"Knocking Rod" sound, but not from the engine? Help!
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Joined: Dec 2002
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From: Riverside CA
"Knocking Rod" sound, but not from the engine? Help!
Last night I picked up a new and disturbing sound after bottoming the '87 Z52 in a whoop de doo. It sounds like a classic 'death rattle' but I can't hear it when I lift the hood. I do hear it when I look underneath the car. I found out this morning that there is no noise when the engine is cold, it shows up again after driving for a few minutes. The sound is most apparent at idle, but goes away as RPMs increase. I run synthetic oil, it's not low, and I have great oil pressure. Is it possible that I broke something in the catalytic converter? The entire exhaust system is new, and there is no apparent damage. Is a stock Vette cat a honeycomb style, or is it made up of small pellets? Are there any baffles or something that may have come loose inside? I'm thinking cat because the heat involved might change internal clearances and cause a loose part to be held tightly enough to prevent it from rattling until the converter 'lit off', at which point it might expand enough to allow movement. Also, high exhaust flow seems to pin whatever is making the noise. Has anybody every heard of a problem like this? Help!
Drifting
Joined: Feb 2003
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From: Davis CA
Re: "Knocking Rod" sound, but not from the engine? Help! (farhorizon)
I encourage you to buy a mechanic's stethoscope. It's like the medical one except that there is a metal rod at the pickup end. Sears and others have them and they are only about $10. You will use it regularly and will be amazed at the acuity. You will have no problem isolating the sound with it. Best wishes.
Steve C.
Davis, CA
Steve C.
Davis, CA
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From: Riverside CA
Re: "Knocking Rod" sound, but not from the engine? Help! (grapeknutz)
I was told the same thing by a friend who owns an auto parts business. The evening that the sound started, I had held the brakes and blipped the throttle at a light for some folks checking out the car. I wonder if that stressed the flex plate. However, I put 40 miles on the car today and I never heard the noise. Wierd!
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From: Peoria Illinois
Re: "Knocking Rod" sound, but not from the engine? Help! (farhorizon)
I had the very same problem on my 89. As you are experiencing, my noise was most obvious at idle. Sounded like a rod knocking. I took it to a local exhaust shop, come to find out it was a cat.converter that had worn out. I replaced it--cured the problem. 1989 C4--93K Hope this helps. Good Luck.
Race Director
Joined: Feb 1999
Posts: 12,772
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From: Indianapolis IN
Re: "Knocking Rod" sound, but not from the engine? Help! (sofine89)
My rod went bad, I dropped the oil pan and found emtal in the pan,, which meant poopie! I will email you the sound file if I can find it!
DUDE, .mpeg is on its way!:banghead: :banghead:
[Modified by ld85, 8:11 PM 3/30/2003]
DUDE, .mpeg is on its way!:banghead: :banghead:
[Modified by ld85, 8:11 PM 3/30/2003]
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From: Riverside CA
Re: "Knocking Rod" sound, but not from the engine? Help! (ld85)
Thanks for the AV clip, but my sound isn't like that. There's no metal in the oil, I just went through that with my bike. In fact, it hasn't come back since Saturday. If the sound comes back, I guess the car is going up on a rack, so I can examine the catalytic converter. If that turns out to be a dead end, I guess that then I'll be pulling the tin off the torque convertor and trying to examine the flex plate. I appreciate the trouble that you went through to upload the clip, though. Thanks again!
