Piston Slap or Carbon Knock?
Thread Starter
Le Mans Master
Joined: Jan 2001
Posts: 6,449
Likes: 371
From: Maryville TN
St. Jude Donor '06-13,'16-'17, '19
Piston Slap or Carbon Knock?
On my 40,000 mile 99, on cold start up I hear a knocking sound that lasts for about a mile. This just started happening a few weeks ago.
I can run through the gears near redline and the car won't knock on cold start for several days. When the knock starts again I can run the engine again near redline to clear the knock again for a few days.
Tom
I can run through the gears near redline and the car won't knock on cold start for several days. When the knock starts again I can run the engine again near redline to clear the knock again for a few days.
Tom
Burning Brakes
Joined: Oct 2003
Posts: 1,162
Likes: 0
From: Dubai
Re: Piston Slap or Carbon Knock? (TCW)
Since it is a '99 ( like mine :) ) you might want to check if any of the piston rings might have come loose ( a common problem with older wets :sad: mine had it ). :seeya
Team Owner
Joined: Jul 2001
Posts: 21,396
Likes: 1,011
From: Various places in Southern California.
Re: Piston Slap or Carbon Knock? (TCW)
Sounds like piston slap to me. Knocking from carbon deposits typically happens when the engine is hot, especially under high load/low RPM conditions.
Melting Slicks
Joined: Mar 2002
Posts: 2,931
Likes: 2
From: Tx
Re: Piston Slap or Carbon Knock? (TCW)
What you are describing sounds like carbon induced piston slap. Using the word knock gets people confused and they start to think of pre-ignition (which the carbon will also cause)
Do the decarb procedure (the one where you put the cleaner in the spark plug holes). This should help eliminate some of the carbon on your piston tops.
Do the decarb procedure (the one where you put the cleaner in the spark plug holes). This should help eliminate some of the carbon on your piston tops.
