Chart A-5, Fuel System Electrical Test
When ignition is turned on, ECM will energize fuel pump relay, which completes circuit to in-tank fuel pump. It will remain on as long as engine is cranking or running, and ECM is receiving C(3)I reference pulses. If there are no reference pulses, ECM will de-energize fuel pump relay within 2 seconds after key is turned on and engine is not running.
The fuel pump will deliver fuel to fuel rail and injectors, then to pressure regulator, where system pressure is controlled. Excess fuel pressure is by-passed back to fuel tank. When engine is shut off, fuel pump can be turned on by applying battery voltage to test terminal located in engine compartment. Improper fuel system pressure may contribute to one or all of the following symptoms:
- Cranks but won't run.
- Code EO44 or EO45.
- Cuts out, may feel like ignition problem.
- Hesitation, loss of power or poor fuel economy.
- If fuse is blown, a short to ground in circuits No. 120 and 639, or fuel pump itself is cause of problem.
- Determines if fuel pump circuit is being controlled by ECM. The ECM should energize fuel pump relay. When engine is not cranking or running with key on, ECM should de-energize relay within 2 seconds after ignition is turned on.
- This test activates fuel pump if circuit No. 120 wiring is okay. If pump runs, problem is basic fuel delivery.
- This test will determine if a short to ground in circuit No. 120 caused fuse to blow. To prevent an incorrect diagnosis, ensure fuel pump is disconnected before test.
- Checks for short to ground in fuel pump relay harness circuit No. 639.
- Checks for open in fuel pump relay ground, circuit No. 450.
- Determines if ECM is in control of fuel pump relay through circuit No. 465 (terminal "A").
- The fuel pump control circuit includes an engine oil pressure switch with a separate set of normally open contacts. The switch closes at about 4 psi of oil pressure and provides a second battery voltage feed path to fuel pump. If relay fails, fuel pump will operate using battery voltage supplied by closed oil pressure switch.
This step checks oil pressure switch, ensuring that it provides battery voltage to fuel pump should pump relay fail. A failed fuel pump relay will result in extended engine crank time, because of time required to build sufficient oil pressure to close oil pressure switch, and activate fuel pump. There may be circumstances when relay has failed, but engine will not crank fast enough to build sufficient oil pressure to close switch. This, or a faulty oil pressure switch, can result in an "Engine Cranks But Won't Run" condition.