Hot Rod Forum : Hotrodders Bulletin Board - View Single Post - MSD coil testing
View Single Post
  #4 (permalink)  
Old 02-05-2006, 08:54 PM
IgnitionMan IgnitionMan is offline
Join Date: Dec 2005
Location: Yerington, Nevada
Posts: 103
Wiki Edits: 0

Thanks: 0
Thanked 0 Times in 0 Posts
Coil in cap GM HEI coils are NOTORIOUS for failing, as they are epoxy filled and do not leach heat from their cores, and run in a covered atmosphere. Their failures are usually enough to kill the HEI module if severe enough.

The failure is usually a layer short in the primary windings, and also usually causing failure of the module by resistance change and trigger side overloading, BUT, it usually isn't readable with an ohm meter.

I suggest the coil and module be removed from the distributor and taken to a parts store with the new style run testers. Most Auto-Zone's have these new type testers, and they actually rely on a running test, NOT just resistance checking.

You also need to make sure the contact points from the small black wire to the coil yoke, and the yoke to the brounding buss bar underneath it are clean and in good contact. In cap HEi coils don't use a floating ground like a regular coil does, they use a dedicated grounding of their outer yoke, and if the ground path isn't clean and tight, no spark. The ground buss bar connects the coil yoke to the module wire hold down screw in the distributor body, via the center wire in the three wire loom and connector to the cap, grounding the coil.

Best thing to do with that epoxy coil is remove it, add an MSD 8401 cap adapter, a section of coil wire, and either NAPA IC12 or MSD 8200 OIL FILLED coil instead of the epoxy filled coil, or epoxy filled "performance" coil. In short, get that coil out of the cap.

Last edited by IgnitionMan; 02-05-2006 at 09:00 PM.
Reply With Quote