Chuck Jones

I've got a perplexing problem. The TT has sat in the garage for over a month on a battery tender. I decided to take it out for a spin and noted that the light was on warning of low gas. I didn't fill it right away and the gas level dropped to below that point where the manual says it won't register miles left to zero...so I did fill it at that point.

I brought it home and parked it. Several days later I went to drive it and it started just fine. I stopped for brekfast and when I came out to start it, it loped as though only firing on 4 cylinders. It ran rough and finally threw a CEL.

I drove it home with the CEL and "Drive to Service" warning displayed on the dash. Afraid to drive it further, I called AAA and had it towed to the indy's shop. The next day I got a call from the Indy who advised that they had put it on a PIWIS and it failed to display any code...and it started and ran just fine after they cleared the CEL. Since I had no way to get down to the shop, I asked them to drive it back to my house and drop it off. The indy drove it back and said it ran just fine.


The next day, I got in and it started fine...but after I stopped at an appointment and came out, it started that damn loping again and missing on a couple cylinders. I drove back to the indy and put it on the computer again. This time it read out misfires on cylinders 5, 6 and 3....but smoothed out again and ran just fine all the way home. I called Kevin at UMW and he suggested trying a new MAF...ordered and installed it several days later. The next day it ran ok for a while, but then the same damn thing happened again...threw a CEL and loped as though missing on several cylinders....verified again by the OBD readout. I just went out a few minutes ago and fired it up...outside temp is 57 degrees, just rained so there's humidity in the air...and it ran just fine but I didn't drive it anywhere.

So at this point I have some sort of intermittent problem that's causing several cylinders to misfire, but not always the same cylinders...but if I run it for a while, it sometimes just quits loping and smooths out, but the CEL will stay on....but if I stop and start it again sometimes the misfire comes back. On other occasions, if it's acting up and I stop, turn off the ignition and wait a minute, then turn it back on, it runs as though there's nothing wrong. The problem is inconsistent and perplexing.

Any thoughts, suggestions, or theories would be immensly appreciated.

Forgot to put in some info...car has 42K miles on it. Changed plugs at 30K but not coil packs..inspected and looked good. Misfires are occuring on different banks. Does that suggest trouble upstream of coil packs>? Fuel pump? dunno.

dantzig

When I had an intermittent problem like this, it turned out to be a bad coil pack. But it was more consistent than yours. 42k may be time to replace the coil packs anyway.

Chuck Jones

The trouble I'm having is that the intermittent problem appears on different cylinders....I could see one coil pack going bad, but not different ones on different banks...although cylinders 5 and 6 seem to come up more frequently...and they're on the same bank.

Macster

Misfires on various cylinders both banks. New MAF. Lots of rain. Humid. I'm going with coil packs.

There are some with experience with these cars who advise replacing the coil packs at 30K miles just on general preventative maintenance principles.

Might be something to that.

Misfires can be caused by coil packs, fuel supply problems, VarioCam problems, and bad MAF, or bad plugs to name most of the possible causes.

You've replaced the MAF. You just had the plugs replaced and assume the work done right and the coil packs connected securely, etc? (Last thing touched is always suspect.)

You filled tank with fuel.

It has been wet, damp, and likely cold (we had some cold rain through here the last couple of days off/on. At lunch today, standing outside, I thought I was back in the middle of winter. Well, what passes for winter here in the SF bay area.

Absent any other error codes other than misfire error codes, and no other symptoms, I'm going with coil packs.

Added: A randomness to the misfires is actually some extra weight towards it being coil packs.

Sincerely,

Macster.

dantzig

Yeah, that's what I meant by mine being more consistent than yours. Mine was always the same cylinder Sorry I don't have anything more valuable to add.

Land Jet

Chuck, you might consider changing your fuel filter too since you ran the gas down to nothing, maybe you sucked up some tank residue that could be contributing to the problem. But I also think that coil packs are the main problem. Didn't any of the read-outs give you some indication of the problem area beside which plugs were misfiring? Do you ever run Techron through your fuel system?

kendo

I had this on my 993 and it was dodgy injector... it would affect the specific cylinder the injector was attached to intermittently giving misfire on that 1 cylinder but would also throw out 3-4 cylinders when engine started from hot. Weird because only 1 injector faulty.... I had the injector replaced and it was perfect from then on. The 993 was sold a short while ago, agreed to buy 996tt which I hope to pick up next week, can't wait. Good luck with fixing your car.

