DSchaefe

My 99 FRC has spent most of the last three weeks at a dealer here in the phoenix area. After replacing the knock sensors, an O2 sensor, the rear differential seal and the catalyst, the car is making a loud loose metal sound resonating through the exhaust when the engine rpm is coming down. Makes no difference if the car is moving or not. They have replaced the catalyst twice to no avail... they now say the noise is coming from the engine... and being amplified by the exhaust...??? The car seems to run fine otherwise...

The techs at the dealership have run out of things to try... I am worried that they $%#*ed up my car... they are supposed to be getting some tech help from GM but that doesn't make me feel any better...

Any ideas? What can I do?

Dave

ArKay99

It sounds like you are describing pinging or knock! But how can that be on decel? I wonder if when they reinstalled the manifold over the knock sensors they pinched a sensor lead. Is this the reason the car went in?

DSchaefe

It isn't a knock or ping noise. It sounds like there is loose metal in the exhaust... very tinny noise and only on deceleration in rpm... When you rev, all is fine, no knock or ping... when you let off, loose metal! They have tested the exhaust all different ways and have used three different catalysts to no avail...

Thanks for the ideas... I don't know much about the knock sensors or how they are replaced.

Dave

Heikar1

I have a 99 coupe MN6. I experienced the same noise after I installed a Corsa exhaust several years ago. There is a thin metal heat shield on top of the mufflers (can't recall if they were actually attached to the mufflers or the chassis) that can make contact wtih the mufflers and causes a tinny, rattly metallic noise. I readjusted my exhaust slightly and tried to bend the heat shield moderately with hand pressure only, to prevent contact between & the muffler. So far so good.

When I had my headers installed, I had a similar issue and found that the exhaust pipe (exhaust hoop area over the axle) was making occasional contact with the body just inboard of the right wheel well. Again adjusting the exhaust solved the problem.

Good luck...those little annoying noises will drive you nuts !

DSchaefe

Any more ideas???

69

I would look at the drive line now. Could be the Torque tube/drive shaft bearings........or how is the clutch?

Longhorn FRC

Mine does the same thing... I'll check out the heat shield thing tomorrow and pay close attention to this thread...

1hkdup996spd

I know exactly what you are talking about. My 99 makes the same noise. I asked several places and they couln't tell me what it was. I'm going to check the heat shield on my indys but it I don't think that's it. It sounds like it's coming from the engine. I hope someone can help us out. :confused:

bowtiebandit

How loud is it on a scale to from 1 to 10..1 being a whistle and 10 being a rod knock?

ROJO99

:lurk: .

DickieC.99

I have the same problem on my 99. I've been hearing it almost since the car was brand new, even before the borla. I have absolutely no idea what it is. I think it sounds like it coming from underneath the car - specifically in front of the right rear wheel where the exhaust pipes meet :confused: ...1-10, I would probably give it a 3. Its enough that I've had friends ask me, "what the @%$#! is that?" :banghead:

1hkdup996spd

I'd also say it's a 3 on a 1-10 scale :iagree:

DSchaefe

I have been out of town... while I was away the dealer had my car and was trying everything they could think of... all to no avail. I would put his noise at a 5 or 6 on your scale. The last thing you want to hear when you rev your Vette is loose metallic noise making it seem that your car is falling apart... PLUS it is very bad for resale!

The dealer now tells me that it is in Chevrolet's engineer's hand. They say they know of six cars in the Phoenix area with this problem and currently have no solution. I still cannot understand how the this noise suddenly appeared when recent work was done (new catalyst - twice, knock sensors, o2 sensor and differential seal). Any common denominators here for folks who also have this noise?

I am going to call Chevrolet corporate and lodge my complaint today. In my opinion this is caused by the dealer as outlined above... and exacerbated by Chevy's inability to understand their own designs! My BIGGEST gripe is that this KILLS any resale value this car HAD!

My Acuras NEVER had problems like this.

