Does this sound like a bad cat?
Thread Starter
Melting Slicks
Joined: Aug 2000
Posts: 2,009
Likes: 1
From: Springfield MO
Does this sound like a bad cat?
I have a knocking noise coming from the exhaust. I jacked it up and according to a stethoscope the noise is coming from inside of the drivers side cat. Could it have come loose, banging around in the exhaust. Its not the motor because I just got it back together today. The noise is inconsistant with the rpms. It doesn't knock anymore at 2000 rpms than 4500 rpms. A week ago I thought it was a broken valve seat or even busted wrist pin. So I took it all apart agian only to find a perfect cylinder wall and a perfect head with no valve problems. After all this the noise is still there, I am going to open the cat tomorrow, I was just wondering if anyone else has had this problem. Thanks
Le Mans Master
Joined: Mar 1999
Posts: 9,663
Likes: 1,682
From: Fort Worth Texas
2024 Corvette of the Year Finalist - Unmodified
2023 C8 of the Year Winner - Unmodified
2020 Corvette of the Year Finalist (stock)
2019 C7 of Year Winner (stock)
Former Moderator
Cruise-In I-II-III Veteran
Re: Does this sound like a bad cat? (AS84)
might be.... I noticed on Diacom that my knock sensor was always going off..... The motor and chip are stock and I run 93 octane in it with a 160 stat in the summer. It shouldn't be knocking at all. When I replaced the bad cats last Tuesday, the passenger side cat was broken up inside. I noticed today when I took the car out with Diacom on there, that there was no more knocking like it used to do. Maybe the rattling cat is setting the sensor off? Don't know but maybe it's possible.
btw, I got a code 32 today cruising on the highway since I have no pre-cats anymore. Went home, re-programmed the chip disabling the code 32 diagnostic check, and drove out the same highway and no more code!
btw, I got a code 32 today cruising on the highway since I have no pre-cats anymore. Went home, re-programmed the chip disabling the code 32 diagnostic check, and drove out the same highway and no more code!
Le Mans Master
Joined: Mar 1999
Posts: 9,663
Likes: 1,682
From: Fort Worth Texas
2024 Corvette of the Year Finalist - Unmodified
2023 C8 of the Year Winner - Unmodified
2020 Corvette of the Year Finalist (stock)
2019 C7 of Year Winner (stock)
Former Moderator
Cruise-In I-II-III Veteran
Re: Does this sound like a bad cat? (AS84)
it probably will, but I can remove the flag in the chip for the code if you want.
Le Mans Master
Joined: Jul 2001
Posts: 6,252
Likes: 2
From: Silicon Valley Kalifornia
Re: Does this sound like a bad cat? (AS84)
I had a problem like this and it turned out to be the INSIDE pipe of the front Y pipe was cracked. There is an outside pipe AND an inside pipe. If the inside one cracks, and my did right near the header, it will knock and rattle. You'll never see it. From underneith the car, hit the the Y pipe with a rubber malet. You should be able to hear it. Good luck.
[Modified by GRX, 6:12 PM 12/1/2001]
[Modified by GRX, 6:12 PM 12/1/2001]
Le Mans Master
Joined: Dec 1999
Posts: 8,540
Likes: 1
From: And on the fifth day, subpoenas were served to Obama senior staff
Re: Does this sound like a bad cat? (Marcho Polo)
Craig -
When you had the intake off, did you clean out the EGR passages? Working on a theory on the 32 with low restriction exhaust.
I have no pre-cats and a low restriction main and a 3" B&B and no code 32. Think there is something else going on!
I would be interested to know how / if the fuel trims and timing tables deal with EGR on/off. Does the ecm depend upon the O2 to catch the change in mixture, or is there a different table for this. Does the timing table change for those conditions where EGR would be active?
________________________________________ _______________________________
On the cats - My precats were making a racket under "lugging" conditions. I'm sure it caused some retard. Now nice a quiet. BTW, when the pup cats went they took out the main by blowing mahunckers into it as it grenaded.
When you had the intake off, did you clean out the EGR passages? Working on a theory on the 32 with low restriction exhaust.
I have no pre-cats and a low restriction main and a 3" B&B and no code 32. Think there is something else going on!
I would be interested to know how / if the fuel trims and timing tables deal with EGR on/off. Does the ecm depend upon the O2 to catch the change in mixture, or is there a different table for this. Does the timing table change for those conditions where EGR would be active?
________________________________________ _______________________________
On the cats - My precats were making a racket under "lugging" conditions. I'm sure it caused some retard. Now nice a quiet. BTW, when the pup cats went they took out the main by blowing mahunckers into it as it grenaded.
Burning Brakes
Joined: Feb 2000
Posts: 1,206
Likes: 0
From: USA USA
Cruise-In II Veteran
Re: Does this sound like a bad cat? (AS84)
I just took off my cat few days ago. It was loose and rattling around inside
there. I'm stuck my fingers in one end and moved it and the
opposite end did not move!! Probably at least two or three pcs. Sticking
A TEST pipe on it t-morrow! Can't wait to hear the sound w/no cat and
eliminators!!!!!!!! :cool: :yesnod:
Matt
there. I'm stuck my fingers in one end and moved it and the
opposite end did not move!! Probably at least two or three pcs. Sticking
A TEST pipe on it t-morrow! Can't wait to hear the sound w/no cat and
eliminators!!!!!!!! :cool: :yesnod:
Matt
Corvette Stories
The Best of Corvette for Corvette Enthusiasts
Top 10 Most Expensive Corvettes Ever Sold on Bring A Trailer
Brett Foote
10 Things Every Corvette Owner Needs (2026 Edition)
Michael S. Palmer
8 Most "Only Corvette Owners Understand" Quirks and Problems
Pouria Savadkouei
10 Reasons the C6 Z06 is Still A Performance Benchmark After 20 Years
Joe Kucinski
How Much Horsepower Every Corvette Engine "LOST" in 1972
Joe Kucinski
Top 10 DOs and DON'Ts for Protecting Your Convertible Top!
Michael S. Palmer
Top 10 Most Explosive Corvettes Ever Made: Power-to-Weight Ratio Ranked!
Joe Kucinski
150 hp to 1,250 hp: Every Corvette Generation Compared by the Specs That Matter
Joe Kucinski
