Chart A-7A Fuel System Diagnosis

Fig. 022 - Chart A-7A Fuel System Diagnosis.:

CHART A-7A

FUEL SYSTEM DIAGNOSIS

2.8L "X" SERIES
FUEL INJECTION (PORT)

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 HEI distributor reference pulses.
If there are no reference pulses, the ECM will shut "OFF" the fuel pump within 2 seconds after key "ON" or engine stopped.
The pump will deliver fuel to the fuel rail and injectors, then to the pressure regulator, where the system pressure is controlled to about 234 to 317 kPa (34 to 46 psi). Excess fuel is then returned to the fuel tank.

Chart A-7A Fuel System Diagnosis:

1. Use a pressure gage. Wrap a shop towel around the fuel pressure tap to absorb any small amount of fuel leakage that may occur when installing the gage.

Ignition "ON" pump pressure should be 280-325 kPa (40.5-47 psi). This pressure is controlled by spring pressure within the regulator assembly.

2. When the engine is idling, the manifold pressure is low (high vacuum) and is applied to the fuel regulator diaphragm. This will offset the spring and result in a lower fuel pressure. This idle pressure will vary somewhat depending on barometric pressure, however, the pressure idling was less indicating pressure regulator control.
3. Pressure that continues to fall is caused by one of the following:
a. In-tank fuel pump check valve not holding.
b. Pump coupling hose leaking.
c. Fuel pressure regulator valve leaking.
d. Injector sticking open.
4. An injector sticking open can best be determined by checking for a fouled or saturated spark plug(s). If a leaking injector can not be determined by a fouled or saturated spark plug the following procedure should be used.
a. Remove Plenum, cold start valve and remove fuel rail bolts. Leave fuel lines connected.
b. Reconnect cold start valve.
c. Connect a hose to valve nozzle and insert into a gasoline container .
d. Lift fuel rail out just enough to leave injector nozzles in the ports.
CAUTION: BE SURE INJECTOR(S) ARE NOT ALLOWED TO SPRAY ON ENGINE AND THAT INJECTOR RETAINING CLIPS ARE INTACT. THIS SHOULD BE CAREFULLY FOLLOWED TO PREVENT FUEL SPRAY ON ENGINE WHICH WOULD CAUSE A FIRE HAZARD.
e. Pressurize the fuel system.
if. Lift each side of rail up and observe for injector(s) leaking.

Fig. 022 - Chart A-7A Fuel System Diagnosis.:

Chart A-7B Fuel System Diagnosis:

CHART A-7B

FUEL SYSTEM DIAGNOSIS

2.8L "X" SERIES, "A" SERIES
FUEL INJECTION (PORT)

1. Pressure but less than 280 kPa (40.5 psi) falls into two areas:
a. Regulated pressure but less than 280 kPa (40.5 psi) Amount of fuel to injectors OK but pressure is too low. System will be lean running and may set Code 44. Also, hard starting cold and overall poor performance.
b. Restricted flow causing pressure drop - Normally, a vehicle with a fuel pressure of less than 165 kPa (24 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 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 above 414 kPa.(60 psi)
3. This test determines if the high fuel pressure is due to a restricted fuel return line or a pressure regulator problem.