Fuel System Diagnosis

CHART 1 OF 1





DIAGNOSTIC CHART





WIRING DIAGRAM

INSPECTION PROCEDURE

Circuit Description:
When the ignition switch is turned "ON", the Engine Control Module (ECM) will turn "ON" the in-tank fuel pump. It will remain "ON" as long as the engine is cranking or running, and the ECM is receiving ignition reference pulses.
If there are no reference pulses, the ECM will shut "OFF" the fuel pump within 2 seconds after key "ON".
The pump will deliver fuel to the Throttle Body Fuel Injection unit, where the system pressure is controlled to 62 to 90 kPa (9 to 13 psi). Excess fuel is then returned to the fuel tank.
The fuel pump test terminal is located in the left side of the engine compartment. When the engine is stopped, the pump can be turned "ON" by applying battery voltage to the test terminal.

Test Description:
Number(s) below refers to circled number(s) on the diagnostic chart.
1. Fuel pressure should be noted while fuel pump is running. Fuel pressure will drop immediately after fuel pump stops running due to a controlled bleed in the fuel system.

Diagnostic Aids:
Improper fuel system pressure can result in one of the following symptoms:
- Cranks, but will not run.
- Diagnostic Trouble Code (DTC) 44.
- DTC 45.
- Cuts out, may feel like ignition problem.
- Poor fuel economy, loss of power.
- Hesitation.

CHART 2 OF 2





DIAGNOSTIC CHART





WIRING DIAGRAM

INSPECTION PROCEDURE

Test Description:
Number(s) below refer to circled number(s) on the diagnostic chart.
1. Fuel pressure less than 62kPa (9 psi) falls into two areas:
- Regulated pressure less than 62 kPa (9 psi). Amount of fuel to injectors OK but pressure is too low. System will be lean and may set Diagnostic Trouble Code 44. Also, hard starting cold and poor overall performance.
- Restricted flow causing pressure drop. Normally, a vehicle with a fuel pressure of less than 62 kPa (9 psi) at idle will not be drivable. However, if the pressure drop occurs only while driving, the engine will normally surge then stop as pressure begins to drop rapidly.
2. Restricting the fuel return line allows the fuel pump to develop its maximum pressure (dead head pressure). When battery voltage is applied to the pump test terminal, pressure should be from 90 to 124kPa (13 to 18 psi).
3. This test determines if the high fuel pressure is due to a restricted fuel return line or a throttle body pressure regulator problem.