Hei coil

69hurstolds

Geezer
Supporting Member
Jan 2, 2006
6,854
113
unless you're doing something weird, the original issue ACDelco coils should last for YEARS with proper maintenance during cap changeovers. If you're hooking up strange stuff to the coil and distributor like aftermarket tachs without proper filters, etc., all bets are off, but if you are simply running stock, those jokers are pretty reliable. Could they be better? Sure. So can everything. But for a mass-produced hunk of steel and tiny wires, history is all the proof you need. I have never personally been in the position of having to replace the coil in a stock HEI unit. Just make sure the red/white and red/yellow wires are correct for your application. Olds usually ran red/white, where Chebby, Caddy, and some Toros used red/yellow. Polarity is swapped.

Can't necessarily say that for the "new" ACDelco Chinesium parts are dead nuts reliable, however.
 
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airboatgreg

Comic Book Super Hero
Oct 2, 2016
2,750
113
There are several issues with having the coil located in the cap. First they run hotter under the dust cap than external coils. In order to fit in such a tight space the coils use thinner wire in the windings and thinner insulation than most external coils, weaker construction. Having the coil located in the cap also induces more interference into the pickup coil and ignition module.
Thinking back i don't remember coil failures unless there was a mitigating circumstance like an ignition problem, lack of maintenance, poor workmanship or just a cheap no name part. The location in the cap is actually pretty good when you factor the locations that some coils are placed. Still best set up ever made.
 

Clone TIE Pilot

Comic Book Super Hero
Aug 14, 2011
3,319
113
Galaxy far far away
For sure but as said, those original parts rarely failed. I sure wouldn't be in a hurry to swap to the factory small cap. I am looking at owning a 88 to 95 truck, if it develops a miss, I know what to check first. We have a lot of gravel roads, maybe the vent plugs? Those trucks always got the Blue Streak Premium cap and rotors. I just assembled a cap in coil HEI yesterday. The Accel tan cap and rotor had instructions with a picture, which mentioned the contact goes in first then the gasket. It also came with dielectric grease. I used a MSD low ohm contact and there gasket, which is black vs Accel's orange. I used the Accel Brute Thunder coil which includes a tan dust cover, so it looks stock. View attachment 196800

Thinking back i don't remember coil failures unless there was a mitigating circumstance like an ignition problem, lack of maintenance, poor workmanship or just a cheap no name part. The location in the cap is actually pretty good when you factor the locations that some coils are placed. Still best set up ever made.


In the 80's GM had a rash of coil failures in Monte Carlos. First they switched to colder spark plugs and decreased plug gaps, then the switch to external coils in 87. Putting the coil in the cap places size limits on the coil which in turns puts limitations on coil design and construction. So a quality NOS unit is already on the razor edge and it doesn't take much cost cutting to put a sub par aftermarket in cap coil over the edge. This also means there are limitations on how much improvement a aftermarket performance coil can have over stock. Again, due to the size limits, performance in cap coils have to use thinner wires in order to fit in more windings over stock. A external coil can be built with thicker wires and run cooler. The hotter a coil runs, the less current it can flow which weakens the spark..

The other big problem with coil in cap is that all the RFI and EMI the coil produces is directed into the ignition module and pickup coil. Ignition coils produce a lot of noise that interferes with the close by HEI electronics. This interference promotes false triggerings that causes misfires. Its really best to convert HEI to both remote coil and remote module to improve reliability. GM HEI was designed for low emissions, not for high performance. That is not to say coil in cap is bad, just that it has some flaws for high performance use.
 

69hurstolds

Geezer
Supporting Member
Jan 2, 2006
6,854
113
Chevy also put the starter on the wrong side of the engine where the oil filter should be, so there's that. :)
 
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69hurstolds

Geezer
Supporting Member
Jan 2, 2006
6,854
113
No chevy engine for you! :p
Too late. I got way too many of them.

Just yankin' your chain.

Just for S&G's, you could simply TRY boosting octane a bit with a good octane booster. I know you said last resort, as it should be, but right now the cause is still a mystery. Mix up 5 gallons of boosted, and once you drive until darn near empty, add the 5 gallons, see if it If the pinging stops. Then you might find you're on the right track without fiddle f*king with anything and knocking something else out of adjustment.

Without any scientific evidence, though, I believe your pinging has more to do with timing and/or fuel quality/mixture at that particular RPM. Fattening up the jets like that should have cleared any mixture problems, though. I'm going with what was mentioned earlier about pulling timing a tad at the RPM the event is happening and see if that helps. Not sure if you can do that with your electronic gizmo or not, but if you can, it's worth a try. There's a reason it's pinging, and you just have to find it, is all.
 
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Ernest

Master Mechanic
Apr 28, 2016
349
63
Texas
Too late. I got way too many of them.

Just yankin' your chain.

Just for S&G's, you could simply TRY boosting octane a bit with a good octane booster. I know you said last resort, as it should be, but right now the cause is still a mystery. Mix up 5 gallons of boosted, and once you drive until darn near empty, add the 5 gallons, see if it If the pinging stops. Then you might find you're on the right track without fiddle phuking with anything and knocking something else out of adjustment.

Without any scientific evidence, though, I believe your pinging has more to do with timing and/or fuel quality/mixture at that particular RPM. Fattening up the jets like that should have cleared any mixture problems, though. I'm going with what was mentioned earlier about pulling timing a tad at the RPM the event is happening and see if that helps. Not sure if you can do that with your electronic gizmo or not, but if you can, it's worth a try. There's a reason it's pinging, and you just have to find it, is all.
Its lQQkin that way(timing issue) with everyone else chiming in with the same suggestion about my pinging debacle. Thanks

As for the GM HEI coil in cap all in one unit, i've been very please since its inseption in '75, i started off with the mallory coil/unilite distributor combo back in the mid 90s, had to use a ballast resistor with it as well, ran great, i just didnt care for it, so out it went, sold it off, got my hands on a used GM HEI unit, rebuilt it competely and there it ran hapily in my '75 chevelle for well over a decade till i sold the car.
 

dadep76

Apprentice
Thread starter
May 11, 2021
78
8
Thanks everyone for the help. It was that the carbon spring were installed out of order. Shes back up and running great. I appreciate you guys.
 
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Clone TIE Pilot

Comic Book Super Hero
Aug 14, 2011
3,319
113
Galaxy far far away

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