X51

Hi all - been about 18 months since I left 996 land for 997 land. I still miss the camaraderie of this bunch, so I troll occasionally to see what's up.

A friend of mine and I were at lunch today and he's got a 2004 C4S. Under hard acceleration north of 3500 RPM his CEL light comes on and if he accelerates hard again it starts to flash. He's had it in to be looked at, but the techs are still researching the cause. The diagnostic readout indicates a misfire in cylinder 5, but the root cause has not been determined.

Has anyone else had this problem or know what the root cause might be?

Any and all help appreciated. Oh, btw, it is a Tiptronic.

Thanks much,
Kurt

Ahsai

Did the tech rule out the #5 plug and coil already?

X51

Yes, he did. Sorry, forgot to mention that.

Barn996

Did they read the CEL code?

Sneaky Pete

Right on Steve.....the codes are key

X51

My understanding is that the #5 misfire was the code from the CEL readout.

laz74

Double post.

laz74

Was it raining today or did he recently wash his car?

Due to the orientation of the intake, water can get in there. Cylinder sucks it in, engine misfires, CEL lights up like a Xmas tree...

If this was the case, clear the code and all will be well.

fpena944

Check and see if the cats are plugged. I was getting random CELs for a while. Replaced all of the coils and still nothing.

Discovered my cats were clogged and that fixed my problem.

X51

laz74: Weather was dry and car had not soaked at any time when it occurred.

fpena944: If it is the cats, why would the CEL readout be a misfire in a cylinder?

X51

Fernando - btw, the readouts have been the same each time, if that's helpful for any other clues as to what it might be...

Ahsai

Maybe the cylinder #5 valve tapet is stuck at the idle position even after variocam has kicked in after 3500rpm

silotwo

This is not a diagnosis just stating a possibility. I had a similar issue with my 2004 C2 a few years back. Code was for a misfire in cylinder 6 but I also had the "drive to workshop" warning. Turned out to be a lifter stuck on the high side for vario cam. In addition to the CEL it ran extremely rough.

X51

Ahsai and Silotwo - great suggestions. Silotwo - he got the "drive to workshop/dealer" warning as well. Might be onto something here. Will check it out!

Thanks much.

fpena944

With mine the cat was plugged just on one side. It would perform fine under 4k RPM but once I hit 5k RPM it would always come back as a misfire. It was very confusing because the coils were replaced, variocam was checked, and it was always one cylinder (sometimes two) that would report the error.

I never received any error codes except for the misfire.

One easy way to test this is to disconnect the cats and run the car for a bit. If it doesn't do it then you might be on to something.