Chart C-4A - Checking Ignition System
NOTE:
Test numbers refer to test numbers on diagnostic chart.
- Check 2 different spark plug wires to ensure an open is not present. 1A) If spark occurs with EST connector disconnected, pick-up coil output is too low for EST operation.
- A spark indicates problem is distributor cap or rotor.
- Normally there should be battery voltage at "C" and "+" terminals. Low voltage indicates an open or a high resistance circuit from the distributor to the coil or ignition switch. If voltage at "C" terminal is low, but voltage at "+" terminal is 10 volts or more, circuit from "C" terminal to ignition coil or ignition coil primary is open.
- Check for a shorted module or grounded circuit from the ignition coil to the module. The distributor module should be turned off so normal voltage (12 volts) is present. If module is turned on, the voltage should be low, but more than one volt. Failure of this test can cause ignition coil to fail due to excessive heat. With an open ignition coil primary winding, a small amount of voltage will leak through the module from the "+" terminal to tachometer terminal.
- Applying a voltage of 1.5-8 volts to module terminal "P" should turn module on, and voltage at the tach terminal should drop to 7-9 volts. This test determines if the module or coil is faulty, or if the pick-up coil is not generating the proper signal to turn module on. This test can be performed using a DC battery of 1.5-8 volts. Test light is used to allow the "P" terminal to be probed more easily. Some digital multimeters can be used to trigger the module by selecting ohms, usually the diode position. In this position the meter may have a voltage across its terminals, which can be used to trigger module.
- This should turn off the module and cause a spark. If no spark occurs, the fault is most likely in the ignition coil.