Misfire
 

I thought I would run this by the congregation. I recently picked up an OBD2 reader because I got the CE light. It showed misfire codes for cylinders 1,3,6,4. I have already replaced both rotor and caps, all ignition wires, has the second distributor belt replaced after a failure that cooked one dizzy cap. I'm scheduled to have my guy look at it, but he can't get to me for at least a week. While he wasn't able to talk because the shop was busy, he did say it was significant b/c the faults were all on one side (or something to that effect). Can anyone enlighten me as to what he meant, and what is the likely source of this problem. The car is running roughly at idle, and I don't think I should drive it until I figure out the problem.
TIA

Do you think the misfire codes happen at idle? My car threw one the other day while stopped at a light. My DMF is failing, I can hear it knocking and rattling about, especially when hot, when I shut it off. At idle the failing DMF causes the engine to run erratic, the ECU thinks this is a misfire.

Hmmm... The clutch etc was replaced about 40k miles ago and I haven't had any problems with noisy drivetrain related parts. But I will listen again tomorrow. Thanks.

When my CEL comes on it's either the SAI or a "Random Misfire" - my car is running a bit rough when idling as well but I think it's caused by the engine mounts.

It's not clear to me if the caps, rotors, wires, etc. were changed before or after the CEL appeared.

If before, it could be that some of the plug wires were misrouted. I got a CEL after replacing the caps and rotors when I got just two of the wires pluged into the wrong holes in the upper distributor. Once that was corrected it works fine now.

Good luck.

Dan, I can't remember if the black covers on our distributor caps have cylinder numbers marked into them, but if they don't, I've taken pics of my caps and labelled each with the spark plug wire location.

http://edelweiss.smugmug.com/Cars/Po...tor-Cap-XL.jpg

A few years ago I was consistantly getting random misfire codes when at idle. I replaced wires, caps, rotors, and plugs and still got the random misfire codes. When my clutch started to slip at 50k mi I replaced it with a RS LWF setup. 10k mi and 3 years later I have yet to get another random misfire code. I believe the culprit was a failing dual mass flywheel.

Cylinders 123 are on the driver side, 456 are on the passenger side, so if you have 1, 3, 4, 6 misfire, it is 2 on each side. If it is a single cylinder every/most times, I would think it is ignition wires or plugs. if it is inconsistent as to which cylinder[s] then that points to DMF.

What brand of belts are you using?

I had the same issue and it was my flywheel at 65k miles.

Alex,

Oh boy--that's a keeper!! Actually I did mark the wires with a Sharpie which promptly rubbed off when I failed to clean the oily stuff off first.

Your picture confirms excactly my miswiring--I-5 and I-3 were swhtched giving me a cylinder 5 misfire.

Thanks so much!! Won't use it for 30K more miles but priceless. :thumbup:

Excellent suggestion.

FWIW, there should be a decal with the layout of the dist. caps and the plug wire locations on the left wall of the engine compartment. It will have the layout just like Alex's photo.

Well I took the pic more for cable routing than anything else.

The ignition cables lengths are such that you need to route them as shown. Angling the boots radially outwards like on distributors of past when you had tons of room in an engine compartment won't work in our case.

I tend to record/store a lot of information. Just right click and save-as to your Porsche folder for future use and less head scratching :D.

Here are some close-ups of each distributor cap (BTW, I can only assume that is factory routing as the caps and wires were still original)...
http://edelweiss.smugmug.com/Cars/Po...-Primary-L.jpg

http://edelweiss.smugmug.com/Cars/Po...econdary-L.jpg

And my new Beru wires. I still have to check to see if it looks like the OEM routing...
http://edelweiss.smugmug.com/Cars/Po...ssor-Cap-L.jpg

Bill, I once asked why factory or aftermarket belts would make a difference and someone tried to explain it as well as provided a link to a thread with an explanation. I raised my eyebrow and I still don't buy it.

Lets assume we don't need engine cooling and that I am running on the reserve capacity of the battery, ie, both belts broken. How does a cooling fan or alternator belt have anything to do with ignition misfires?

I must have missed something very obvious which when it is...you usually miss it.

The issue is not the lack of belts, but the wrong belt size being used. It skips at certain rpms, makes the DMF jump and the DME detects it as a misfire, even though there is no really a missfire. It acts just like a failing DMF. That's how a cooling fan or alternator belt has anything to do with ignition misfires...

It happened to me and I was able to fix not only my car, but 3 other friends 993's having the same symptoms by just switching from Continental belts to OEM Porsche belts. I documented it all here on different posts.

To the O.P. Before you invest anymore time and energy on this, make sure that your belts are OEM Porsche belts.