Engine rattle under load - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 12-02-2007, 05:38 PM   #1
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Default Engine rattle under load

http://www.bonnevilleclub.com/forum/...ic.php?t=61233

Hello all,
After searching the forums with no real answers, I decided to add another thread in the strange noise category. My 96 LSS has the same symptoms as in the above thread. Many others including the above have had the same problems, but nobody has replied with a solid fix. I just replaced the HB with hopes of a fix, but there was no change in the noise it makes. I have heard that the catylatic converter can make the noise, but I havn't figured out how to recreate it. One note to add- my car does not rattle in reverse. It almost sounds like the drivetrain is reacting to torque in drive thus causing one of the rotating masses to contact the chassis. Maybe this is why it wont do it in reverse?
Can someone help me out here?
Thanks
JJ
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Old 12-02-2007, 07:13 PM   #2
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Crawl under the car and smack the catalaytic converter converter a couple of times. If it is broken up then you wil hear the pieces rattle around in it.
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Old 12-02-2007, 07:17 PM   #3
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Don't go just side-to-side when you do that. I had one fail that fooled me for a long time because it would only rattle when moved vertically.

Rule that out first, and we'll go from there.
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Old 12-03-2007, 10:25 PM   #4
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Default converter rattle

Hello again,
I checked the converter tonight and it DOES rattle. First I tried moving the entire exhaust system and couldn't get anything. But when I wack on it either side to side or up and down, it rattles. Sounds like a part of the heat shield is loose or the core is starting to break up. So you guys think that'* the problem?
One thing I noticed tonight, it looks like a 2nd converter is installed downstream from the 1st. I suppose it could be a resonator, but it has a heat shield similar to the cat. Just curious.
Thanks again everyone for the help!
JJ
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Old 12-03-2007, 11:50 PM   #5
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Downstream is the resonator. Ignore it for now.

Whether the busted up cat (core broken loose) is the rattle you hear or not, it'* a problem. Replace it and let us know if it cures the problem.

Both of the cars in my sig had cats fail. Both of them made me think I had a problem with the engine or the trans. Yes, the second one fooled me even after learning with the first, because it wouldn't rattle side to side, but a couple weeks later, I backed it up on ramps and shook it up and down.



There'* at least 3 different 'sound and rattle' modes the cat can get you with. You can get a replacement hi-flow cat from www.justmagnaflow.com (measure your existing in and out) and have a shop pop it in there for another 20 or so.
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Old 12-04-2007, 12:41 AM   #6
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Default Off to get a cat.

Will do. Thanks for the help. Without you I would have pulled the timing cover to check the chain. I will let you know what happens!
JJ
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