HEI Coil Check
 

How do you check to see if your coil is going bad?, been running my street car at the Drags on test and tune night. been running fine except a lean stumble out of the hole, a re-jetting fixed that, but it started to "miss out" in high gear seemed to get worse every run. the coil is 17 years old (Accell HEI Super Coil) everything else in Dist is newer, was rebuilt by Suntuned a few years back, so i thought that would be the first thing to check. car sets alot, doesn't get driven very often, fuel system is new from this spring, #8 line, Holley Red pump, fuel cell, etc, cars best run to date 12.93 at 103mph, mild 406, Th 350, 3.90 gears.

You can check the resistance of the windings, but you usually can't see high-voltage shorts to the coil frame. I think the only really accurate test is a substitute coil.

Make sure the coil ground strap is installed in the cap. A missing one causes premature coil failure.

See if you can put the engine under load in a dark garage and use a spray bottle of water and spray the coil and the wires and look for arcing. Maybe there is some carbon tracking going on. :)

found the problem, it was the pickup coil, checked it with the vac advance unplugged, replaced it and it runs fine now!