A-7 ~ Fuel System Diagnosis

Chart A-7 Wiring Diagram:

Chart A-7 - Fuel System Diagnosis (1 Of 2):

Chart A-7 - Fuel System Diagnosis (2 Of 2):

CIRCUIT DESCRIPTION:
When the ignition switch is turned "ON," the Electronic 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 TBI 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 below refers to circled number 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 won't run
- Code 44
- Code 45
- Cuts out, may feellike ignition problem
- Poor fuel economy, loss of power
- Hesitation
TEST DESCRIPTION: Numbers below refer to circled numbers on the diagnostic chart.
1. Pressure less than 62 kPa (9 psi) falls into two areas:
- Regulated pressure under 62 kPa (9 psi). Amount of fuel to injectors OK but, pressure is too low. System will be lean and may set 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 driveable. 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 development its maximum pressure (dead head pressure). When battery voltage is applied to the fuel pump test terminal, pressure should from 90 to 124 kPa (13-18 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. Apply battery voltage to the fuel pump "test" connector only long enough to get an accurate fuel pressure reading.