Chart A-7A Fuel System Diagnosis

Ground Circuit:

Check Engine Lamp Circuit:

CIRCUIT DESCRIPTION:

When the ignition switch is turned "ON," the Electronic Control Module (ECM) and the Control Relay will turn "ON" the in-tank fuel pump under the following conditions:

1. During engine cranking.

2. Ignition "ON," engine running (ECM receiving ignition input).

3. Coolant temperature less than 1O°F, or -12°C, and ignition on for three seconds. It will remain "ON" as long as the engine is cranking or running, and the ECM is receiving an HEI distributor reference pulses. If there are no reference pulses, the ECM will shut "OFF" the fuel pump within 3 seconds after key "ON." Excess fuel is then returned to the fuel tank.

DIAGNOSTIC AIDS:

Improper fuel system pressure can result from one of the following symptoms:

1. Cranks, but won't run.
2. Cuts out, may feel like ignition problem.
3. Poor fuel economy, loss of power.
4. Hesitation.

NOTE: When engine coolant temperature is < 14°F or -10°C, 0 volts is present at terminal A3 of control relay, for 3 seconds after ignition is turned "ON" even if the engine is not cranking.