What is causing my MSD coil to short thorugh its case?

[cda951]

You are not experiencing detonation or pinging, this is an abnormal combustion event which occurs AFTER the main spark event, and only happens when the engine is at or near full load---not really possible while blipping the throttle in neutral or even during light-load acceleration.

Please read this article, I have posted it many times to this and other automotive forums, it is one of the best I've read on the subject, and it used to be linked from @chris white 's 944 Enhancement website which seems to be down:

http://www.contactmagazine.com/Issue54/ ... asics.html

It seems like you have a defective ignition coil, with an unusual failure (I have had MSD Blaster 8222 coils in 4 or 5 of my old cars, have been great), but should switch back to the stock original coil if you still have it. Both my '86 951 and '90 944S2 have functional original coils (I use a wasted spark coil for the 951 due to increased boost and a larger turbo), but the replacement aftermarket Bosch coils are junk.

[Aaron_N]

Permatune makes a kit that costs $800-ish that allows you to use aftermarket coils with some performance gains. It was designed as an (expensive) solution to the problem of aftermarket coils not working properly and OE coils being expensive and hard to find. Admittedly the cost doesn't make sense unless you are a racer looking for a few HP.

[Jacquiles]

I made the same assumption and put in the MSD coil in 2020 based on it being on Lindseys product list. Haven't seen the Arcing issue, but Given the DME electrical load issue, I'm going to grab a Bosch and see how it compares.
Note - I bought one on Amazon (Bosch Part Number 0221118322) where it was about 1/3 the price of the usual places with 944.x part numbers.

Porsche is very skilled at taking Bosch parts, putting them in Porsche boxes, and charging 3 times as much. That said, I just poked around and it looks like the factory coil is actually cheaper than the seemingly identical Bosch? Pelican for example sell the factory one for $210 and the Bosch one for $246.

Rogue Tuning did some o-scope tests a while back on these coils and concluded they drew more current than the factory coil, which can lead to an over-heated ignition driver transistor and resulting transistor and/or solder joint failures in the DME. He was able to alter the dwell (charge-up) time in the DME maps to reduce the draw, but for most of us, those coils just add stress to the DME without any appreciable benefit. On a turbo, like yours, a stronger ignition might be warranted if you are pushing the boost, etc., but if so you are better off getting an ignition box like the MSD 6A and matching MSD coil. I did that for years. That will take the stress off the DME and make sure you are charging the coil as intended. For an N/A 944, I think aftermarket coils are just a solution in search of a problem.

I meant to update yall much sooner, but got busy towards the end of school with engineering classes. I swapped the MSD with a new bosch coil and it has been working perfect. No more arcing! I may never know why the MSD coil did that, but maybe it had something to do with the fact i have the MAF kit installed, maybe dwell times or something related to spark were adjusted from the factory settings with the new chip and could have a relation through that?? Who knows.

[Tom]

I made the same assumption and put in the MSD coil in 2020 based on it being on Lindseys product list. Haven't seen the Arcing issue, but Given the DME electrical load issue, I'm going to grab a Bosch and see how it compares.
Note - I bought one on Amazon (Bosch Part Number 0221118322) where it was about 1/3 the price of the usual places with 944.x part numbers.

Porsche is very skilled at taking Bosch parts, putting them in Porsche boxes, and charging 3 times as much. That said, I just poked around and it looks like the factory coil is actually cheaper than the seemingly identical Bosch? Pelican for example sell the factory one for $210 and the Bosch one for $246.

Rogue Tuning did some o-scope tests a while back on these coils and concluded they drew more current than the factory coil, which can lead to an over-heated ignition driver transistor and resulting transistor and/or solder joint failures in the DME. He was able to alter the dwell (charge-up) time in the DME maps to reduce the draw, but for most of us, those coils just add stress to the DME without any appreciable benefit. On a turbo, like yours, a stronger ignition might be warranted if you are pushing the boost, etc., but if so you are better off getting an ignition box like the MSD 6A and matching MSD coil. I did that for years. That will take the stress off the DME and make sure you are charging the coil as intended. For an N/A 944, I think aftermarket coils are just a solution in search of a problem.

I meant to update yall much sooner, but got busy towards the end of school with engineering classes. I swapped the MSD with a new bosch coil and it has been working perfect. No more arcing! I may never know why the MSD coil did that, but maybe it had something to do with the fact i have the MAF kit installed, maybe dwell times or something related to spark were adjusted from the factory settings with the new chip and could have a relation through that?? Who knows.

Glad the new coil worked! My guess is that it was just a quality issue with the MSD coil. Their reputation proceeds them...