HEI module dwell time.

MikeB said:

I've heard a lot about module failures over the years and guys carrying spares. But I've installed several HEIs in 50s-70s project vehicles starting in mid-1990s, and none of those ever had a module, pickup, or coil failure. Some had stock internals, others were upgraded to MSD module, coil, rotor, and cap back when those kits were made in the USA and reasonably priced. Also put a Proform HEI in my 82 C10 in 2015.

I also had stock GM HEIs in four 74-81 Chevy and Buick daily drivers that I can think of. None of them ever failed. However, your comments and others make me want to carry a spare module. Just need to find one that isn't Chinese junk. What do you all recommend?

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MikeB said:

I've heard a lot about module failures over the years and guys carrying spares. But I've installed several HEIs in 50s-70s project vehicles starting in mid-1990s, and none of those ever had a module, pickup, or coil failure. Some had stock internals, others were upgraded to MSD module, coil, rotor, and cap back when those kits were made in the USA and reasonably priced. Also put a Proform HEI in my 82 C10 in 2015.

I also had stock GM HEIs in four 74-81 Chevy and Buick daily drivers that I can think of. None of them ever failed. However, your comments and others make me want to carry a spare module. Just need to find one that isn't Chinese junk. What do you all recommend?

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Matt69olds said:

When HEI first came out, the modules did have some reliability issues. It didn’t take long for Delco to figure it out and solve the issue. Unfortunately, the bad reputation still lingers.

Even counting the time working in a dealership service department , I bet I have only replaced a dozen ignition modules over the years. I have never personally had one fail in one of my vehicles, however I did have a friend who’s car would die after it got hot.

If someone is having repeated module failure, either they are using junk parts, or the aren’t using the correct THERMAL heat transfer paste. Don’t use dielectric grease!!

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bucket said:

What is a common place that heat paste can be bought?

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bucket said:

I've had a couple coils fail and at least one pickup coil, but can't remember any modules (of the large cap variety) failing on my own vehicles. I remember several customer vehicles with a failed module though. I read on here a while back that the Napa Echlin TP-55 (going off memory here) was a good one to buy, so that's what I have as spares.




I know we've had the discussion about the paste a few times in the past. I've never had issues with using dielectric grease. However, this last time I was putting a distributor together I decided I'd use the paste... I couldn't find any. Napa was able to dig up a part number for the stuff, but it showed it was unavailable. I wound up at O'Reilly and they didn't have any either, but the guy behind the counter went picking through ignition module boxes until he found one with the heat paste packet in it. He simply gave it to me, lol.

What is a common place that heat paste can be bought?

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JD Miller said:

Really? What years models are they talking about. My 81 k20 plug gap is specs is .035 .
That article is pretty vague

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Rebuildman said:

If you are not using a GM module in your HEI distributor then there is a good possibility your dwell time is not correct thru the entire RPM range, which also affects timing. I also use TPI on some engines which uses a small cap HEI, it has no advance built into the distributor it is all controlled by the computer. In this case there is a setting in the chips program that can compensate for the different dwell characteristics of different GM modules that can be installed, its called "Latency compensation". for each different p/n, all GM modules have this offset. Any off-brand module has no information on what to set the "Latency" to, so the dwell/timing advance is corrected. Lots of testing has been done to prove how the dwell/timing advance is affected by just swapping modules without changing the latency.
Use original GM pickup/modules that are for your engine. If you can find one.

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75gmck25 said:

IIRC, .060 plug gap was an early spec for HEI, maybe when they were trying to improve the burn for emissions. Later on they found it put too much stress on the ignition to consistently fire across the wide gap, and revised the specs. I think the revised GM spec was .045, but I’m not positive. Some new plugs come gapped as small as .035.

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AuroraGirl said:

The .060 is more to do with later HEI, however, I believe oldsmobile/pontiac did some couple years with .060, but it toasted components?
I could be remembering wrong but I think i read a long time ago something about that... lol.

But .060 would be, in my opinion, a lot for a stock HEI on a 1983 to use

But a different design plug, no ribs, di-electric screws on the rotor.... it would be easier than what you currently have.

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AuroraGirl said:

Even Gen III LS engines with 8 coils had a TSB to drop the plug gap to reduce chugging and hesitation and driveability issues in the early 2000s , i think .45 was the one they used. But the normal expected gap they run is .060
The 3800 engines have been running .060 since about 1993-4 , wasted spark system on those but high quality set of 3 coils

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Camar068 said:

seeing 0.040-0.044 range on RA for 2006 LS, with a note of OE 0.040

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Matt69olds said:

Oldsmobile use to specify .080 plug gap, and then later revised it. If I remember correctly, the issue was low speed misfired and ignition component wear.

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