4.7 HO piston slap - JeepForum.com
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Unread 08-15-2009, 11:12 PM   #1
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2004 WJ 
Join Date: May 2009
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4.7 HO piston slap

Just got a question for all you experts out there.. I picked this jeep up a couple of months ago and never really noticed that when engine is cold and I start it up, after about 10-15 I get this clacking noise in the engine and it last for maybe about 30-40 secs and then stops.. It doesn't do it when the engine is warm only when its been sitting overnight.. I've changed the oil and put a good filter on there.. Could this be piston slap? It's not a heavy thud sound like if it was a rod bearing, it's more a lighter clack sound and is very speratic.. It does it at every start up but it's not a constant noise, it comes and goes in that 30-40 secs..

It's a 4.7 HO with 60k


JForest2 is offline   Reply With Quote Quick reply to this message
Unread 08-16-2009, 07:28 AM   #2
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is it knocking? What fuel are you using?
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Unread 08-16-2009, 10:43 AM   #3
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My 01 standard 4.7 has done that for years. I strongly believe that it is piston slap. It's annoying, but not much to worry about.
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Unread 08-17-2009, 11:28 AM   #4
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how about a leaking exhaust manifold gasket? as soon as it warms up the metal expands and seals up the leak. I had this fixed on mine when i frist bought it.
2004 WJ Freedom Edition w/4.7 H.O. heavily modded (sunk + totaled R.I.P. 9/06)
1998 TJ Sahara lifted, locked, and tons of crap bolted on (Sold)
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Unread 08-17-2009, 11:54 AM   #5
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^ my exhaust leaks too. goes away when warm.

4.7 HO too. wonder if this is a common problem
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Unread 08-17-2009, 12:29 PM   #6
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If it does this only when cold and overnight, have you thought that you might be losing oil pressure?

Is your gauge a dummy gauge or a real gauge? Does it start off at 3/4 when cold, then settle down a little bit past 1/2 when warm? Or does it stay at the same location the entire time, regardless of engine warmth?
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2000 WJ, 4.5l, AX15, 242 D60/14b, 5.5" lift front, 7.5" rear. Ford Expedition rear coils, Ram 350 shocks, JKS, IRO Long Arms, cool Badlands flag thingy.
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