Strange engine noise

[GGs99]

Maybe you can help me figure something out...I have a '99 FRC...whenever the engine comes under load at low rpm (most noticeably in 4th or 5th gear) I get a strange fluttering noise coming from the left bank of the engine. It sounds very much like an exhaust leak. GM has replaced the H-pipe, left exhaust manifold and gasket.

Any ideas???

[fatherlarry]

GGs99,

Welcome aboard!

Unfortunatley, Corvette Kotze, can fix Corvettes, but he wrecked his computer this week. It's out for repair and he should have it back this week. In the meantime, I called and left him a message. I will relay the post to him and get you an answer ASAP.

If it's any help, I had a similar problem with mine and it was exhaust related, but let's wait for Corvette Kotze. He'll be on board shortly....FatherLarry

[MKOTZE]

Hello GGs99, First I need you to answer a few questions. Did any of the repairs completed have an effect on the noise in anyway? Did a technician drive with you and verify the noise? If so, What was their opinion about the noise? Does the vette have the original,factory air cleaner system or an after market system? Does it make a difference when the engine is cold compared to when it is hot?Is there any other unusual problem that you have noticed?Let me know and I'll get back to you ASAP! Thanks, Corvette Kotze

[GGs99]

Good morning. None of the repairs made so far have made a difference in the noise. The noise has been verified by two separate technicians who both thought it was exhaust related. I have installed a Donaldson Blackwing, but the noise was present with the stock box on the car. The noise appears to be worse when the engine is at operating temperature, and is most prevalent at low rpm's on a pull. The noise sound just like an exhaust manifold leak (or what I remember from the old hot rod days), but you don't hear it at idle or higher rpm levels. When the dealer could not isolate it, they called GM Tech line and they hinted at detonation. It is not a knocking or pinging noise. Someone else has hinted at an 'injection check valve' because the noise sounds like it is originating right in the middle of the left bank.

Thanks for any help...it doesn't keep me from driving the car, but it is annoying for a car like this!!!

[fatherlarry]

GGs99,

Unfortunately, Corvette Kotze's computer didn't last the night. He brought it back to Gateway again, and their putting a new hard drive in. Should have it back on Tuesday.

I did have a chance to talk to him, and he said that when he did a ring job on a 2002, that there was an electric air pump and it is computer controlled. When the car starts you can hear the pump go on, and when the car runs for about 35 - 40 seconds when it warms up, it will turn off. If that check valve is bad, it is possible that you would get that noise. He was surprised that if they removed the left bank manifold and replaced it, that they didn't notice if there were any black marks from the leaking of the exhaust hose.

Because you are coming close to warranty expiration, I would let them check that, even before you hear from Corvette Kotze. Also, if your warranty runs out, and you still have that problem, if your dealersship is customer focused , they will honor the repair as an existing problem while under warranty. Some dealers like to replace things, so they get paid under warranty, even though it doesn't solve the problem. This insures the customer keeps coming back until they get it right. Not all dealers operate that way, and I'm not saying yours does, but it is something to think about. Corvette Kotze will get back to you. Let us know how you make out with the dealership. I strongly suggest you go back with it.

FatherLarry

[GGs99]

Did Mike ever get his computer up and running???

[MKOTZE]

Hello GGs99, I am back up and running finally! How have things been working out so far? Have you gotten anymore satisfaction from the dealer? Is there anything new or different in how the car is performing? Let me know. Corvette Kotze

[GGs99]

I have not been back to a dealer. My car is technically out of warranty although I purchased an extended from Warranty Direct - the company that underwrites most dealer's extended warranties. The problem is that I have not found anyone yet that appears to have a clue where the noise is coming from. Everyone recognizes it and validates that it is not normal, but that is all the further I get.

[MKOTZE]

Hi GGs99, Sorry things haven't worked out so far. Without being able to physically look at the car I'm not able to diagnose it any further. However, I think you should try to find a dealer who will honor your extended warrantee. Then have them investigate it further. Even if the warrantee doesn't cover everything it could be worth it. Also, ever hear the saying a squeaky wheel gets the oil? You could always return to the dealer and continue to complain since this has been an ongoing problem they may honor the warrantee even if it is not covered under the extended warrantee. Good Luck! Corvette Kotze

[MKOTZE]

Originally posted by GGs99
Good morning. None of the repairs made so far have made a difference in the noise. The noise has been verified by two separate technicians who both thought it was exhaust related. I have installed a Donaldson Blackwing, but the noise was present with the stock box on the car. The noise appears to be worse when the engine is at operating temperature, and is most prevalent at low rpm's on a pull. The noise sound just like an exhaust manifold leak (or what I remember from the old hot rod days), but you don't hear it at idle or higher rpm levels. When the dealer could not isolate it, they called GM Tech line and they hinted at detonation. It is not a knocking or pinging noise. Someone else has hinted at an 'injection check valve' because the noise sounds like it is originating right in the middle of the left bank.

Thanks for any help...it doesn't keep me from driving the car, but it is annoying for a car like this!!! Hello GGs99, I just became aware of a new service bulletin from GM that may have something to do with the noise you have been hearing. It is for an Audible Spark Knock (Detonation) for models 1998-2002 LS1. This condition may be a result of corrosion of the rear bank knock sensor due to water intrusion into the sensor cavity which may occur with frequent washing of the engine. So be sure to have it checked by your dealer. Good luck :chevy: MKOTZE