuel rail. Remove "O" rings from injectors.

To install, reverse removal procedure. Coat new "O" rings with oil. Install "O" rings on injectors. Tighten bolts to specification. See TORQUE SPECIFICATIONS table at end of article.

Removal (4.9L)

1. Remove air cleaner. Relieve fuel pressure. Refer to «FUEL PRESSURE RELIEF (PFI)»(/chevrolet/corvette/c4-1984-1998/remont/removal-installation/#engine-controls-removeinstalloverhaul__fuel-pressure-relief-pfi) under FUEL SYSTEM (PFI). Disconnect negative battery cable. Remove power steering pump and set aside.
2. Disconnect vacuum hose to pressure regulator and base assembly. Disconnect accelerator cable, cruise control cable and bracket. Disconnect electrical connectors. Drain coolant and disconnect coolant hose to thermostat housing.
3. Wrap a shop towel around fuel line. Disconnect fuel feed line from rear fuel rail assembly and fuel return line. Discard "O" rings. Disconnect EGR vacuum hose. Remove the EGR valve. Remove fuel rail attaching bolts. Disconnect electrical connectors at front and rear fuel rail assemblies. Remove fuel rail from the intake manifold. (Scheme 6)

To install, reverse removal procedure. Coat new "O" rings with oil. Install "O" rings on injectors. Tighten bolts to specification. See TORQUE SPECIFICATIONS table at end of article.

Remove air cleaner. Disconnect electrical connector. Remove retaining screws and Idle Speed Control (ISC) motor. To install, reverse removal procedure. To adjust ISC minimum and maximum authority, see appropriate ADJUSTMENTS article in this section.

Note. The ISC motor is factory calibrated and should not be disassembled. Replace motor as a complete assembly only. DO NOT soak ISC motor in carburetor cleaner.

IDLE AIR CONTROL (IAC) VALVE

Remove electrical connector from IAC valve. Remove IAC valve and gasket or "O" ring. IAC valve screws into housing on 5.0L and 5.7L engines. Retaining screws are used on 2.3L, 3.1L, 3.3L, 3.4L and 3.8L engines.

1. Check the extended distance of new IAC before installing. Damage will occur if measurement is incorrect. Distance must not exceed 1 1/8" (28 mm). Measurement should be taken from valve housing flange to end of cone. DO NOT extend or retract pintle on IAC valve that has been in service, or damage to internal worm drive may occur.
2. To retract pintle on new IAC, slowly exert finger pressure on valve. Install new "O" ring or gasket on valve. Coat "O" ring with oil. Install IAC valve. Tighten IAC valve to specifications. See «TORQUE SPECIFICATIONS»(/chevrolet/corvette/c4-1984-1998/remont/removal-installation/#engine-controls-removeinstalloverhaul__torque-specifications) table at end of article. Install electrical connector.
3. To reset IAC valve on 2.3L (VIN A), connect "Scan" tester. Start engine and hold engine speed at about 2000 RPM. Using "Scan" tester, select Field Service mode for 10 seconds then exit from Field Service mode. Turn engine off, then restart engine and check for proper idle operation.
4. On 2.3L (VIN D), turn ignition on, but do not start engine. Ground ALDL connector for 5 seconds. Remove ground from ALDL connector. Turn ignition on for 10 seconds. Start engine and check for proper idle operation.
5. On 3.1L & 3.4L, turn ignition on for 5 seconds, then turn ignition off for 10 seconds. Start engine and check for proper idle operation.
6. On 3.3L, turn ignition on, but do not start engine. Ground ALDL connector for 5 seconds. Remove ground from ALDL connector. Start engine and check for proper idle operation.
7. On 5.7L (VIN 8), depress accelerator slightly. Start and run engine for 5 seconds. Turn ignition off for 10 seconds. Restart engine and check for proper idle operation.

