Adrienne

I have an intermittent hesitation problem. It is most pronounced when engine is cold, and then again when the engine is very hot. Unfortunately for diagnostics, it does not happen all the time. It is generally occuring between 3-4k rpm when under acceleration. It has thrown the CEL twice, with codes for misfire on cylinder 6, and voltage irregularities. Any ideas? So far we have tried the DME relay, fuel injector, plug wires, and ECU. None have worked. Our next step is MAF sensor, but it seems odd that I'm only getting codes for cylinder 6.

Sure seems like a wiring issue to me. The wiring harness was replaced 3 years ago with the recall. I had the engine rebuilt and it started just after that. I'm thinking maybe a wire is crimped, but they said they checked for that already.

I appreciate any ideas you guys may have.

Thanks!

Dan V

What about the distributors? Seems like a logical place to check -- you probably did but just didn't mention it yet.

viperbob

The problem with these things is that you have to look at everything to start narrowing it down. Just take time and a manual. Another source of misfires is the DMF. But if you are only getting cylinder #6 it is less likely...

mborkow

the problem started directly after the rebuild? if that is the case, take it to whomever did the rebuild and make them figure out, right?

tam993

was the #6 spark plug ever changed.... normally people don't .
unless the engine is out.

Adrienne

All good ideas.

Viperbob - yep, that's what we are doing. We started with the DME relay, then worked up from there - injector, plug wires, ECU. We replaced the distributor caps & rotors, ignition wires, and all plugs with the rebuild. I did the RS LWF conversion also (which by the way is a very close 2nd to upgrading suspension...wow!! What a great mod!!) so it's not the DMF causing misfires.

It's at the shop that did the rebuild, and although this did start happening about a week after the rebuild, it's still unclear if it is related or just coincidence. They are pulling out their hair trying to figure it out. We got a good lead on some ideas from the stealer, I mean, dealer and a few others shops across the country. It could be a problem with the positive battery lead, as the dealer said they had that problem with a few cars.

I'll post once we figure out what it is. But if you guys have any other ideas or have had similar problems, please post them. My wallet sure would appreciate it!!

Davies

I know the elusive misfire search only too well...I had a detonation issue and pulled my hair out going through all of the same possible culprits as you have, and it ended up being a bad plug wire arcing off the one next to it - causing a rogue spark. (You could see it with the engine running in the dark...) Sometimes it's something really simple.

You say you get a little hesitation, so I'm assuming no detonation/knocking. I suppose there's no harm in swapping out the battery leads, but I'm guessing the hesitation from momentary electrical power loss probably wouldn't throw a misfire code, especially for the same cylinder everytime(?). Have you tried a new set of plugs just for cylinder #6? I know I'm reaching here, but are the plugs screwed in tight? Spark plug caps/wires seated properly? You said it happened right after the rebuild, during which the plugs were replaced, so it's worth a look.

Good luck. I know how frustrating this can be!

c993k

Do you notice it more when there's moisture or high humidity in the air?
Chris

tam993

I had that wire arching problem with my 88 Carrera, they were 20 yrs old.
only way I found it was to spray the wires with water out of a spray bottle in the garage in dim light.
only missed every now and again, tough to find.

Adrienne

Thanks for all your help and thoughtful suggestions. You'll never guess what it was.

It was due to the positive battery lead. Through discussions with the local Porsche dealer and other shops around the US, we heard about this rare problem. Oh goody, I just love when my car does something rare.

I was getting codes for supply voltage, misfire cylinder 6, and injector circuit cylinder 6.

So, the resolution:
My mechanic cut the main accessory wires 3 inches up from the battery terminal, re-installed new connectors, and re-soldered the positive battery terminal.

This problem is very hard to trace, as the codes are erroneous and point to other issues. It was no small cost finding this problem, as we checked EVERYTHING related to cylinder 6, and then started from scratch again. Apparently a very small number of you will thank me later when this happens to you, as it occurs on 993s very rarely. Consider this money in the bank.