Danieldd

Last week when I acquired my S4 (see thread: My Impulse Buy - 1987 S4 ), the engine was running extremely rough to the point where I had it towed home. After running a compression test and vacuum test, I proceeded further and checked the resistance of all the plug wires. They all were approximately 4.1K. Next, I took a timing light and checked for spark on each of the 8 plug wires and found 4 to have no spark, which I then isolated it to the driver's side distributor cap. Pulled the distributor cap and it checked good and was about to pull the rotor button when I looked to my right and saw this:




So, I removed the coil. Looked like it puked on the car..



Then, I removed the protective cap on the coil and found this:



Never seen this before, in any type of car. I thought these coils didn't go bad. Oh well, got one on order and should be here Monday. Just thought I would share will everyone - maybe it will help others.

88porsche928

what did you use to test that all the spark plugs work? I am paranoid that one of my spark plugs might not be working or a fuel injector is clogged.

blown 87

I have seen it before, a couple of things can happen to cause that, the key left on in a points type car, or a internal short in the coil causing it to pull to many amps.
I am willing to bet that there are other failure modes also.

Danieldd

I had replaced all my spark plugs with new ones, so I ruled them out. To test that each spark plug wire was getting fire/spark, I took my inductive timing light and hooked to each plug wire while the engine was running. If I got a flash from the timing light, then I knew that wire was getting the necessary spark.

Best I can tell you is to use an ohm meter on your wires and make sure they are within spec (whatever that is), make sure they are getting spark and insure your spark plugs are good. If you have a potential fuel injector problem, then I will defer to someone else on this forum that may have a more comprehensive test than I would be able to suggest..

Imo000

Yup, all the cylinder style coils are oil filled. As a temprary measure, you can use any other coil that looks like this but some, like the Accell ones, will produce a weaker spark so there will be some loss of power but the engine will run fine. At least that was my experience with an '83 16V.

WallyP

Porsche flatly says that you should never use any ignition coil other than the specific one for your 928...

Imo000

While the egnine is running, start pulling each spark plug boot and find the oen that doesn't make a difference. Then pull that plug and have a look. If it looks brand new, the injector is not firing. If it looks normal, the problem is the plug, evne new ones are sometimes bad, or the plug boot.

Anothe rway to find the missfiring cylinder is with an infrared teperature gun. The one not firing will be a lot cooler than the others. Do this before the manifold gets heat soaked.

gbgastowers

I thought they were wax filled. Gunar

Danieldd

Hmmm. When I pried it off the top of the coil, it had the consistency of wax, so you may be correct..

tmpusfugit

There is some possibility that the coil potting materials contain dioxin/pcb components. The original EPA plan was to outlaw the use of materials containing dixon after 1978, but that was not 100% implemented on schedule. Use caution with any old electrical potting materials....just to be safe....pcb's were found in motors, transformers, large capacitors, coils, etc....

Landseer

Just general FYI, 944 coils match the part no. for 32V 928 coils.

In a pinch it might help. At least it helped us once.

dogleg

that works great on a 4 or 6 cylinder engine, but one plug off on a smooth v8 at idle is not that easy to hear.not sure its safe to do either for the rest of the ht electrical system.

Danieldd

Good information. I played it safe and used nitrile gloves, and BTW, I didn't EAT any of it..

Imo000

I know but two cylinders not firing is easy to hear. And since one is already out, by removing another one, will tell you if that cylinder is firing or not. Stop when you get to teh one that doesn't make a difference. I did this with my own car when an injector failed.