Removal (Camaro & Firebird)

1. Relieve fuel system pressure. Disconnect battery negative terminal. Raise car on hoist. Drain fuel from fuel tank. Disconnect exhaust pipe at converter and rear hanger. Allow exhaust to hang over axle assembly.
2. Remove tailpipe and muffler heat shields. Remove fuel filler neck shield behind left rear tire. Remove rear suspension track bar and brace. Disconnect harness connector to fuel pump assembly.
3. Disconnect all fuel lines. Remove fuel line retaining bracket on left side and remove brake line clip from bracket.
4. Position support jack under axle assembly. Disconnect lower ends of shock absorbers. Disconnect rear stabilizer bar from frame (if equipped).
5. On models equipped with 2-piece driveshaft, remove center support bearing-to-rear axle torque arm bolts. On all models, remove rear axle torque arm-to-differential housing bolts/nuts. Wire end of rear axle torque arm aside. Remove driveshaft-to-differential yoke bolts/screws. Wire end of driveshaft aside.
6. Lower rear suspension as far as possible without damaging brake lines and cables and remove both coil springs. Remove tank straps bolts. Remove fuel tank by rotating front of tank down and sliding to the right. Remove fuel pump assembly from fuel tank.

Removal (Corvette)

1. Relieve fuel system pressure. Remove fuse marked "Fuel Pump" from fuse block in passenger compartment. Crank engine. Engine will start and run until fuel in line is exhausted. When engine stops, engage starter again for 3 seconds to ensure engine will not start.
2. Remove battery ground cable. Remove fuel cap, fuel tank filler door. Remove filler neck housing and disconnect drain hose. Remove screws attaching fuel meter and pump assembly to tank. Disconnect fuel hoses, vapor hose and electrical connector from fuel meter and pump assembly. Pull pump up into pulsator while pulling outward away from bottom support. Remove pump.

Removal (Except Camaro, Corvette & Firebird)

1. Disconnect negative battery cable. Relieve fuel pressure. See «FUEL PRESSURE RELIEF (PFI)»(/chevrolet/corvette/c4-1984-1998/remont/removal-installation/#engine-controls-removeinstalloverhaul__fuel-pressure-relief-pfi) under FUEL SYSTEM (PFI). Remove filler neck. Lower fuel tank. Disconnect fuel lines and electrical connection.
2. Remove fuel level sending unit and fuel pump retaining bolts or cam lock ring. Lift assembly from fuel tank and remove fuel pump from sending unit.
3. Pull fuel pump upward while pulling outward away from bottom support. Use care not to damage rubber insulator and strainer.

Reverse removal procedure, using new "O" ring/gasket. Tighten fasteners to specification. See TORQUE SPECIFICATIONS .

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

1. With throttle valve in closed position, install TPS on throttle body. Ensure TPS lever engages with drive lever on throttle shaft. Install retaining screws and electrical connection.
2. The TPS on most models are self-zeroing and are not adjustable. On these models, if voltage is less than 1.25 volts, the TPS does not need to be serviced. On models with adjustable TPS, adjust TPS to specification and tighten retaining screws. Refer to appropriate ADJUSTMENTS article in this section.

OXYGEN (O2) SENSOR

O2 sensor is mounted in the exhaust pipe, below exhaust manifold. It is equipped with a permanent pigtail which must be protected when removing sensor.

1. Ensure sensor is free of contaminants; avoid using cleaning solvents of any type. Sensor may be difficult to remove when engine temperature is less than 120°F (48°C). Excessive removal force may damage threads in exhaust manifold or pipe.
2. Disconnect negative battery cable at battery. Disconnect electrical connector from oxygen sensor. Carefully remove oxygen sensor from exhaust pipe.

1. Whenever an oxygen sensor is removed, threads must be coated with anti-seize compound before it is reinstalled. New oxygen sensors already have this compound applied to threads.
2. Install oxygen sensor in exhaust pipe, and tighten sensor to 30 ft. lbs. (41 N.m). Reconnect electrical connector to oxygen sensor. Reconnect negative battery cable.

FUEL PRESSURE RELIEF (TBI)

Disconnect negative battery cable. Remove fuel filler cap. Since these TBI units contain an internal bleed-down feature, system fuel pressure should dissipate after a short time.

THROTTLE BODY

An 8-digit unit identification number is stamped on throttle body assembly. On model 220, number is stamped vertically on front of throttle body, at Throttle Position Sensor (TPS) side. On model 700, number can be found on fuel meter body assembly, below pressure regulator. Letter codes are stamped on throttle body, at external tube locations, to identify vacuum hose connections.