BostonDuce

I would change the fuel filter first. Then try fuel injector cleaner.

Throw money at SWAG's in order of expense --cheapest first.

Read Kevin's last post in Mac's "oil and plug change thread". Your misfire codes are for the cylinders he says DON't usually eat the CP's.

BD

Bob M

Chuck, I had the same intermittent misfire on the left cylinder bank. I tried everything – plugs, MAF, Coil packs, O2 sensors and other things but nothing solved the problem. I was beginning to think I had a variocam issue. The culprit turned out to be a broken cam solenoid bracket, which allowed the solenoid to move slightly, especially under acceleration. It cost big bucks to discover that it was only a cheap part. I would recommend you see if this might be the cause of your problem before you go to the expense of replacing these other costly parts. Opportunity again to thank Tony Callas, Chris Walrod and Robin Sun for their help in getting this thing figured out for me – thanks guys!!!

Bob M

I should have added that there were others on RL that had the same problem related to the cracked bracket. Good luck!

Bob

Kevin

My recent advice is check and replace the fuel pump. Because the misfires only occur right after the car is started. After the car is running, nothing happens..

The fuel line in the tank is leaking, air is getting in the line.

We are getting multiple cylinder and BOTH bank misfires at random. The CEL have flashed and cleared up till now. Usual CP and plug misfires happen from 4000 to 5000 RPM's..

Chuck Jones

Great advice guys, and much of what I've been getting seems very logical and practical...and I will approach this as Boston so adroitly stated..."SWAGS in order of expense". Logic might seem to point to a fuel issue because of the on again/off again nature of the onset of the problem....usually right after I've run it with no issues, then turn off the engine, and upon restart, the feel of at least two cylinders not firing. If nothing else, I've got a good extra MAF!!

I'll keep you posted as I go thru the exercise of chasing it down. What still perplexes me is the fact that on at least two occasions even with the CEL on, and after I had it towed to the shop because I didn't want to risk driving it, when they fired it up and put it on the OBD reader, there were NO FREAKIN CODES!!....and it ran just fine. How could it throw a CEL after misfiring but have nothing stored in the computer??? I don't understand that.

Macster

Apparently, a misfire error is not deemed to be sticky or of a persistent classification.

Upon engine restart the slate is wiped clean (at least for this error, while on the other hand, P0430 is damned sticky...) the error codes are erased and in doing so this extinquishes the CEL.

Misfire detection is an ongoing process. While the engine is running the engine controller is constantly checking for misfires by measuring the acceleration imparted to the flywheel by every cylinder power stroke. If the amount of acceleration is too low (or too high) and if after sufficient number of back to back events have been detected to alarm the engine controller a potential for misfires is present, then if enough misfire events occur a misfire error is flagged, recorded, and the check engine light lit.

If the misfire events stop before the misfire error threshold is reached the alarm is canceled and the looking for another series of qualifying events begins. No record of there having been a potential misfire qualifying event is recorded or remembered.

Misfires by definition are transistory though of course can not be if the root cause is present and remains in effect. We've read reports of a flashing CEL (misfire than can damage the converter) and about the time the driver can react and get the car over the CEL no longer flashing.

Even if the CEL not flashing but steady on the act of turning off the engine this resets the continuous misfire monitor testing.

Furthermore, if the engine left off long enough the next engine start will have the engine so cold the engine controller will be running in open loop mode and there is limited checking for any emissions related errors. Misfires that do not put the converter at risk are probably not checked for during this warm up phase. Misfires that do put the engine controller at risk can be checked for and the CEL flashed.

Sincerely,

Macster.

Macster

Oh, new info regarding no codes. If the fuel level low, too low, and misfires are detected error codes are not recorded. The assumption is by Porsche the misfires are due to low fuel level. Makes sense. The fuel tank will get topped up and if the misfires are due to some other cause the owner will know soon enough.

Sincerely,

Macster.

jpflip

Chuck. You should drive around with the durametric connected and record some parameter related to your problem until you got the fault.... ex.: cam angles, ignition cylinder#....