Fuel Pump: Description and Operation

Fuel Supply System:

DESCRIPTION
The fuel pump is a turbine type, low pressure electric pump, mounted in the fuel tank. Fuel is pumped at a positive pressure (above 62 kPa or 9 psi) from the fuel pump through the in-line filter to the pressure regulator in the TBI unit. Excess fuel is returned to the fuel tank through the fuel return line.

The fuel pump is attached to the fuel gage sender assembly. A fuel strainer is attached to the fuel pump inlet line and prevents dirt particles from entering the fuel line and tends to separate water from the fuel.

Vapor lock problems are reduced when using an electric pump because the fuel is pushed from the tank under pressure rather than being pulled under vacuum, a condition that produces vapor.

OPERATION
When the key is first turned "ON" without the engine running, the control module turns a fuel pump relay "ON" for two seconds. This builds up the fuel pressure quickly. If the engine is not started within two seconds, the control module shuts the fuel pump "OFF" and waits for ignition reference pulses. As soon as the engine is cranked, the control module turns the relay "ON" and runs the fuel pump.

When the engine is cranking or operating, the control module receives distributor ignition reference pulses which also energize the injectors.

As a backup system to the fuel pump relay, the fuel pump is also turned "ON" by an oil pressure switch. When the engine oil pressure reaches about 28 kPa (4 psi), through cranking the oil pressure switch will close to complete the circuit to the fuel pump.

An inoperative fuel pump relay can result in long cranking times, particularly if the engine is cold. The oil pressure switch will turn "ON" the fuel pump as soon as oil pressure reaches about 28 kPa (4 psi).

In order to properly control the fuel supply, the fuel pump is operated by the control module through the fuel pump relay and oil pressure switch refer to CHART A-5. Under Computers and Control Systems/System Diagnosis/Procedures/Diagnostic Charts. Testing and Inspection

COMPONENTS
The fuel supply system consists of the following components:

- Fuel pump.
- Fuel tank.
- Accelerator control components.
- Fuel lines.
- Fuel filter.