Hi,
I'm about to replace my ignition coils on my 1990 964 C4. Does anyone have any advice? How easy is this DIY? Do I need to disconnect battery terminal for this job?

In the process of replacing the coils, what other ignition related parts should inspect? Thanks!

 

(Unlike the starter) the spark parts of the ignition are pretty safely dead if the key's not in the ignition.

The coils, distributor caps and rotors all lend themselves to simultaneous replacement. It's a 'better safe than sorry' with their change frequency.

The next level of expense/PITA parts replacement would be plugs and spark plug wires. This is a quantum leap of time & commitment to disassembly, over the prior parts. If you don't have the money, time, or pressing need, I wouldn't sweat these if coils are on your mind...

Have fun!

 

The replacement is pretty straight forward. You will probably want to remove the rear fuse box cover, for better access. Then the coil covers, then the coils. The working space is a little tight. Careful not to drop the little nuts that hold the wires. I always like to disconnect the negative battery cable, when working on anything electrical.

 

Jamie wrote a good DIY. Unfortunately, his photos are missing.

https://rennlist.com/forums/964-1989...ug-cables.html

 

Should I replace the ignition module and the wire that attaches to the module as well? Are those sold separately or packaged with the coil when purchased?

 

They don't come with the coils. I have had the IM's fail in my 944S2 (same unit I think) stranding me. So while I don't think you need to replace them per se - I'd have one on hand - with your DME relay back up unit. : )

Process of re and re'ing the coils isn't too bad. LOTS of little nuts and washers - so be careful and have your long handled magnet handy.

I think I had to remove the blower fan for more space. But maybe I was replacing that anyway? I remember having lots of space with the blower out.

RK

 

On this topic, what are the best coils to get now? I recall reading that the Bosch coils of late were crap.

 

It can be done without removing the blower fan but it's better to give yourself less hassle and more room by removing it. If you do this you do not have to remove the fuse cover.
+1 on doing the caps and rotors at the same time.

 

I also want to replace the connectors to the ignition module. Does anyone know where to find these wire connectors? I've searched the web to no avail. My last resort would be the local Porsche dealership. And I know they will charge me an "arm and a leg" for it.

 

The connectors are part of the engine wire harness. Not sure if they are available separately. The harnesses are not cheap and it would be a lot of labor to replace. What makes you want to replace the connectors?

dcAuto has a picture of the wire harness = http://dcauto.gotdns.com/illustration/index/932335394

No affiliations.

 

I've been logging code 41 and 34 and I've been having erractic idling problem when engine is cold. Someone in Rennlist suggested to check coils by disconnecting them one at a time. When I disconnected the aft Ignition Module connector (leaving fwd connector installed), I would hear a ping or misfire and when I switch the same connector to the aft IM the same ping and misfire occurs. On the otherhand, the aft IM connector does not show pinging or misfires when I switch to either fwd or aft IM. Therefore I think I isolated the problem to this fwd IM connector. Am I accurate in my conclusion or am I over simplifying this coil test? Any info is very much appreciated.

This maybe good for another topic to post. Thanks.

 

RNR247, you are close. the aft connector is your problem. now it could be your coil or ignition wires or plug. you need to do one more test and that is switching the ignition coil cables, that way you can see if the coil is the culprit or the wires/plugs.

 

You mean switch the ignition coil cables from the "distributor side" or "coil side"? And perform the same steps as switching the IM connectors (one at a time)?

I apologize. I didn't do too well in Electrical 101.

 

You can switch the coil wires at either end. The test will work for you. My bet is you have a bad coil or bad spark plug wires. The connectors you swapped before are low voltage (12v) so I doubt they would cause misfire. Its more likely that you have a leak in the high voltage circuit somewhere (coils, cap rotor, spark plug wires).

 

My suspect has always been the coils, since cap/rotor was just replaced and plugs/wires were replaced at 3K miles ago (major service).

Question: Can a bad coil cause erratic idle when engine is cold?