When your classic car loses its spark it’s not too hard to find it again. The GM HEI is a pretty simple ignition to troubleshoot and sometimes the problem isn’t even at the distributor. I’m going to take you through the entire process of how to troubleshoot your ignition issue so that you can get back on the road and enjoy your classic!
Here’s a link to the electrical diagnostic checklist: snowfamilyracing.com/electrical-checklist-sign-up/
The entire process starts at the battery. We need to know what the current voltage is because without proper voltage, everything else isn’t going to work right. From the battery, the battery cables and connections both power and ground need to be sound and not dirty. GM likes to have their main power wire take off from the starter, and that nut can work loose over time and cause problems.
After that, checking the fuse and power into the fuse is the next stop on this journey. The GM tilt column can have a problem if it’s working loose at the tilt mechanism. The issues is that the rods that actuate the ignition switch and neutral safety switch can actually push the switch out of position and put power where it doesn’t belong. Tightening the 4 bolts that hold the tilt knuckle in place is the only solution for that issue.
Back to wiring, ensuring that the switch is in good working order is important because that switch sends power out to the distributor. We want to make sure that the distributor is seeing the same voltage as the battery, otherwise there’s a connection issue somewhere in line that needs to be found.
After verifying power to the distributor, check the coil to ensure that the resistance across the primary and secondary wiring is within spec. After that there’s only 2 components left. The module, which is the likely culprit, and the magnetic pick up. The magnetic pick up hardly ever fails, though it can happen and is usually verified with a lab scope.
If you’ve made it this far, you’ve likely found the source of a lost spark, that is of course if the plug wires are in decent shape. That is a pretty obvious problem that is easily corrected. With that fixed you can get back to enjoying your classic!
Other Tools used in this video:
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