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Unread 06-27-2013, 05:59 AM   #1
xXchevyXx
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2004 WJ 
 
Join Date: Dec 2012
Location: Worcester, Massachusetts
Posts: 40
Help! Engine knock.

Ok I'm driving a 2004 jeep grand Cherokee 4.0 straight six. Ill start it up and there's this nasty clanking coming from the bottom of the block.
Runs for a bit quiets down but u can slightly here it when I let off the gas. I'm praying its a loose bolt at the bottom of a piston. Anyone had this issue??

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Unread 08-20-2013, 05:46 AM   #2
xXchevyXx
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2004 WJ 
 
Join Date: Dec 2012
Location: Worcester, Massachusetts
Posts: 40
Still spent teeing away. Starting to think its just a bad lifter. Will keep you posted
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Unread 08-20-2013, 02:46 PM   #3
GTNMUDY
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1984 CJ7 
 
Join Date: Jan 2013
Location: MADISON, WI
Posts: 162
When I got my 84 CJ with the straight 6, after about 80k I developed a knocking noise. It sounded like a rod knocking. I was scared to drive it so I had it towed to a shop to check it out.

When they got it and started it up the noise was not there and they could not find anything wrong with it.

I drove it home and didnt hear it again for some time, but it did come back for ablut 15 minutes and then gone.

After talking to several jeep owners and posting on forums. Someone told me that there was a issue with the cam slightly moving back and forth and would hit the back or timing cover of the head causing a loud knocking noise and would not do any damage to the cam, so I left it alone.

I put another 40K on the engine and didnt have any issues.

I then sold the engine and swapped a 355 SBC into the jeep. The guy that bought the 6 never came back to me with a complaint about noise.

Don't know if this is something your experiencing but just thought I would post it.
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Unread 10-01-2013, 05:50 AM   #4
xXchevyXx
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2004 WJ 
 
Join Date: Dec 2012
Location: Worcester, Massachusetts
Posts: 40
Ok I've narrowed it down to this.

My particular jeep is from out west and it turns out to be a "California emissions model" I have three catalytic converters an two of which are built into the manifold. (They hug the engine which explains where I thought the sound came from) the expansion of the coils in the converters (they're not your typical cats) was the reason the sound went away after the engine warmed up. And just recently the check engine light came on I plugged in my code reader and it came up as a "catalyst error" I brought it to a exhaust specialist and he told me its gonna cost $980 (ouch I don't wanna mess with it and risk snapping a bolt inside the block) but the cat on the manifold is indefinitely the problem. Thanks for your help guys and I hope this helps.
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Unread 10-05-2013, 06:30 AM   #5
jay-h
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1989 YJ Wrangler 
 
Join Date: Dec 2006
Location: , NJ
Posts: 4,081
It's bad enough that CA people have to drive those cobbled up vehicles. It's a real shame that they are floating about elsewhere.
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Unread 10-06-2013, 04:40 PM   #6
68v
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2005 TJ Wrangler 
 
Join Date: Oct 2013
Location: Brookville, Pa
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Wonder if that's my problem?? Mine has the two cats off the manifold also I rattles bad????? I was thinking bottom end problems???
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Unread 02-01-2014, 09:44 PM   #7
xXchevyXx
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2004 WJ 
 
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68v best way to check is let the engine cool off start it up and feel the cats before it heats up I could feel the rattle
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Unread 02-01-2014, 09:46 PM   #8
xXchevyXx
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2004 WJ 
 
Join Date: Dec 2012
Location: Worcester, Massachusetts
Posts: 40
Good news is rockauto.com has the whole cat assembly and the O2 sensors dirt cheap. $250 for the cat assembly and $20 each for the O2 sensors
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