Chart A7 (1 Of 2) - Fuel System Diagnosis (2.8L)

With the ignition on, the 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 the ignition is turned off or engine is stopped. The fuel pump will deliver fuel to the fuel rail and injectors, then to the pressure regulator, where the system pressure is controlled between 34-46 psi (2.3-3.0 kg/cm² ). Excess fuel is then returned to the fuel tank.

1. Use Pressure Gauge (J 34730 1). Wrap a shop towel around the fuel pressure tap to absorb any small amount of fuel leakage that may occur when installing the gauge. With the ignition on fuel pressure should about 40-47 psi (2.8-3.2 kg/cm² ). 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 a defective pressure regulator control.
3. Pressure that continues to fall is caused by one of the following conditions:
   • In-tank fuel pump check valve not holding.
   • Pump coupling hose or pulsator leaking.
   • Fuel pressure regulator valve leaking.
   • Injector sticking open.
4. Check for an injector sticking open by checking for a fouled or saturated spark plug. If a leaking injector can not be determined by a fouled or saturated spark plug the following procedure should be used
   • Remove plenum, cold start valve and fuel rail bolts.
   • Reconnect cold start valve.
   • Connect a hose to valve nozzle and insert into a gasoline container.
   • Lift fuel rail out just enough to leave injector nozzles in the ports.
   • Pressurize fuel system.
   • Lift each side of rail up and check for injector leaking.
5. See appropriate TROUBLESHOOTING procedures in the CEC TESTS W/O CODES article in this section.