Engine Control Module - ECM

A-6 Chart:

Fuel System Flow:

Circuit Description:
When the fuel pump is running, fuel is delivered to the injector(s) and then to the regulator where the system pressure is controlled to about 62 to 90 kPa (9 to 13 psi). Excess fuel is then returned to the fuel tank. Fuel module is used on all 7.4, 5.7 over 8500 GVW.

Chart Test Description: Number(s) below refer to circled number(s) on the diagnostic chart.

1. Pressure, but less than 62 kPa (9 psi) falls into two areas:

^ Regulated pressure but less than 62 kPa (9 psi) - Amount of fuel to injector OK but pressure is too low. System will be lean running and may set DTC 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 could surge and stop when pressure is too low.

^ If pressure builds slowly or vehicle is hard starting when cold, the fuel could be draining back into fuel tank. The check valve is diagnosed in this step.

2. Restricting the outlet side of the gage allows the pump to develop its maximum pressure (dead head pressure). With battery voltage applied to the pump "test" terminal, fuel pressure should rise to 90 to 103 kPa (13 to 15 psi) as the pressure gage outlet hose is gradually pinched.

3. This test determines if the high fuel pressure is due to a restricted fuel return line or a throttle body pressure regulator problem.

Diagnostic Aids:
^ If the vehicle is equipped with a fuel module, the module must be disconnected before performing the fuel system pressure test.

^ Fuel system is under pressure. To avoid fuel spillage, refer to procedures in FUEL DELIVERY AND AIR INDUCTION/ TESTING AND INSPECTION/ PROCEDURES/ FUEL PRESSURE RELIEF Fuel Pressure Relief for testing or making repairs requiring disassembly of fuel lines or fittings.

^ On TBI engines, the fuel pressure drops to almost zero psi after pump shuts "OFF."