What's that smell? Wait, and why isn't my car running?!

[Tremelune]

Is it possible that this thing needs a proper heat sink that isn't present under my seat? I found a photo of what it looks like installed in a 993, and that whole metal bracket might be acting as a heat sink. It just seems unlikely, since this thing has been under my seat for a thousand miles. I wish I remembered how it was installed...Maybe it was using my whole floor as a heat sink? I still dunno. It's been fine like this for a few hundred miles at least.

What are 3.6 swappers doing with the ignition module(s)?

[prschmn]

Yup there were dual output modules used in 993s-not 964s
I'd be checking wiring between that and the coils-something going to ground?
And then check both coils-ohm them out carefully.
Heat is a sure sign of excessive current draw.

[prschmn]

And yes it needs the heat sink-they pass a fair amount of current and do get warm.

[Sboxin]

"What are 3.6 swappers doing with the ignition module(s)?"

We have a 3.6L conversion 1992 964 - it has 2 ignition modules located on a bracket that also
holds the 2 coils in the engine compartment driver's side -

EDIT: I just took a look at the Porsche parts pdf and the 993 only has one ignition module and
one combined dual coil - - is that what you have in your car?? The module seems to be mounted on a bracket with the coils - not under the seat.
You might post this question on the 993 Forum . . .

Regards,

[Tremelune]

I bought a factory heat sink and some thermal grease...My current plan is to bolt the little heatsink on with some screws and thermal grease, then attach it to the painted metal floor with thermal paste. This is...more experimentation than I'd like.

I've got a [url=https://rennlist.com/forums/993-forum/1010758-i-just-can-t-get-this-thing-to-spark.html]thread on the Rennlist 993 forum[/img] in the hopes of finding more specific stuff there, but some of my car is 3.2 and some is 3.6, sooo...

I'm doing some modest tests on my coils. According to this thread, I want 0.7Ω for the primaries and 8200Ω for the scondaries. I'm also not too sure these measurements are super accurate, since it would sometimes fluctuate wildly, but these numbers were the most consistent/stable...and seem fine:

Coil 1
Across posts 15 to 1: 0.7Ω
Across posts 15 to 4: 8.16kΩ

Coil 2
Across posts 15 to 1: 0.8Ω
Across posts 15 to 4: 8.14kΩ

The terminal wires don't look bad, but they don't look great, so I might redo them.

[pmax]

More suggestions, I would check or replace the coils and alternator voltage too in case they are out of spec.

[Tremelune]

I was waiting on parts and I couldn't just leave those janky wires there, so I redid them. I tried to find some 90-degree eyelet lugs, but I couldn't find any that would fit posts this small—at least not without waiting a week and paying $5 in shipping. I just used regular ring terminals and bent them. I used a bunch of shrinkwrap in the hopes that it will act well as stress relief in these tight quarters. Also got a chance to try out my Techflex split sleeving...

I found that both 15 posts came from the same wire that was spliced in the engine bay. Not sure if that's normal or what...There were definitely a few cracks in brittle installation in the wires, though they seemed to improve in condition towards the firewall, so I didn't tear anything out—just cut the wires near the fan and ran new 14awg to the posts. A splash of Fluid Film will ensure the posts stay clean.

[Tremelune]

I believe I have attained success. I slapped a biggass heatsink on the new ignition module (cheap knockoff), joined together with Thermaltake TG-7 thermal grease (shoutout to my overclocking days) and some bolts. The car started up, the heatsink quickly warmed. During an hour drive, the ignition module temps stayed steady below 70°C (see underseat thermal pic), and the car ran brilliantly.

I'm not sure why the original module lasted as long as it did with no heatsink (it was a factory Bosch part), but as long as the car is running steady, I'm inclined not to worry about it.

[pampadori]

This was an interesting read and i'm glad you got it figured out in the end!
I would like to pose a question though. From my prior days working on honda motorcycles from the 70's, I recall that replacement ignition coils were available in different ohms. If you used the wrong ohm coil you could end up with other electrical items being taken out by it. Too much or too little resistance caused problems.
So does the ignition module and the coils need to be matched here as well? Are the coils you're using the right "spec" for the rest of the setup? I assume yours are since the test you ran showed them to be in spec per the book.

BTW that heat imagine picture is great! If i had something like that I'd just walk around using it on random things and would get little else done. I'm easily amused i guess!

[Tremelune]

Yup, if the ignition coils are struggling, they can stress other aspects of the system. I was prepared to replace the entire ignition system from the plugs to the computer if I had to, but at $25 per ignition module and no obvious issue elsewhere, it seems like a good idea to just give it a whirl with a proper heatsink and see what happened long-term. Both my ignition coils and module are to factory specs (as far as I know).

The thermal camera is fun. Sometimes I can spy on critters in the yard...

[fallingat120mph]

Originally Posted by Tremelune

I believe I have attained success. I slapped a biggass heatsink on the new ignition module (cheap knockoff), joined together with Thermaltake TG-7 thermal grease (shoutout to my overclocking days) and some bolts. The car started up, the heatsink quickly warmed. During an hour drive, the ignition module temps stayed steady below 70°C (see underseat thermal pic), and the car ran brilliantly.

I'm not sure why the original module lasted as long as it did with no heatsink (it was a factory Bosch part), but as long as the car is running steady, I'm inclined not to worry about it.

Reviving an oldie...


Wondering how this worked out for you or anyone else. Using a 993 ignition module and think my heat sink is too small...the modules do get very hot.


Erik

[Tremelune]

I had no issues with the car after I moved to California and ran it up to Big Bear a bunch of times...I sold it after a year, so I can't speak to the longevity, but I had no issues with that module after adding the heatsink.

The stock setup is using the back metal bracket and chassis as a giant heatsink, but if yours is under the seat that's not much of an option unless you attach it to the floor...Giant amplifier heatsink or desktop CPU heatsink with 12V fan.

70°C seems too hot to me for electornics, but it did work!

[fallingat120mph]

Originally Posted by Tremelune

I had no issues with the car after I moved to California and ran it up to Big Bear a bunch of times...I sold it after a year, so I can't speak to the longevity, but I had no issues with that module after adding the heatsink.

The stock setup is using the back metal bracket and chassis as a giant heatsink, but if yours is under the seat that's not much of an option unless you attach it to the floor...Giant amplifier heatsink or desktop CPU heatsink with 12V fan.

70°C seems too hot to me for electornics, but it did work!

I am looking at an 6x6in or 8x8in to mount under the seat. Currently have my module in the engine bay on modified 964 heat sink and think it's way too small. Just burnt another one out yesterday.

So, going to try a larger heat sink as I think that's where my problem lies.

I didn't realize just how hot a single 993 ignition module gets driving a 964 distributor. Car runs like a top when on the ope road, but fear my issue lies with the ignition module is getting too hot.


Can't thank you enough for your response! Any other input you have is greatly appreciated...I am learning as I go with this new 3.4 build.


Again, thank you!
Erik

[Mr. Merk]

This thread is what made me think you might've had ICM issues

[fallingat120mph]

Originally Posted by Mr. Merk

This thread is what made me think you might've had ICM issues

First thing I thought.

Turns out it was most likely the CHT (per another thread) BUT...my module did go out after trying to get things running here on the back roads.

The heat sink in the engine bay I feel was trimmed down too small and the location was making things too hot.

Just received a new larger piece of aluminum and will mount under the seat and see how that goes.

DME, CHT and ignition module are now in my glovebox as spares



Erik