Which Ignition Control Module do I need....ACDelco D1943A or D1984A ?

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I am trying to find out which ACDelco ICM is correct for my truck.....D1943A or D1984A. The info on Rockauto shows the D1943A is for "W/O HEI". I guess then D1984A means for HEI distributor. I also went to ACDelco's web site and entered my VIN, and it lists both ICMs for my truck, again with the "W/O HEI" notation for the D1943A.

My VIN is 2GCEC19K0R1134189. The VIN decoder shows I have K code engine L05.

My distributor has the coil mounted separately in front of it. The electrodes on top of the distributor cap are "male". I have looked all over the web and it seems people use both ICMs. Also, apparently there are several variations out there of HEI distributors, with the coil built into the distributor cap or mounted separately in front of it.

A few years ago, while driving down the freeway, my truck just quit. Crank, no start. Had it towed home and started checking and reading. I ended up ordering a D1943A module put it in and the truck stated and has run fine ever since. But now that I have found out about the D1984A, I'm wondering if I have the wrong ICM in it, and it's running ok inspite of it?

Can anyone tell me for sure which ICM I should have in my distributor? How can I tell if mine is non-HEI or HEI for sure? I have done a VIN decoder sheet and it does not say anything other than it is a K code engine, L05.

 

[PlayingWithTBI]

FWIU the D1943A is also for the 4&6 cyl engines, aside from HEI or not, where the D1984A is for an 8 cyl engine. The 87-95 TBI distributor is a "small cap HEI".

 

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[Rain]

This is the distributor cap (ACDelco D303A) that has been on the truck since I bought it in 2015. Is it a "small cap HEI"? It gets very confusing. No less than ACDelco themselves show both ICMs for my 1994. It seems more people run the D1943A than the 1984. If I can, I am trying to narrow it down to which one is "supposed" to be right for my truck. The ACDelco web site shows this number as the only right dist. for my truck: 19179575

 

[PlayingWithTBI]

YeP, that's a small cap HEI where the ICM sits under that opening.

 

[Rain]

I think I have gotten to the bottom of it......I called ACDelco (800-223-3526), and with my VIN, he said the D1943A is the correct ICM. He said that was the only ICM listed for my truck, and he didn't show the D1984A as appropriate, even though his web site for consumers that I used does also show the D1984A, and Rockauto also shows them both. I pressed him why when I enter my VIN on their site, it comes back with both ICMs. He just said that internally, they have other resources available that is for their employees, etc. He said with my VIN, he can see exactly how they originally built it with what parts.

So I also asked him to look up the D1984A and see if it showed any other relevant info. He did, and he said that ICM is only for engines L86, LS0, LR0.

I'm satisfied D1943A is correct for my L05 engine. Hope this helps anyone else who may have run across this.

 

[Schurkey]

"HEI" was a radical change in ignition systems when introduced in select vehicles in '74; and "across the line" in '75. All V-8s got the Coil-In-Cap version, although inline 4s and 6s got a separate coil. Eventually, even many of the little guys got coil-in-cap.

When someone says "Without HEI" on our vehicles, what they mean is "without coil-in-cap" HEI. Which is crazy, because so far as I know, every GMT400 built for the North American market got the "small-cap" HEI.

Either ignition module will "work". AC-Delco is not known for letting engineering details escape into public knowledge. What--if any--differences exist between the two will likely never be known; at least not directly from GM/AC-Delco.

There's another web site where 8-pin modules like ours were compared by the GM (not AC-Delco) numbers. Supposedly there's internal timing differences that make one module preferred over the other with the performance enhanced over a certain RPM.

I tried 'em both, couldn't tell a difference. The guy doing the tests seems to be reliable although I'm not thrilled with his methodology. And the aftermarket modules claim to replace BOTH of the GM units. If the ignition timing was actually different between the two GM modules, that would affect emissions and fuel economy--heavily regulated by the EPA.

'Course, I'm too lazy to conduct my own tests. I can therefore neither confirm nor deny that the two modules in that other test are actually different.

The 8-pin module you CAN'T use would be the "Marine" module. It's intended for non-computer applications, therefore it's got an engine-speed-sensing timing-advance curve built-in.

 

[Rain]

I also had seen some info on them having timing differences built in, especially at real high rpm. Thanks for the info also on HEI, most people generally taking that for having the coil in the cap. That had been my impression also before looking into this. Still kind of bugs me that ACDelco shows both ICMs for my engine, and then talking to them, they say oh no, D1943A is the only one. I would think their consumer accessible info would match what he looked up.

Thanks to you and PlayingWithTBI for replying.

 

[PlayingWithTBI]

Still kind of bugs me that ACDelco shows both ICMs for my engine, and then talking to them, they say oh no, D1943A is the only one. I would think their consumer accessible info would match what he looked up.

Yeah, I've been running the D1984A for ~3 years now with no issues.

I seem to remember those ICMs had different "Spark Latency" but I haven't pursued it. Maybe @L31MaxExpress was involved with that? IDK

 

[Rain]

I had figured either would likely be fine. I just wanted to get to the bottom of it because it was bugging me!