Hei module fried?

So I decided to try a new Accel module in my ignition amp on my 88 XJS. Removed working GM one, cleaned off old grease, put in new one.

Drove 2 miles, and it stalled. Waited 15 secs and it started and drove about 100 yards, and then stalled again. Managed to get it home after four restarts.

Took it apart, I’m an idiot, FORGOT to put thermal paste on! Did I fry it?

I would change it regardless, it costs nothing.

The Accel module is $45! I ordered it thru Amazon, maybe I could send it back defective.
I’ll put some thermal grease on it tomorrow, it either works or it doesn’t?

And why not the GM module? It costs $10… That’s what I have put in my car and had no problems. Got a second one as well that lives in my tool box just in case…

$10? I could not find the GM Module for under $30.

I heard the Accel “Performance” was slightly better, I was curious to see if it actually helped deliver better spark (for starting and high rpm) And this allowed me to keep the GM one as a backup.

The stock GM HEI delivers a spark good enough for everything short of all out race engines, why do you think you need a hotter spark?

Curious, and I had an extra $45 to burn :slight_smile:

Over the years there has been some speculation about the ignition module not being well grounded after replacement. Specifically, some have a distinct grounding tab connected to one of the mounting holes and others don’t. Might be worth checking into. Here’s one thread, but I’m sure there are others

Would poor grounding fry a new module? I don’t know.


tried the accel years ago, never ran right. moved on to other things and forgot all about it. before moving on, I was looking at rpm’s, the jag fires 50% more times than the v-8 so maybe an issue there? as I said, stuck the gm back in and moved on but maybe others will have input addressing the shorter time between firing.

When mine died installed an Eclin from NAPA for about $24.00.
Had bought a new unit but returned it as there was no diode installed. Reported this previously.
Rebuilt old unit and made a back shield from tin SS shim stock to reflect heat. Has been in stalled since July 2016.

New one with out diode is on the left.

The GM module is also designed for a V8, so that doesn’t make sense.

I’ve decided to exchange the Accel and try again, but this time I am buying some quality thermal grease used for CPU’s with an 8 year life guarantee, instead of the unknown packet that comes with it.

Also, my ground for the module is hooked up to the left screw, by the W/G connection. Surely either one will work?

Not sure how you figure that. Oh, a V12??

Interesting. but, as I get it. It merely makes and breaks the Ground leg to the coil, Only by solid state electronics, and not electro mechanical as in old tech points and condenser.

It is pretty much accepted, that electronic devices abhor heat. Most failures heat related !!!

Not that I need one, but the thought of a device to bench test the modules has occurred to me. Spare distributor, coil and a motor to drive it??? Use the heat gun for testing, or swipe the Ms’s hair dryer…

Musing done…


I’m pretty sure the GM module that is in our V12’s is the same used in GM V8’s in the 70s-80s. They didn’t make one specifically for Jaguar.

Carl, Greg,
Someone on Jag-Lovers posted a procedure to test that module years ago. I don’t have it handy, but I know that it exists because I used it. If you search the archives you should find it.


“if” the performance at higher rpms is the same or better. an aftermarket module may of been designed better in one area but lost something in another.

Thanks Paul, I’ve used it before.

With this one, I decided to simply exchange and let Amazon take the hit. I’m sure Jeff Bezos will still be alright. :wink:

That totally makes sense. I just am curious to try the Accel, reading the archives, I saw plenty of good reviews.

If your problem continues after amp replacement, I’d suggest Ohm-ing the coils just after failure. On a couple of different cars I’ve had coils that went out with heat soak. They’d start, but sound sick trying to reach anything above 2K rpm… bllluuruuruurrrrggg… just wouldn’t do it.

The advantage of buying an aftermarket HEI module is knowing what you’re getting. Not al GM HEI modules are made the same apparently. Many of the cheaper ones have an amperage limit that starts showing it’s ugly face around 4500rpm – and that’s splitting the spark on 8 cyls … not even 12.

Yeah… the heat sink compound will definitely help. Also-check your AB14 module’s suppression cap for being shorted internally to ground.


Paul K.

Thanks, but I know it was the Accel overheating due to no thermal grease. The GM module I pulled out has worked perfectly for 6 months. It’s back in now. I’ll try the Accel again WITH grease over the holiday next week, after plenty of turkey.

That new one has a diode, it’s just shaped differently. It’s that black blob connected to the mounting post.