Cold Advance System Diagnosis

Cold Advance Chart ECM/PCM:

Cold Advance Circuit PCM/ECM:

CIRCUIT DESCRIPTION
With the key "ON," and coolant temperature below 80°F, the ECM/PCM grounds CKT 421 to the cold advance relay. Grounding CKT 421 turns "ON" the relay, to supply 12 volts to the cold advance solenoid, in the injection pump, and the glow plug controller The cold advance solenoid is now energized, which causes the injection timing to be advanced approximately 5°.

TEST DESCRIPTION
Number(s) below refer to circled number(s) on the diagnostic chart.

1. This step will determine if the problem is electrical or a malfunction inside the injection pump.

2. This step will determine if the ECM/PCM is able to turn "ON" the cold advance relay.

3. This step will determine if all factors are available for the cold advance relay to operate.


DIAGNOSTIC AIDS
- If there is no electrical problem found, check the operation of the cold advance solenoid in the injection pump.

- Before replacing ECM/PCM, use an ohmmeter and check the resistance of each ECM/PCM controlled relay and solenoid coil. Refer to Diagrams/Electrical for coil terminal I.D. of solenoid(s) and relay(s) to be checked. Replace any solenoid where resistance measures less than 20 ohms.