Ignition Timing Control System

WITH ENGINE COLD

NOTE: Engine coolant temperature should be below 140 deg. F and intake air temperature should be below intake air temperature switch set temperature. Switch should have continuity.

1. Disconnect vacuum hose No. 8 from vacuum advance diaphragm B on distributor, then connect suitable vacuum gauge to hose.
2. Start engine and allow to idle. If vacuum is present, test system with engine hot. If vacuum is not present, check for voltage at vacuum control solenoid valve blue/black wire connector in emission box.
3. If voltage is present, replace vacuum control solenoid valve and repeat test. If voltage is not present, refer to "Troubleshooting, 1984-86 Prelude."

WITH ENGINE HOT

1. Disconnect vacuum hose No. 8 from vacuum advance diaphragm B on distributor, then connect suitable vacuum gauge to hose.
2. Start engine and allow to reach normal operating temperature. At idle, vacuum should not be present.
3. If vacuum is not present, proceed to step 5. If vacuum is present, check for voltage at vacuum control solenoid valve blue/black wire connector in emission control box.
4. If voltage is present, refer to "Troubleshooting, 1984 Prelude." If voltage is not present, replace vacuum control solenoid valve and repeat test.
5. Attach hand vacuum pump to vacuum advance diaphragms A and B using a suitable T-fitting.
6. Plug ends of advance hoses, then pinch off hose to diaphragm B.
7. Start engine, apply 16 inches Hg vacuum and record timing. Timing should advance and remain steady.
8. If timing advances, proceed to step 9. If timing will not stay advanced, replace advance diaphragm and repeat test. If timing does not advance, stop engine and remove distributor cap. Inspect breaker plate for free movement. If no binding is evident, replace advance diaphragm and repeat test.
9. Release pinched hose and apply 16 inches Hg. vacuum. Timing should advance more than recorded in step 7 and remain steady.
10. If timing advances more than previous test, system is satisfactory. If timing does not advance more than recorded in step 7, replace advance diaphragm and repeat test.


TROUBLESHOOTING 1984 PRELUDE

1. Inspect thermosensor, replace as required.
2. Check intake air temperature sensor for continuity. Continuity should be present if air temperature is below 40 deg. F. Continuity should not be present if air temperature is above 73 deg. F. If continuity is not as specified, replace sensor.
3. Check voltage at black/yellow wire of control unit connector with ignition switch in the On position. If voltage is not present, check wiring.
4. Check for continuity between black/brown wire of control unit and ground. Continuity should be present.
5. On models equipped with automatic transaxle, check for voltage at blue wire of control unit connector with ignition switch in On position. If voltage is not present, check blue wire between ignition coil and control unit.
6. Inspect speed sensor and vacuum switch C, replace as required.