Note. Ensure residual fuel pressure is relieved before working on throttle body.

1. Relieve fuel pressure. See «FUEL PRESSURE RELIEF (TBI)»(/chevrolet/corvette/c4-1984-1998/remont/removal-installation/#engine-controls-removeinstalloverhaul__fuel-pressure-relief-tbi) under FUEL SYSTEM (TBI). Disconnect negative battery cable. Remove air cleaner and related ducting.
2. Remove electrical connectors from Idle Air Control (IAC), TPS and fuel injector(s). Lay wiring harness aside. Remove throttle cable, return springs, transmission/transaxle cable, and cruise control cable (if equipped). Label and remove vacuum hoses.
3. Remove fuel feed and return lines. Use 2 wrenches to prevent nuts in throttle body from coming loose. Remove fuel line "O" rings and discard. Remove throttle body retaining bolts. Remove TBI unit and base gasket. Discard base gasket.

Disassembly (Throttle Body Cover Model 220)

1. Place throttle body on Holding Fixture (J-9789-118 or BT 30-15) to prevent damage to throttle valve. Remove cover-to-throttle body screws; note location of 2 short screws.
2. Remove throttle body cover. (Scheme 10) Throttle body cover and pressure regulator are serviced as an assembly. DO NOT remove pressure regulator-to-cover screws. Remove TPS and IAC assembly. Throttle valve screws are staked in position and should not be removed.

Disassembly (Fuel Meter Assembly Model 700)

Remove fuel meter-to-throttle body retaining screws. Remove fuel meter assembly. (Scheme 9) Discard gasket. If fuel pressure regulator cover is removed, replace regulator diaphragm to prevent fuel leaks. Remove TPS and IAC assembly. Throttle valve screws are staked in position and should not be removed.

Scheme 9

Scheme 10

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 the following in cleaner solvent: TPS, IAC, throttle body cover, fuel meter and pressure regulator assemblies, fuel injector, fuel filter, rubber parts and diaphragms.
3. Inspect mating surfaces for damage that may prevent gasket sealing. Repair or replace components as necessary.

Reassembly (Throttle Body Cover Model 220)

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; ensure pressure regulator dust seal and cover gaskets are in place.
2. Apply thread locking compound to cover attaching screws. Install cover screws and lock washers. Tighten screws. Connect electrical lead to fuel injector and install air cleaner. To complete assembly, reverse disassembly procedure.

Reassembly (Fuel Meter Assembly Model 700)

1. Install new fuel meter-to-throttle body assembly gasket. Match cutout 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 specification. See «TORQUE SPECIFICATIONS»(/chevrolet/corvette/c4-1984-1998/remont/removal-installation/#engine-controls-removeinstalloverhaul__torque-specifications) table at end of article.
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.

1. Install throttle body unit to intake manifold; use new gaskets. Tighten retaining bolts to specification. See «TORQUE SPECIFICATIONS»(/chevrolet/corvette/c4-1984-1998/remont/removal-installation/#engine-controls-removeinstalloverhaul__torque-specifications) table at end of article. Install new "O" rings onto fuel lines.
2. Connect fuel feed and return lines throttle body. Use a back-up wrench to prevent fuel line fittings in throttle body from turning. Tighten fuel line nuts to specifications. See «TORQUE SPECIFICATIONS»(/chevrolet/corvette/c4-1984-1998/remont/removal-installation/#engine-controls-removeinstalloverhaul__torque-specifications) table at end of article.

Removal (Model 220)

1. Relieve fuel pressure. See «FUEL PRESSURE RELIEF (TBI)»(/chevrolet/corvette/c4-1984-1998/remont/removal-installation/#engine-controls-removeinstalloverhaul__fuel-pressure-relief-tbi) under FUEL SYSTEM (TBI). Remove throttle body cover, leaving cover gasket in place. Using screwdriver and fulcrum, carefully pry injector out. (Scheme 11) Remove small "O" ring from nozzle end of injector.
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.

1. Install fuel filter on nozzle end of fuel injector. Ensure large end of filter faces injector so filter covers the 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 10) Ensure "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 will cause fuel 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 fully seated. Electrical terminals of injector will be approximately parallel with throttle shaft. Install throttle body cover.

