Roadmaster V8-305 5.0L (1992)
Chart A-7 Wiring Diagram
Fuel System Schematic
CIRCUIT DESCRIPTION:
When the ignition switch is turned to the "ON" position, the ECM will activate the in-tank fuel pump. The fuel pump will operate as long as the engine is
cranking or running, and the ECM receives an ignition reference pulse. If no ignition reference exist, the ECM will no longer supply the fuel pump relay
a voltage signal after 2 seconds once the ignition is "ON." The fuel pump will supply fuel to the TBI unit where the pressure is controlled from 9 to 13
psi (62 to 90 kPa) by the pressure regulator. Excess fuel is then returned to the fuel tank. When the engine is stopped, the pump can be energized by
applying battery voltage to the fuel pump test terminal. See LOCATIONS/COMPONENTS/UNDERHOOD BLOCK DIAGRAMS for the proper
location of the test terminal.
TEST DESCRIPTION: The numbers below refer to circled numbers on the diagnostic chart.
1.
Fuel pressure should be noted while the fuel pump is running. Fuel pressure will drop immediately after the fuel pump stops running due to a
controlled bleed in the fuel system.
2.
This check will verify the operation of the fuel pump check valve. A leaking check valve will cause fuel in the pressure line to drain back into the
tank, which will result in extended cranking times. The amount of pressure is not important as long as some pressure is maintained.
DIAGNOSTIC AIDS:
Improper fuel system pressure may result in one of the following symptoms:
^
Extended cranking time before the engine starts.
^
Rough idle.
^
Low idle speeds.
^
Cranks, but won't run
