Car Suddenly Became Louder, Lost Power

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?

Cracked exhaust manifold?

Cracked mufflers?

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.

daylight will bring the answer I am sure

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.

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!

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.

loose spark plug (s)

bad MAF sensor?

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.

Quotes source post: 10287086

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.

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)

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.

Quotes source post: 10287301

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

Exhaust system leak? SAI system intact? Spark plugs? WAG'ing

This thread: http://forums.rennlist.com/rennforum...-bank-1-a.html Second video of bank 1-3. I am getting this sound. This exact sound. Though it's not all the time.

Linky not worky for me?

Got the car up on the lift. Checked every square inch of the exhaust system from manifolds to tips. I'm fairly good at this, because when I got the car, it had TONS of exhaust leaks in every possible location, and I painstakingly replaced the entire system (manifolds/gaskets/bolts). Snapped off a few manifold bolts in the process, drilled them out, re-tapped etc. Got my hands bloody and dirty, but in the end it was air tight. So anyway, did a smoke test, only very tiny leaks in one area where the cat pipe meets the muffler pipe, and another extremely small leak where the 1-3 bank manifold bolts up to the cat pipe. Not enough to cause power loss or sound increase. A tiny bead of gasket sealer would probably make both leaks go away. Also determined that the car was low on oil (just changed it back in November, car is driven once a week, no oil leaks because I replaced the leaky RMS back in Nov/Dec also). While I had it up on the lift, I realized that I hadn't changed the battery since buying the car. Battery had some crusty old Japanese stickers on it, and since my car was brought over from Japan at least 6 years ago, and since the battery seemed to be weak (remote door locks wouldn't work after 4-5 days of being parked), I replaced the battery with a large Bosche unit. After the oil top up, and the new battery, the car does drive remarkably smoother, and doesn't seem to stumble or hesitate. Gear shifts actually feel smoother as well. The battery was definitely suspect. As for the mystery louder exhaust note, I'm going to guess it's a muffler that is damaged on the inside, or a loose plug, but I didn't have time today to remove the wheels/mufflers/pipes/bumper to get at the plugs. The plugs were definitely torqued to spec two months ago when they were changed though, and correct me if I'm wrong, but the 2002 tubes are different than the earlier tubes that were prone to going bad and needing replacement. A mechanic working in the bay next to me ventured a guess that my MAF sensor might be on it's way out, because he'd seen a number of cars with K&N intake units installed that eventually developed mad MAF sensors. I was under the impression that the MAF sensor was something that either worked or didn't work. Is it possible that it could be damaged or bad, without throwing a CEL?

Quotes source post: 10289040

IIRC 2002 is the 3.6L motor and no they do not have the plastic oil tubes around the spark plugs. Mad MAF? http://en.wikipedia.org/wiki/Mass_flow_sensor explains how MAF works, typical problem with K&N filters is the oil being pulled and deposited on the sensing surface to cause incorrect sensor output to the fuel control computer, how that or even a defective MAF would/could cause high exhaust volume while the engine now runs well now and not produce a CEL is beyond me.

Dump the K&N CAI.

interesting - I am following your progress

"(remote door locks wouldn't work after 4-5 days of being parked)," Normal operation. After 4-5 days the car goes "dark" to save on battery. You then have to open the door with the key and get the key in ign within 15? seconds or the alarm will go off. There is another way to keep the alarm from sounding while opening with the key. Read the manual.

Still smart to get rid of a 6+ year old battery. Did you run the car on the lift?

Quotes source post: 10291117

why? I have had batteries last a lot longer (and shorter) than that - get rid of it when it needs replacing - it's not like it will cost you $15k if it dies

Quotes source post: 10291508

True but some don't want to gamble on being stuck on the side of the road. At the very least, it can be a time issue if you have AAA. If not, the tow bill could be the same or more for a new battery as well.

Normally batteries don't just die in an instant. They give plenty of warning. Now if you reverse the polarities by accident or leave the lights on over night, that's a different story.

Quotes source post: 10291669

Exactly. Many times batteries give warning. Many times they do not. My unfortunate exprience is they do not usually. 3 of the last 4 I replaced (all different cars) that gave no warning, all chose the most inconvenient time possible to crap out. And NEVER at my own house. At my age and when they are 6 years old, I can't be bothered to deal with that ever again, so when they get that old, the first time I see a decent battery sale, for a battery I want, I get it. Unless I get an earlier warning first. A weak battery, which may start your car, also places a heavier load on your alternator, saps you of some power. And if you are not careful, can toast the regulator. For $100 every 6 years, WTF not? My yearly oil change costs more than that. Compared to tires, batteries are free....

On a related note, if you become stranded for any reason and your kids are with you, the flat bed driver might not be able to transport your kids if they are below a certain age in some states. I found this out the hard way when my water pump blew on another car.

that's just an opportunity for a nice walk with the kids - quality time

Quotes source post: 10287086

+1

I'll have to get the car back up on the lift within the next few weeks. I'd hate to think that a plug or plugs would come loose so soon after being replaced and properly torqued. It's a royal pain getting to the plugs on this car, but it's something that will need to be scratched off the list. As it is right now, with no cats and fabspeed headers/mufflers, the car is so loud that tracking down the source of the additional sound is challenging. I may, for the sake of everyone around me, and the environment, put the OEM cats back on....maybe...... The battery was definitely on it's way out, and I replaced it because I actually have no way of knowing when it was previously replaced (though it was at least 6 years old), and judging from the condition the car was in when I bought it, I figured it was better safe than sorry. The battery was basically flat when I first got the car. It would be dead after 24 hours in the garage, so I started driving the car a bit more. A few times the car needed a push/jump start, but then I got into the habit of driving it twice a week just to keep things oiled and charged. The car is a lot less 'sluggish' with the new battery, and the idle is a lot more consistent.