DESCRIPTION & OPERATION
Throttle Body Injection (TBI) uses a low pressure electric fuel pump to supply fuel to the injectors. The fuel pump is mounted in the fuel tank, attached to sending unit. A relay controls pump operation.
When ignition switch is turned to "ON" position, the Electronic Control Module (ECM) turns on the fuel pump relay for 2 seconds. If engine is not started within this two second period, the ECM shuts off the fuel pump. As soon as the engine is cranked again, the ECM turns the relay on and runs the fuel pump.
On the 5.7L engine in the G van and all other 5.7L or 7.4L engines in vehicles over 8500 GVW, a fuel module will override the ECM and the fuel pump will run for approximately twenty seconds. The fuel module corrects a hot restart vapor lock during a high ambient condition.
As a back-up system to the fuel pump relay, the fuel pump can also be turned on by the oil pressure switch. When the engine oil pressure reaches about 4 psi (.28 kg/cm 2 ) through cranking and the fuel pump relay does not complete the circuit, the oil pressure switch will close to complete the circuit to run the fuel pump. An inoperative fuel pump relay can result in long cranking time, particularly when the engine is cold.
FUEL PUMP PRESSURE TEST
| CAUTION | Before disconnecting fuel line to connect pressure tester, fuel line pressure relief procedures must be completed. |
- Place transmission in Park (Neutral for manual transmission) and apply parking brake. Loosen fuel filler cap to relieve tank pressure.
- On 2.5L Engine, disconnect 3 terminal electrical connector at fuel tank. Start engine and let run until engine dies from lack of fuel. Crank engine for 3 seconds to relieve residual pressure. Reconnect electrical connector. On all other engines, an internal constant bleed feature automatically relieves fuel system pressure when engine is off.
- Plug thermac vacuum port on TBI (if equipped). Disconnect flexible fuel hose and install pressure gauge. Start engine and observe fuel pressure. See «FUEL PUMP PRESSURE SPECIFICATIONS»(/gmc/value-van-p3500/1985-1993/remont/testing-diagnostics/#fuel-pump-electric) . Relieve fuel pressure. Remove pressure gauge and reconnect fuel line using new "O" ring.
| Application | Psi (kg/cm 2 ) |
|---|---|
| All Models | 9-13 (.63-.91) |
FUEL PUMP PRESSURE SPECIFICATIONS
Removal & Installation
- Relieve fuel system pressure as described in «FUEL PUMP PRESSURE TEST»(/gmc/value-van-p3500/1985-1993/remont/testing-diagnostics/#fuel-pump-electric__fuel-pump-pressure-test) . Disconnect negative battery cable at battery. Raise vehicle and remove fuel tank. Remove sender unit and pump by turning cam lock counterclockwise using Tool J-36608 or J-24187.
- 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.
Note. When installing sending unit, DO NOT fold or twist strainer. This will restrict fuel flow.
SPECIFICATIONS
Note. Specifications not available. Refer to specifications within appropriate TESTING subject in this article.