Chart C-4C, Ignition System Check
NOTE:
Test numbers refer to test numbers on diagnostic chart.
- Two spark plug wires are checked to ensure open circuit does not exist in a spark plug wire. 1A) If spark exists with 4-terminal distributor disconnected, pick-up coil output is too low for Electronic Spark Timing (EST) operation.
- Spark indicates problem is distributor cap or rotor.
- Battery voltage should exist at "C" and "+" terminals. Low voltage would indicate an open circuit or a high resistance circuit from distributor to ignition coil or ignition switch. If "C" terminal voltage is low, but "+" terminal voltage was 10 volts or more, wiring circuit from terminal "C" to ignition coil or ignition coil primary circuit is open.
- This checks for a shorted distributor module or grounded circuit from ignition coil to distributor module. Distributor module should be turned off. Normal voltage should be approximately 12 volts. If distributor module is on, voltage would be low, but greater than one volt. This could cause ignition coil to fail from excessive heat. With open circuit in ignition coil primary winding, a small amount of voltage will pass through distributor module from BATT terminals to the TACH terminal.
- Applying 1.5-8 volts to terminal "P" on distributor module, should turn distributor module on and voltage on TACH terminal to decrease to approximately 7-9 volts. This determines if distributor module or ignition coil is defective or if pick-up coil is not generating proper signal to turn distributor module on. Test can be performed using a 1.5-8 volt DC battery. Test light is used to probe the "P" terminal. Some digital meters can be used to trigger distributor module by selecting ohms, usually the diode position. In this position, digital meter may have voltage across the terminals which, will trigger distributor module.
- This should turn distributor module off and cause a spark. If no spark occurs, ignition coil is probably defective, as defective distributor module would have been determined by this time.