Computers and Control Systems: Testing and Inspection

Fig. 45 Detonation control unit test:

1. Run engine at idle until normal operating temperature is reached.
2. Disconnect detonation sensor electrical connector with engine idling.
3. Slowly increase engine speed and check ignition timing with a suitable timing light.
4. If timing retards 10° when engine speed increases more than 2000 RPM, replace detonation sensor.
5. If timing does not retard, measure voltage between detonation control unit terminal No. 4, Fig. 45, and ground with engine running above 2000 RPM. If voltage measures .4-.7 volts, proceed to step 6. If voltage does not measure .4-.7 volts, check distributor and wiring harness and repair as necessary.
6. Measure voltage between detonation control unit terminal No. 3 and ground with engine running above 2000 RPM. If voltage does not measure 3.7-3.8 volts, replace detonation control unit.