Table A-7B Fuel System Diagnosis (Fuel Pressure Check)

Table A-7B Fuel System Diagnosis (Fuel Pressure Check) (1 Of 2):

Table A-7B Fuel System Diagnosis (Fuel Pressure Check) (2 Of 2):

Fuel System:

CIRCUIT DESCRIPTION

When the ignition switch is turned to the "ON" position, the Engine Control Module (ECM) will energize the fuel pump relay for 3 seconds, allowing for fuel pump operation. If the engine is being cranked, or is running, the fuel pump will continue to operate, as long as the ECM is receiving ignition reference pulses. If the ignition reference pulses are not detected, the fuel pump will stop after 3 seconds.


The fuel pump will deliver fuel through the fuel filter and fuel rail to the fuel injectors and fuel pressure regulator, where the system pressure is controlled at 250-300 kPa (36-43 psi) with the ignition switch in the "ON" position and 210-260 kPa (30-37 psi) with the engine idling at normal operating temperatures. Excess fuel is then returned to the fuel tank.


DIAGNOSTIC AIDS

Improper fuel system pressure can result in one of the following conditions:

- Cranks, but will not run.

- Cuts out, may feel like an ignition malfunction.

- Poor fuel economy, loss of power.

- Hard starts.

One minute after the fuel pump stops, fuel pressure should hold at approximately 180 kPa (25 psi).

If fuel pressure is normal and symptoms still exist, Refer to Symptoms. Testing and Inspection

TEST DESCRIPTION

Number(s) below refer to the step number(s) on the Diagnostic Table.


1. The Engine OBD System Check prompts the technician to complete some basic checks and store the freeze frame data on the scan tool if applicable. This creates an electronic copy of the data taken when the fault occurred. The information is then stored in the scan tool for later reference.

2. Checks to see if fuel system pressure is within specifications with the ignition "ON," and the fuel pump running.

3. Checks the fuel pressure after the fuel pump stops. Approximately one minute after the fuel pump stops fuel pressure should stay steady at 180 kPa (25 psi).