Chart A-5 Fuel System Electrical Test

Chart A-5, Fuel Supply System Electrical Test:

Fuel Pump/Relay Circuit Diagram:

CIRCUIT DESCRIPTION:

When the ignition switch is turned "ON", the PCM will energize the fuel pump relay which turns "ON" the in-tank fuel pump. It will remain "ON" as long as the engine is cranking or running, and the PCM is receiving distributor reference pulses. If there are no reference pulses, the PCM will de-energize the fuel pump relay which will shut "OFF" the fuel pump within 2 seconds after ignition key is turned "ON" or the engine stops.

The fuel pump will deliver fuel to the fuel rail and injectors, then to the pressure regulator where the system pressure is controlled. Excess fuel pressure is bypassed back to the fuel tank. When the engine is stopped, the pump can be turned "ON" by applying battery voltage to the test terminal located in the engine compartment using a fused jumper harness.

Improper fuel system pressure may contribute to one or all of the following symptoms:

^ Cranks but won't run
^ Code 44 or 45
^ Cuts out, may feel like ignition problem
^ Hesitation, loss of power or poor fuel economy


TEST DESCRIPTION
Numbers below refer to circled numbers on the diagnostic chart.
1. Check for the fuel pump relays power CKT 839 and ground CKT 450.

2. Checks that PCM is supplying voltage to fuel pump relay. The PCM should energize the fuel pump relay and turn the fuel pump "ON" during engine cranking, or for about 2 seconds when the ignition switch is turned "ON". Once the engine starts, a switch in the engine oil pressure sensor provides power to the fuel pump. If the ignition reference pulse to the PCM is lost while the engine is running, the fuel pump relay will remain energized as long as there is sufficient engine oil pressure to "close" the fuel pump switch in the oil pressure sensor.

3. This checks for an open in CKT 465.