Chart C-4A Ignition System Check

Fig. 011 - Chart C-4A Ignition System Check (Integral Ignition Coil):

Procedure
1. Checks for proper output from the ignition system. The ST-125 requires a minimum of 25,000 volts to fire. This check can be used in case of an ignition miss because the system may provide enough voltage to run the engine but not enough to fire a spark plug under heavy load.

Note: If the engine will start with the connector disconnected, it indicates the problem is related to the EST circuit. The problem would usually be a grounded EST line or no ground to the ECM.

2. Normal reading during cranking is about 9-10 volts.
3. Checks for a shorted module or grounded circuit from the ignition coil to the module. The distributor module should be turned off so normal voltage should be about 12 volts. If the module is turned "ON," the voltage would be low but above 1 volt. This could cause the ignition coil to fail from excessive heat. With an open ignition coil primary winding, a small amount of voltage will leak through the module from the "Bat." to the tach terminal.
4. Checks the voltage output with the pick-up coil triggering the module. A spark says the ignition system has enough output, but intermittent no-starts or poor performance can result if the polarity of the ignition coil and pick-up coil is not correct.
The color of the pick-up coil connector has to be yellow if one of the ignition coil leads is yellow. If the ignition coil has a white lead, any pick-up coil connector color except yellow is OK.
5. Checks for an open module or circuit to it. 12 volts applied to the module "P" terminal should turn the module "ON" and the voltage should drop to about 7-9 volts.
6. This should turn off the module and cause a spark. If no spark occurs, the fault is most likely in the ignition coil because most module problems would have been found before this point in the procedure. A module tester could determine which is at fault.