offshoreMM

I have a 2002 C2. I was driving around 30-40mph on a road that was in poor condition, obviously not under WOT. Suddenly my car started stumbling and felt like it was losing power, and the exhaust note got louder.

I pulled over, got out a flashlight, and checked under the car for any leaks. No leaks, no check engine light. (I've already done most major maintenance on this car, RMS, IMS, clutch, belt, waterpump, etc etc etc etc. After about 20 minutes, I started the car again, and it drove ok, only now it is louder than before, and it feels like it has lost about 10-15% of it's power. As someone who has driven and worked on cars for a long time, my first guess was an exhaust leak, maybe due to the horrible condition of the road, an exhaust bolt broke, or something. It feels like the car has less back pressure now. It idles like it has a slight vacuum leak or exhaust leak.

My car has cat-delete pipes and a full stainless exhaust. I've been driving it like that for over a year, and I am acutely attuned to the normal driving sounds of the car. When variocam switches over, I can now hear the transition very loudly. It has all the hallmarks of an exhaust leak. Only problem is, when I got under the car and checked all of the flanges and bolts, they are all 100% intact, as are the 02 sensors. I cannot see a leak anywhere. I used to be able to gently drive the car in low RPMS, and it wouldn't be intolerably loud. Now it is very loud at all RPMS.

This is driving me crazy. What could it possibly be?

aviography

Cracked exhaust manifold?

Ahsai

Cracked mufflers?

Imo000

Look inside the engine compartment too, maybe the intake pipe slipped off the throtthe body. To look for an exhaust leak, lift the back end up safely, fire it up and with your hands look for the leak. Start with a cold engine, it will give you more time before the pipes get too hot.

Shark Attack

daylight will bring the answer I am sure

offshoreMM

Thanks for the feedback guys.

I've checked the engine bay because I also thought that perhaps part of the air intake assembly had come loose or disconnected. Everything is in place and not loose.

I tried to slide under the car with a high powered lamp, and from what I can see (granted it's not much), all bolts and gaskets are in place, and the cat bypass pipes are mirror smooth and not cracked or leaking.

My car has fabspeed manifolds, cat-bypass pipes from Germany, and Fabspeed mufflers, all on the car for less than a year. Finding a crack or hole in one of these pieces is going to be disappointing. I'm convinced that it has to be an exhaust leak. Both O2 sensors are in place, and snug. The exhaust fume odor is stronger than usual, and the car is exhibiting all of the symptoms. Something related to the exhaust is cracked, somewhere before the mufflers. I am going to put it up on the lift tomorrow and play Sherlock Holmes.

DBJoe996

Maybe just a exhaust header gasket? See if there is any evidence of blow-by carbon around the exhaust headers before getting into the whole exhaust system. Maybe the poor road conditions shook something loose. Good luck!

aviography

Grasping for straws here, but do both mufflers have same sound level? (assume both sides are not crossed over to each other)

If not then perhaps one muffler has blown internal baffles?

Another thought is if you can rig up compressed air to pressureize each exhaust bank by forcing compressed air into the exhaust tip and then determine where air is coming back out, at least you can do this without the engine running and will give you plenty of time as the engine/exhaust won't get hot while you determine where the leak might be. It's sort of a reverse leak-down test if you will.

ivangene

loose spark plug (s)

mcipseric

bad MAF sensor?

offshoreMM

More good input.

-I was also thinking it might be a loose plug. Having driven an old BMW that had a spark plug wire come loose, I've experienced that before too. Though when that happened, the car was basically un-driveable and stumbled over to the side of the road. I changed the plugs back in December, and everything was tight at that time, but I'll certainly add it to my list of things to check if I don't find an exhaust leak.

-Bad MAF sensor was a thought, but why the noisy exhaust leak sound? Also, wouldn't it cause a CEL? I wonder if there is a way to diagnose this, with no CEL. The car DOES have a K&N intake, which I regret buying, and will be removing in order to put an OEM system back in place.

-I also thought about the muffler being damaged. The cat bypass pipes get almost white hot, and the exhaust output isn't passing through any cats before hitting the mufflers. I wonder if the exhaust got too hot and somehow cooked/damaged the inside of the muffler. Will check to see if one is louder than the other tomorrow.

I feel that the car is running rich. I have no evidence, other than having driven and worked on countless cars over the years. It feels a little sluggish. Will cross some possibilities off this list tomorrow.

Sneaky Pete

I think Ed is onto something....how about a loose coil pack? That happened to me as well on a '73 2002 bmw and it was a loose spark plug wire. Car sounded louder and was running poor.

ivangene

a loose plug will still fire - and sound loud, and the car will still drive - with 8.33% less power

your "butt dyno" 10-15% may need re-calibration

(unless it's 2 plugs)

Imo000

Unlikely a loos plug as aluminium heads can't take the stress of a loose plug. The threads gets beaten and the plug blown out of the head in a very short time.

There is plenty of sggestions here, time to get dirty and start checking things.

ivangene

really?
https://rennlist.com/forums/996-foru...ith-video.html
post #14

https://rennlist.com/forums/996-foru...-bank-1-a.html
post #12

I am not saying this is the problem, I am saying it's a likely suspect part - and an easy fix - and a common problem

we are just diagnosing over the interwebs without seeing or hearing the car - with little to no info to go on - so it IS a valid check point

just sayin'

also dont forget spark plug tubes crack and cause air leaks