Engine Controls - Remove/install/overhaul - 7.4L: Removal & Installation Chevrolet Suburban C2500

Removal

Disconnect negative battery cable. Unplug electrical connectors from PCM. see scheme 1 Remove PCM from vehicle. Remove PROM or MEM-CAL from PCM. See MEM-CAL or PROGRAMMABLE READ-ONLY MEMORY (PROM).

Installation

Install PROM or MEM-CAL in NEW PCM. See MEM-CAL or PROGRAMMABLE READ-ONLY MEMORY (PROM). Install PCM into vehicle. Connect electrical connectors to PCM. Install access panels. Reconnect negative battery cable.

Disconnect negative battery cable. Remove PCM from vehicle. See REMOVAL under CONTROL MODULE . Using 2 fingers, push retaining clips back from MEM-CAL. At the same time, grasp it at both ends and lift out of socket. DO NOT remove MEM-CAL cover.

1. Carefully align MEM-CAL pins with PCM 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 PCM. Reconnect negative battery cable. Turn ignition on and ground DLC terminal "B". DTC 12 should be flashed at least 4 times. If DTC 12 is not flashed at least 4 times, other codes are present. If DTC 51 is present, or if MIL stays on constantly with code(s) present, MEM-CAL is not fully seated, or is defective.

1. Remove PCM from vehicle. See REMOVAL under «CONTROL MODULE»(ref-20115-S04816628902001010200000) . Position PCM so bottom cover is facing 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.

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

1. Ensure new PROM has same service number as old one or correct factory upgrade. Place NEW PROM in PROM carrier, and position squarely over PCM PROM socket. Press on PROM carrier until PROM is firmly seated in PCM. NOTE: Ensure reference notches in PCM and PROM are properly aligned. If PROM is installed backwards and ignition is turned on, PROM will be destroyed.
2. Install PROM access cover on PCM. Install PCM in vehicle. See INSTALLATION under «CONTROL MODULE»(ref-20115-S04816628902001010200000) . Turn ignition on and ground DLC terminal "B". Check for DTC 51.
3. If DTC 51 is present, PROM is not fully seated in PCM, installed backwards, has bent pins, or is defective. If bent pins are cracked while straightening, replace PROM. If PROM is installed backwards or is defective, replace PROM.

Scheme 16

1. Relieve fuel pressure. Refer to «FUEL SYSTEM PRESSURE RELIEF (TBI)»(ref-20115-S00889888772001010200000) .
2. Remove fuel filler cap.
3. Remove fuel feed lines.
4. Remove clamp bolt.
5. Remove Filter and clamp.
6. Remove clamp from filter.

1. Install clamp to filter.
2. Install clamp bolt.
3. Install fuel feed nuts.
4. Install fuel filler cap.
5. Check for leaks.

Removal & Installation

1. Relieve fuel system pressure. See FUEL SYSTEM PRESSURE RELIEF (TBI) under «FUEL SYSTEM»(ref-20115-S13329591102001010200000) . Disconnect negative battery cable. Raise vehicle and remove fuel tank. Remove sender unit and pump by turning cam lock counterclockwise using Tool (J-36608 or J-24187).
2. Remove fuel pump from sending unit by pulling pump up into attaching hose while pulling outward from the bottom support. DO NOT damage rubber insulator or strainer. To install, reverse removal procedure.

Removal (TBI)

Remove air cleaner and related ducting. Disconnect Idle Air Control (IAC) electrical connector. Unscrew IAC valve. Replace if necessary.

1. Inspect gasket for damage. Replace if necessary. Measure distance between tip of IAC valve pintle and mounting flange. Distance should not exceed 1 1/8" (28 mm). If valve is extended too far, damage to valve will result during installation.
2. To set IAC valve pintle length on new IAC valve, use finger pressure to slowly retract pintle. Install NEW gasket. Install IAC valve on throttle body. Tighten IAC valve to specification. See «TORQUE SPECIFICATIONS»(ref-20115-S16134245232001010200000) . CAUTION: DO NOT manually extend or retract pintle if IAC valve has been in service, or damage to worm gear will result.
3. Connect IAC valve harness connector and install air cleaner. Start engine and allow it to reach normal operating temperature. Drive vehicle. It may be necessary to reset idle speed. To reset, disconnect negative battery cable for 10 seconds and reconnect. Cycle ignition on with engine off for 5 seconds. Turn ignition off for 10 seconds and restart vehicle. Proper idle will be initialized.

