Diagnostic Aids

Major difference between Computer Controlled Dwell (CCD) and non-CCD systems is CCD system does not receive a start signal from ignition switch at ICM (terminal No. 4) during engine cranking. CCD systems send an additional coil negative (-)/tach circuit signal to PCM from ignition module (terminal No. 4) labeled Filtered Tach Output (FTO). Following information should be noted during testing:

• All voltage readings given in test procedures are based on values obtained using a standard DVOM such as Rotunda (007-00001) or Fluke (20 or 70 Series). DO NOT use RMS type meter.
• When instructed to inspect a wiring harness, perform both a visual inspection and a continuity test.
• When making voltage checks, ground connections should be made at negative battery terminal or cast iron surface of engine.
• When making measurements on a wiring harness or connector, perform a wiggle test while measuring.
• When making voltage checks, ground readings are defined as a value of less than 1.0 volt. Battery voltage is defined as a value of 10-14 volts.
• Test procedures are intended to identify faulty components or wiring while fault is present. If complaint is an intermittent condition, refer to appropriate H - EEC-IV TESTS W/O CODES article in the ENGINE PERFORMANCE Section.