Knocking coming from Cats
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Knocking coming from Cats
I have a knocking that started at about 70K and has gotten louder since. I am at 130K now. With my scope I have found that it is loudest coming from the Cats. The rest of the exhaust and engine is fairly quiet. It gives the impression of a "Rod Rap" but no noise coming from the oil pan. When the truck is put in drive and is under a load the noise dissapears. Any ideas?
Thanks, Ray
Thanks, Ray
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Joined: May 2004
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From: Abilene Kansas
the stuff inside has broken loose and its rattling. my ideas are to take the cats off, empty them and put them back on. but this isnt exactly legal. you could replace them with an aftermarket cat
Matt
Matt
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Thanks, But
Hi Matt, Thanks for your quick response. The sound is a "Knock" not a "Rattle" could it be the engine noise echoing in there? Have you run across this before? Thanks again, Ray
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The Cats have a mesh coated with metals.
If they break up, why would you not think a knocking sound cannot result when hot exhaust gas is pulsing against the pieces?
If they melt or stack up, they can block the path.
I would look at the rear Ox sensor output for stability because it monitors the front CAT efficiency. The voltage should stay relatively in a narrow range and NOT follow the front a significant amount. A comparison need to be done to see this.
When the front cat begins to fail it's function, the rear Ox sensor will cause a code to be set at some 'later time' when the system 'fails out of limit tests' the PCM does. This is why there are rear Ox sensors.
If they break up, why would you not think a knocking sound cannot result when hot exhaust gas is pulsing against the pieces?
If they melt or stack up, they can block the path.
I would look at the rear Ox sensor output for stability because it monitors the front CAT efficiency. The voltage should stay relatively in a narrow range and NOT follow the front a significant amount. A comparison need to be done to see this.
When the front cat begins to fail it's function, the rear Ox sensor will cause a code to be set at some 'later time' when the system 'fails out of limit tests' the PCM does. This is why there are rear Ox sensors.
Hotshot
Joined: Mar 2011
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I had a weird noise coming from the cat/muffler area of my '97 with a 5.4.
It turned out to be a breakdown of the flange where the pipe connected to the muffler. It seemed like a lot of trouble to disassemble the exhaust system and replace parts when it otherwise worked, so I got a small roll of stainless steel wire from Harbor freight and wrapped the flange with it. 5 years later the noise is still gone.
It might we worth a look....
It turned out to be a breakdown of the flange where the pipe connected to the muffler. It seemed like a lot of trouble to disassemble the exhaust system and replace parts when it otherwise worked, so I got a small roll of stainless steel wire from Harbor freight and wrapped the flange with it. 5 years later the noise is still gone.
It might we worth a look....
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