Chart A-4A Fuel System Diagnosis (Circuit Test)

Diagnostic Chart.:

Fuel System Wiring Schematic:

DESCRIPTION:

This procedure tests for fuel supply system problems that can cause incorrect fuel pressure or incorrect fuel pump operation.

NOTES ON FAULT TREE:

1. Fuel pressure above 50 psi is caused either by a malfunction of the pressure regulator or by a restriction in the fuel return line. It should be noted that secondary conditions of spark plug fouling, codes E043 and E045, or oxygen sensor contamination resulting in codes E013, E017, E043, and E045 may result from the too rich fuel flow. To isolate the cause of the high fuel pressure, disconnect the return line at the fuel rail and connect a suitable fitting to the fuel rail which will accept a length of flexible rubber fuel hose. Insert the other end of the hose into a suitable fuel container and observe the fuel pressure as the ignition switch is turned on., If the fuel pressure remains above 50 psi, replace the fuel pressure regulator--it is unable to control pressure properly. If the fuel pressure drops below 50 psi, with the fuel return line bypassed, then the fuel return line is restricted. A restricted fuel return line can be diagnosed by visually inspecting the line for kinks, damage, etc. A kink in the Teflon fuel line (braided stainless steel clad) may not be visually obvious.

2. If the fuel pump relay or PCM were the cause of a low fuel pressure, there would be a PCM code E20 set. This step is to check for voltage supply to the fuel tank five-way connector.

3. If the voltage signal to the fuel tank connector is OK, then an open may exist between the five-way fuel tank connector and the fuel pump. If fuel pump runs with an alternative power source connected, the fuel tank unit is OK; check fuel pressure regulator for cause of low pressure.

4. Checking for fuel supply system (tank, filter, pump, sender, supply line) able to deliver at least 40 psi pressure or for fuel pressure regulator fault.