Part 1 of 2

Chart A-7 (1 of 2):

Wiring Diagram For Fuel Pump Relay:

Fuel System Schematic:

*** UPDATED BY TSB #91-6-14A DATE: 4/91

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 returned to the fuel tank. When the engine is stopped, the fuel pump can be energized by applying battery voltage to the fuel pump test terminal. See COMPONENT LOCATIONS for the proper location of the test terminal.


TEST DESCRIPTION: The numbers below refer to circled numbers on the diagnostic chart.

1. Use fuel system tools J29658-D Fuel Pressure Gauge or equivalent, J29658-82 O-ring Fuel Fitting Adapter or equivalent, and J29658-85 Fuel Pressure Gauge Adapter or equivalent in order to check fuel system pressure. 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 portion of the chart will verify the operation of the "wet" fuel system. If the fuel pump relay circuit is suspected of causing a extended cranking time, see CHART A-5.
3. 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:
^ Cranks, but won't run
^ Code 44 or 45
^ Cuts out
^ Poor fuel economy, loss of power.
^ Rough idle
^ Hesitation