AMC Ignition System Electronic Spark Retard Test

1. With engine at operating temperature, disconnect vacuum switch electrical connector. The vacuum switch electrical connector is located on the wheel housing.
2. Disconnect and plug distributor vacuum advance hose.
3. Disconnect electrical connector from knock sensor and ground to engine block using a jumper wire.
4. Increase engine speed to 1600 RPM and check and adjust ignition timing as necessary.
5. Allow engine to return to idle speed, then reconnect vacuum switch electrical connector.
6. While observing timing marks, advance engine speed to 1600 RPM. Timing should advance 6° over the degree noted in step 4.
a. If timing does not advance, check for defective vacuum switch or wiring from switch to Microprocessor Computer Unit (MCU). If switch and wiring are satisfactory, replace MCU and repeat test.
b. If timing did increase, proceed to step 7.
7. Allow engine to return to idle and connect electrical connector to knock sensor. Increase engine speed to 1600 RPM, while noting timing marks, knock on intake manifold in area of knock sensor. Ignition timing should retard.
a. If ignition timing did retard, system is satisfactory. allow engine to return to idle and reconnect distributor vacuum advance hose.
b. If ignition timing did not retard, check continuity of wiring between knock sensor and MCU J2 electrical connector terminal 16 on 1983 models. On 1984-87 models check continuity between knock sensor and MCU J2 electrical connector terminal 51. If wiring is faulty, repair or replace as necessary. If wiring is satisfactory, replace knock sensor and retest.