Oh crap. What should I do?
 

Today I was at Road America for a track day. MVP Track Time does a great job, and puts on a great event. It's well run and the instructors (at least the one I was with) are very good.

However, on my third session, coming out of turn 13, I noticed a vibration. I immediately backed out of the throttle partially just to get around the last corner to the pits. I didn't hear any weird noises. When I got into pit lane, I up shifted so I was running at lower RPM, and the vibration went away. So I drove back to the paddock keeping the revs fairly low. I let the car cool. After a while I took the car for a drive outside the venue. Across the street was a country road, and I headed down it. I played with speeds and there was no vibration up to 50mph. Then I turned around and played with RPM. Above about 4000 rpm, the engine felt rough, and gets worse at higher RPM (only went to about 5k). Because it felt very consistent and even, it feels like a vibration. Again, as long as I kept the RPM low, the engine felt fine.

So I packed my stuff up, crossed my fingers and started my 2.5 hours home. Luckily, the drive is almost all highway, so I just kept the revs below about 3500 and drove it. I got home with no problems, and by that time I was thinking that maybe I had imagined the problem, or that it was something other than the engine. I needed gas, so I stopped close to home, and on the way home from the gas station, I drove it up into the 4000 rpm range in 1st gear (slow speed). Yup. Same problem.

When I was driving the track, I noticed a vibration in the car a couple of times before this. In a hard turn that I got into a bit hot, I would get a bit of under steer and felt a vibration that I'm pretty sure was from the front tires. When I had the problem, I initially thought it was the same thing, but it didn't go away when I got going straight again. I've been racking my brains over this, and I'm pretty sure it was a different feeling vibration, but I could be wrong.

No fluid leaks, no funny noises. It really just kind of feels like at higher RPM the engine starts running on 5 cylinders or something. It feels like it's running rough, but it's a completely regular, consistent roughness. It's not something where it runs lumpy or anything. It's not like the mixture is out of whack and the car is just running crappy.

So now I don't know what to do. I'm thinking about changing the oil and maybe getting an analysis (unless I obviously find metal particles, then I know it's an internal failure). I don't know if I should take it to my Porsche shop (Fischer Motors) or what. What do you guys think I should do to ID the problem?

Could be a spark plug or coil, it could also be that you lost a wheel weight. Does the vibration come with a loss of power?

I'm pretty sure that your check engine light would illuminate if you lost a coil pack or a spark plug. I had a CEL illuminate when one of my coils went bad.

I don't think it is a wheel weight. The vibration from a wheel weight would be dependent on the car speed, not the engine speed.

Its not internal. If it was you would have scattered the engine on the 2.5 hr trip home..

Probably a coil pack died or came unplugged and no the CEL won't illuminate in some of these instances. You also could have fouled a spark plug..

Wheel weights come into play when high wheel speeds are high, so if the issue happens in first gear above 4K RPM you can bet its not a wheel weight.

IMO, a wheel weight can play havoc at any speed depending on a myriad of factors including how heavy said weight is. The key is a lost wheel weight may be dependent on a particular speed to experience but will not be intermittent in nature in respect to repeatability.

Thanks for the input guys. It is definitely not speed related, but it is definitely rpm related. A coil pack makes sense. The engine does really feel like one cylinder isn't firing at all above 4k rpm. I think a plug wire would be intermittent. I'm going to pull the plugs today and see if any have a different look to them or smell of unburnt fuel. I may do a spark test on them too.

Thanks again for the input. I'm glad Jake thinks it's not internal. <whew>

C'mon, Mike...is it speed related or not?? :D

:p

Fixed.

So... what was the fix? :confused:

Read his 9:23 post (which used to say, in part: "It is definitely not speed related, but it is definitely speed related.") and my 9:45 post. That was the "fix". (Far as I know, the car still needs work.)

have you ruled out the engine mount?

Well, I kinda did automatically because it didn't seem related to torque. If it were an engine mount, I'd think that torque would cause the engine to rotate (equal and opposite to crank rotation) regardless of rpm. The rotation of the engine would cause some kind of vibration-type feeling.

Does anybody have any suggestion on how I can troubleshoot the problem and identify what's causing it?

do you have a durametric unit??

Nope. Wish I did though.

Here's what I did recently... I bought the Durametric, and showed Cyl misfire #5. So... I swapped coil pack between cyl 5 and 6 and guess what??? The next CEL code threw a Cyl misfire in number 6. Bingo!!!

So...

1. read your code on the Durametric
2. swap coil packs on adjacent cyl AND...
3. swap plugs on OTHER adjacent cyl
4. clear the Durametric code
5. drive car, run engine up to the 4k+ RPM
6. let engine cool, drink a beer (or two)
7. read the code again and see which cyl the problem follows
8. order parts
9. take girlfriend out to dinner

This procedure took me an hour or so. I'm assuming you have ignition issue, and guessing a fouled plug. My coil pack issue wasn't rpm related, it was intermittent. I hope this helps.

:cheers:

I owned my NB for about two years before I bought Vag-com. Durametric will be one of the first tools that I buy most likely before I buy my 986. Most certainly if it tells me that rev history on the engine.

"Does anybody have any suggestion on how I can troubleshoot the problem and identify what's causing it?"


Jack up your car, pull the spark plugs and inspect the plugs and coil paks. The misfire cyl spark plug tip will be discolored (usually black or wet) compared with the other 5. Inspect the coil pak on the offending cyl and look for cracks or signs of arcing. Replace failed parts. Easy breezy.

The Durametric is nice but any simple $60 OBDII reader will also give you misfire codes that identify which cyl. is the problem.

One simple thing I forgot to mention... stop by Autozone and get them to read your code with their Actron. Not as detailed as a Durametric, and dont think it can clear codes, BUT you might get an early indication while you're waiting on your $300 Durametric to arrive in the mailbox :)

I don't have a CEL so AFAIK, I won't have a code.

I do have an AutoTap, which is supposed to work on all poast-'98 cars. So that should give me diag info. I'll try it this weekend.