Dave


[Modified by DSchaefe, 3:59 PM 12/8/2003]

Valdostavetteguy

I had the EXACT same problem with my '99 MN6 Coupe. After trips to three different dealers I found the problem myself. One of the oxygen sensors located near the CATS was loose was loose...so loose I could turn the bolt with my fingers.

I tightened it up (added some lock-tight) and haven't had the problem since!

Hope this helps! That damn noise likened to drive me kRaZy! Oh, and my friends were saying the same thing...embarassing huh!

Juan :)

DIAMOND DAVE

If not the loose sensors, you may want to check the mufflers for loose internal parts...whack them with a mallet and see if you hear anything.

bowtiebandit

DSchaefe...do you know if they pulled the diff from the car to reseal or did they do it while it was in the car?

Clutch engaged or not?

I have seen several things cause a similiar concern

1. Pebbles stuck inside the fuel tank heat shield
2. Mufflers being put in the mounts in the wrong slot, rubs the bumper support
3. Mufflers rubbing the heat shield just above the differential
4. Brake lines buzzing on the rear cradle, especially if the removed it for the reseal. The retainers are usually a 1 shot deal.
5. The usuall springs just in front of the trans that support the exhaust.
6 The 02's I see quite frequently, either not tight or the collar at the top of it vibrates.


[Modified by bowtiebandit, 10:14 PM 12/8/2003]

DSchaefe

I don't know how the repair was done. The noise happens whether or not the clutch is in... makes no difference. I am picking the car up tomorrow because they say they are finished... I have also contacted Chevrolet and am supposed to have a conference call with the service manager and the Chev representative tomorrow...??? I am going to give a copy of this thread to the service manager and see what he says... I will definitely post an update... Thanks for all the feedback...

Dave


[Modified by DSchaefe, 9:23 PM 12/8/2003]

DSchaefe

Well I am now at the end of my reservoir of patience. I gave the dealer a copy of this thread... they said they have either tried all of the fixes mentioned or that the problems mentioned aren't necessarily the same as the one my 99 FRC is experiencing. I have the car back and the noise is as bad as ever. The dealer has no other remedies to try. they have mounted two different new catalysts and one used one, with no success. They have called in a GM engineer who acknowledged knowing about at least six other cars in the Phoenix area with the same problem. He said that the technical staff at GM are "working on it".

I called the Customer Assistance line at GM and got absolutely no help. I am glad it was a toll-free number because I would've hated to pay for that worthless call. The guy on the other end of the phone stated basically the same thing the dealer did, that the technical staff on the dealer side at Chevy are "working on it". He also stated that neither he nor I can contact the technical staff because they are on the dealer side... so he/I cannot get an estimate of how long they will be "working on it" or when they will fix it. So I told him I will be calling every two weeks for an update on the status and that if he cannot get an update that I am going to keep calling his boss and his bosses boss until I get some answers. I am also going to write a nice letter to Bob Lutz and some other GM bigwigs... and conveniently copy all of the auto magazines and some other folks who may be interested. I'll also post it here for all to see...

The bottom line is this: Who knows how long they will be "working on it" before they find a solution. It could be days, weeks, months or years. I can only guess that since so many others are experiencing this problem that they haven't devoted any resources to fixing it. they are more concerned with the damn C6 which I will definitely NOT be in line for. This problem did not exist until the above referenced repairs were completed. Until this noise is repaired the car is unsaleable. I know that a good mechanic could completely tear-down the engine and drivetrain and rebuild it in less than a month... why can't they get a solution to this in a reasonable amount of time? Why can't they just say that they will get back to me within X weeks and they will either have a solution or they will replace the entire exhaust system...??? I have been sadly reminded that I hate General Motors and have absolutely no confidence in their manufacturing, design, engineering or, most irritatingly, thier customer service.

I can only imagine how the real car companies (insert your brand here) would handle this...

Dave

:mad :mad

DickieC.99

That really sucks. When will they realize customers come first?

I was wondering if any of you that have FULL aftermarket exhaust have this problem - OR - if you had this problem with anything stock, but no longer. I'm just trying to eliminate anything possibilities.

DSchaefe

ttt - every vette owner should read this...