What is this noise?
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Senior User
Joined: Jul 2004
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What is this noise?
recently my truck has been making a funny noise. Whenever i hit the gas i hear like a rattling noise, kind of like a nut rolling around...but as soon as i let off the gas it goes away...what could this be?
Elder User
Joined: Jan 2003
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From: North Dakota
Detonation. Also referred to as "spark knock," "pinging," "knocking," "pre-ignition," etc.
Several things can cause this: timing set too far advanced, egr valve not functioning properly, poor fuel, extremely high temperatures, vacuum leaks causing a lean condition, spark plug heat range too high, any other cause of a lean condition, or carbon build up causing "hot spots" in the combustion chamber...
A light spark knock or pinging under acceleration is normal - this lets you know that everything is at the "ragged edge" causing the best performance and fuel mileage. Heavy knocking or the sound of rocks in a coffee can is not good.
First thing I would do is check for codes stored in the computer - I had a bad egr valve that only caused the check engine light to flash once in a while, never noticed it until I pulled codes...
Several things can cause this: timing set too far advanced, egr valve not functioning properly, poor fuel, extremely high temperatures, vacuum leaks causing a lean condition, spark plug heat range too high, any other cause of a lean condition, or carbon build up causing "hot spots" in the combustion chamber...
A light spark knock or pinging under acceleration is normal - this lets you know that everything is at the "ragged edge" causing the best performance and fuel mileage. Heavy knocking or the sound of rocks in a coffee can is not good.
First thing I would do is check for codes stored in the computer - I had a bad egr valve that only caused the check engine light to flash once in a while, never noticed it until I pulled codes...
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Joined: Jul 2003
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You didn't say whether it sounded like it was coming from the engine or up through the floor. If it seems to come up through the floor, it could be your Catalitlic Converter or it's heat shield being loose. I had an '84 F-150 and the crap in the converter broke up and got loose (I guess because of age) and whenever I really put my foot in the gas it would rattle but once I let off or moved to a constant speed it would stop. Just another thing to check.
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Joined: Sep 2004
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From: Sioux Falls, SD-summer, Brookings, SD-fall
along with the catalytic converter it could be one of the baffle welds in the muffler broke and the baffle is resonating when you push on the gas. this happened with my dads 2002 chevy. if it sounds like its coming from underneath and behind you id check that as well.
Freshman User
Joined: Sep 2004
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From: Sioux Falls, SD-summer, Brookings, SD-fall
well it probably wont be easy because you would have to cut it off but what i would do is beat on it with a rubber mallet and see if there is any noise or have somebody in the truck with it running and put your ear close to it while they give it gas and see if you can isolate the noise. i think that is your best bet.
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it might be your cat, sence even tho you got a new exhaust you probly dident
get a new cat.
worth a check i think so to
get a new cat.
worth a check i think so to
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the truck is a 96 with 78,500 on the clock so maybe it is time for a change...replace it with a high flow version? also does anyone know the inlet/outlet size for the 2nd cat? and do both have to be replaced or just the 2nd one?
Last edited by Firefighter8-1; Sep 20, 2004 at 10:06 PM.
Freshman User
Joined: Sep 2004
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From: Sioux Falls, SD-summer, Brookings, SD-fall
if you are going to replace them then definately get high flow ones and yes they should both be replaced. im not sure of the inlet size but i believe the outlet size of the 2nd cat is 2 1/2"
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Isolating that noise
Hey man, my 96 F150 4x4 with 83K just started making a similar noise under the same conditions. I had my daughter drive it around the neighborhood while I sat in the back and tried to figure out exactly where it was coming from. I thought something had gone seriously wrong in the transfer case and was all set to pull it last night. When I pulled the drive shaft the first U-Joint (non greasing type) was nearly seized in one direction. I am buying replacements after work today and will let you know if that was it. There was none of the tale-tale slop in the U-Joints that I usually go by to determine if I need to replace. It might be worth a check. It is easy to pull the end from the rear diff and then slide the yoke out of the transmission. Watch for fluid that might run out of the rear seal...it helps to raise the back end and put on jack stands to keep the tail shaft higher than the pan...Hope this helps!