1. Remove air cleaner, adapter and gasket. Relieve fuel pressure. See «FUEL SYSTEM PRESSURE RELIEF (TBI)»(ref-20115-S00889888772001010200000) under FUEL SYSTEM.
2. Disconnect electrical harness connectors from IAC valve, TP sensor and fuel injectors. Disconnect fuel lines from throttle body. Discard fuel line "O" rings. Disconnect grommet with wires from throttle body.
3. Disconnect throttle linkage, return spring and cruise control linkage (if equipped). Label and disconnect all vacuum hoses from throttle body. Remove throttle body mounting bolts/nut. Remove throttle body.

Note. Disassembling throttle body unit for immersion in cleaning solvent requires removal of fuel meter assembly, TP sensor, IAC valve and governor assembly (if equipped). Throttle valve screws are staked in position and should NOT be removed.

To install, reverse removal procedure. Ensure throttle body and intake manifold sealing surfaces are clean. Use NEW throttle body gasket and fuel line "O" rings. Check fuel system for leaks by turning ignition on, but DO NOT start engine.

Scheme 17

1. Relieve fuel pressure. See FUEL SYSTEM PRESSURE RELIEF (TBI) under «FUEL SYSTEM»(ref-20115-S13329591102001010200000). Disconnect fuel injector electrical connector. Remove fuel meter cover assembly (TBI 220, or fuel meter body cover (TBI 295), leaving cover gasket in place. Using screwdriver and fulcrum, pry injector out. (Scheme 18) 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 fuel meter cover gasket. Remove large "O" ring and steel back-up washer (if equipped) 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 raised rib at base of injector. Lubricate small "O" ring with Automatic Transmission Fluid (ATF), and push "O" ring on nozzle end of injector until it presses against injector filter.
2. Install steel back-up washer (if equipped) in top counterbore of throttle body injector cavity. Lubricate large "O" ring with ATF, and install "O" ring directly over back-up washer. Ensure "O" ring is seated properly in cavity, and is flush with top of throttle body casting. CAUTION: Install back-up washer and large "O" ring before installing 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. Install fuel meter cover.

Scheme 18

1. Remove air cleaner assembly, extension (spacer) and gasket. Disconnect electrical harness connector from governor assembly. Rotate the throttle cam lever to 11 o'clock position. Install a 14 mm socket between governor drive motor and throttle cam lever to block throttle cam lever. see scheme 6
2. Remove mounting screws. Hold throttle valve closed. Remove governor assembly. see scheme 6
3. To install, make sure throttle cam lever is blocked open (11 o'clock position). Install governor assembly. see scheme 6 Remove 14 mm socket. Ensure throttle cam lever and throttle valves rotate freely. To complete installation, install remaining parts.

1. Disconnect negative battery cable. On TBI models, remove air cleaner assembly. Remove upper intake manifold assembly.
2. On all models, disconnect electrical connectors to distributor. Remove distributor cap and move aside. Remove distributor hold-down bolt and hold-down clamp. Note position of rotor. Pull up slightly on distributor until rotor stops turning counterclockwise and again note position of rotor. Remove distributor from engine.

1. To install, reverse removal procedure. To ensure correct timing of distributor, install with rotor correctly positioned as it was before distributor was removed.
2. If engine was cranked after distributor was removed, remove No. 1 spark plug. Place finger over No. 1 cylinder spark plug hole. Crank engine slowly until compression is felt. Align timing mark on pulley to "0" on engine timing indicator. Turn rotor to point to cylinder No. 1 spark plug tower on distributor cap. Complete distributor installation. Start engine and check ignition timing.

1. Remove air cleaner assembly. Disconnect electrical connector from TP sensor. Remove attaching screws, lock washers, retainers, and TP sensor.
2. To install, reverse removal procedure. Adjust TP sensor to specification. See ADJUSTMENTS article in the ENGINE PERFORMANCE section. When replacing a TP sensor, ensure correct part number is used. Use Loctite on TP sensor attaching screws.

1. Oxygen sensor is mounted in the exhaust pipe, below exhaust manifold. Ensure sensor is free of contaminants. DO NOT use 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. Disconnect electrical connector from oxygen sensor. Carefully remove oxygen sensor from exhaust pipe.

1. Whenever oxygen sensor is removed, coat threads with anti-seize compound before reinstalling. 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.