Fuel Pump - Electric GMC Pickup R2500

DESCRIPTION & OPERATION

Throttle Body Injection (TBI) models use low pressure pump with an output of 4-13 psi (.28-.91 kg/cm 2 ). Pump is mounted to sending unit in fuel tank. A relay is used to control fuel pump operation. When ignition is turned on, relay activates fuel pump for 2 seconds to prime injectors. If electronic pulses from distributor are not received after 2 second time period, relay shuts fuel pump off.

For additional information on operation and testing of fuel system, see COMPUTERIZED ENGINE CONTROLS section.

Scheme 48

1. Relieve fuel system pressure by removing "FUEL PUMP" fuse. Crank engine. Engine will start and run until fuel in lines is used. After engine stops, crank engine an additional 3 seconds to relieve remaining pressure. Turn ignition off and install fuel pump fuse.
2. Connect fuel hose to throttle body feed line. Route line to one quart, calibrated container. Apply battery voltage to terminal "G" of Assembly Line Diagnostic Link (ALDL) connector. (Scheme 48) Fuel pump should supply 1/2 pint (240 ml) or more in 15 seconds. (Scheme 48): Assembly Line Diagnostic Link ALDL connector is under left side of instrument panel.
3. If fuel supply is within specifications, pump is operating properly. If fuel supply is less than specifications, check for restrictions in supply line. Repair or replace line if necessary. If there are no restrictions, perform FUEL PUMP PRESSURE TEST.

FUEL PUMP PRESSURE TEST

1. Relieve fuel system pressure by removing "FUEL PUMP" fuse from fuse block. Crank engine. Engine will start and run until fuel in lines is used. After engine stops, crank engine an additional 3 seconds to relieve remaining pressure. Turn ignition off and install fuel pump fuse.
2. Remove air cleaner. Plug thermal vacuum port on throttle body. Install Fuel Pressure Gauge (J-29548-A) between throttle body and fuel filter. Start vehicle, and note pressure reading. Pressure should be 9-13 psi (.63-.91 kg/cm 2 ).
3. If pressure exceeds specifications, inspect throttle body injection system. Relieve fuel pressure. Remove gauge and connect fuel line. Start engine and check for leaks. Install air cleaner. Remove plug from thermal vacuum port on throttle body.

Removal & Installation

1. Remove "FUEL PUMP" fuse from fuse block. Crank engine. Engine will start and run until fuel in lines is used. After engine stops, crank engine an additional 3 seconds to relieve remaining pressure. Turn ignition off and install fuel pump fuse.
2. Disconnect negative battery cable. Raise and support vehicle. Remove fuel tank. Turn sending unit lock ring counterclockwise. Pull lock ring away from tank. Remove fuel pump/sending unit assembly from tank. Remove pump from sending unit. To install, reverse removal procedure. Start engine and check for leaks.