Removal (Model 700)

Relieve fuel pressure. See FUEL PRESSURE RELIEF (TBI) under FUEL SYSTEM (TBI). Remove fuel injector retainer screw and remove 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 assembly, with electrical connector facing cutout 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 related ducting. Remove Idle Air Control (IAC) electrical connector. On model 220, unscrew IAC valve. On model 700, 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, valve will be damaged during installation.
2. To set IAC pintle length on new IAC, use finger pressure to slowly retract pintle. Lubricate new "O" ring with ATF and install new gasket. Install IAC valve on throttle body. Tighten IAC valve to specification. See «TORQUE SPECIFICATIONS»(/chevrolet/corvette/c4-1984-1998/remont/removal-installation/#engine-controls-removeinstalloverhaul__torque-specifications) table at end of article. 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 hold engine speed at greater than 2000 RPM. Ground ALDL connector for 10 seconds then remove ground. Turn ignition off then restart engine. Check for proper idle operation.

Removal & Installation (Except Corvette)

1. Disconnect negative battery cable. Relieve fuel pressure. See «FUEL PRESSURE RELIEF (TBI)»(/chevrolet/corvette/c4-1984-1998/remont/removal-installation/#engine-controls-removeinstalloverhaul__fuel-pressure-relief-tbi) under FUEL SYSTEM (TBI). Remove filler neck. Lower fuel tank. Disconnect fuel lines and electrical connection.
2. Remove fuel level sending unit and fuel pump retaining bolts or cam lock ring. Lift assembly from fuel tank and remove fuel pump from sending unit.
3. Pull fuel pump upward while pulling outward away from bottom support. Use care not to damage rubber insulator and strainer. To install, reverse removal procedure; use new "O" ring and gasket.

1. Relieve fuel system pressure. Remove fuse marked "Fuel Pump" from fuse block in passenger compartment. Crank engine. Engine will start and run until fuel in line is exhausted. When engine stops, engage starter again for 3 seconds to ensure engine will not start.
2. Remove battery ground cable. Remove fuel cap, fuel tank filler door. Remove filler neck housing and disconnect drain hose. Remove screws attaching fuel meter and pump assembly to tank. Disconnect fuel hoses, vapor hose and electrical connector from fuel meter and pump assembly. Pull pump up into pulsator while pulling outward away from bottom support. Remove pump.

Reverse removal procedure, using new gasket.

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

1. With throttle valve in closed position, install TPS on throttle body. Ensure TPS lever engages with drive lever on throttle shaft. Install retaining screws and electrical connection.
2. The TPS on most models are self-zeroing and are not adjustable. On these models, if voltage reading is less than 1.25 volts, TPS does not need to be serviced. On models with adjustable TPS, adjust TPS to specification and tighten retaining screws. Refer to ADJUSTMENTS article.

O2 sensor is mounted in the exhaust pipe, below exhaust manifold. It is equipped with a permanent pigtail which must be protected when removing sensor.

1. Ensure sensor is free of contaminants; avoid using cleaning solvents of any type. Sensor may be difficult to remove when engine temperature is less than 120°F (48°C). Excessive removal force may damage threads in exhaust manifold or pipe.
2. Disconnect negative battery cable at battery. Disconnect electrical connector from oxygen sensor. Carefully remove oxygen sensor from exhaust pipe.

1. Whenever an oxygen sensor is removed, threads must be coated with anti-seize compound before it is reinstalled. New oxygen sensors already have this compound applied to threads.
2. Install oxygen sensor in exhaust pipe, and tighten sensor to 30 ft. lbs. (41 N.m). Reconnect electrical connector to oxygen sensor. Reconnect negative battery cable.

TORQUE SPECIFICATIONS

TORQUE SPECIFICATIONS

See also:
• PROGRAMMABLE READ-ONLY MEMORY (PROM)
• ELECTRONIC CONTROL MODULE
• TORQUE SPECIFICATIONS
• FUEL PRESSURE RELIEF (PFI)
• FUEL RAIL & INJECTORS
• FUEL PRESSURE RELIEF (TBI)