Fuel Pump - Electric Chevrolet Cab & Chassis C20

COMPONENT TESTING

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

DESCRIPTION & OPERATION

All 2.5L engines with throttle body injection (TBI) use a model LN8, low pressure pump with a rated output of 4-13 psi. The LN8 fuel pump is mounted to fuel sending unit in fuel tank.

A power relay is used to control fuel pump operation. When ignition is turned on, relay activates fuel pump for about 2 seconds. This activation is used to prime injectors. If electronic pulses from distributor are not received after the 2 second time period, relay shuts fuel pump off.

Scheme 96

1. Disconnect EFI fuel feed line from throttle body. Route line to a 1 quart, calibrated container. Apply battery voltage to terminal "G" of assembly line communications link (ALCL). (Scheme 96) Fuel pump should supply volume of 1/2 pint or more, within 15 seconds. (Scheme 96): Assembly Line Test Link Test link is under left side of instrument panel.
2. If fuel supply is okay, pump is operating properly. If fuel supply is not okay, check for restriction in supply line. Repair or replace line if necessary. If there are no restrictions, perform «PRESSURE TEST»(/chevrolet/cab-chassis-c20/1985-1986/remont/testing-diagnostics/#fuel-pump-electric__pressure-test) in this article.

PRESSURE TEST

1. Remove air cleaner, and plug thermal vacuum port on throttle body. Remove fuel pump fuse from fuse block in passenger compartment. Start engine. Engine will run until present fuel supply is exhausted. Replace fuse.
2. Remove steel fuel pipe between TBI and fuel filter. Install Pipe and Adaptor Assemblies (J-29658-02) onto Gauge Assembly (J-29658). Install gauge between TBI unit and fuel filter. Start vehicle, and note pressure reading.
3. Reinstall steel fuel line, using new "O" rings if necessary. Start vehicle, check for leaks and turn ignition off. Remove plug covering thermal vacuum port on throttle body. Install air cleaner.
4. Disconnect fuel line at TBI unit. Install low pressure gauge to line. Start engine and note pressure reading. Fuel pump pressure should be 4-6 psi.
5. If pressure reading is correct, pump is okay. If pressure reading is not okay, check for restricted fuel filter, lines and hoses. If all are okay, check power relay.

1. Remove fuel pump fuse from fuse block in passenger compartment. Start engine. Engine will run until present fuel supply is exhausted. Replace fuse. Disconnect battery negative cable. Raise and support vehicle.
2. Remove fuel tank. Turn sending unit lock ring counter-clockwise, and pull lock ring away from tank. Lift fuel lever sending unit and pump assembly from tank. Remove pump from sending unit. To install, reverse removal procedure. Start engine and check for leaks.

SPECIFICATIONS

Note. Specifications not available. Refer to specifications within appropriate TESTING subject in this article.

See also:
• PRESSURE TEST
• TESTING