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Engine Knock at Idle???


 
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boxil
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Joined: 27 Mar 2007
Location: moscow, idaho

PostPosted: Tue Mar 27, 2007 5:35 am    Post subject: Engine Knock at Idle??? Reply with quote

I've just recieved an 88 XJ and the only major problem the vehicle has besides high mileage is that it has an engine knock when the vehicle is idling. It doesnt make the noise at any other rpm range. just wondering if this is a simple fix or am i gonna be needing an entire new engine. would hate to get rid of it cause it drives just great except for the knock. thanks alot for your help!
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1fox2go
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Joined: 01 Dec 2004
Location: Fishersville, Virginia

PostPosted: Tue Mar 27, 2007 4:37 pm    Post subject: Reply with quote

is it a knock or the "dieseling effect" where it sounds sort of like a diesel
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96 Cherokee 7.5 inch TnT long arm Locked F/R, D44 rear, 4.56s, 35x12.50 Muds/36x12.50 TSLs
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boxil
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Joined: 27 Mar 2007
Location: moscow, idaho

PostPosted: Tue Mar 27, 2007 5:46 pm    Post subject: Reply with quote

its a knock only.
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1fox2go
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Joined: 01 Dec 2004
Location: Fishersville, Virginia

PostPosted: Tue Mar 27, 2007 6:20 pm    Post subject: Reply with quote

It could be a number of things. Rod, lifter, valve or valves etc. You could run it till it dies but there is the chance of throwing a rod and damaging the block. I would just start looking for a replacement motor or buying parts to rebuild the one you have now
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96 Cherokee 7.5 inch TnT long arm Locked F/R, D44 rear, 4.56s, 35x12.50 Muds/36x12.50 TSLs
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Brad The Best
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Joined: 14 Jan 2007
Location: Kamloops B.C Canada

PostPosted: Tue Mar 27, 2007 7:43 pm    Post subject: Reply with quote

most likely a rod , perhaps a piston pin . i would look into a new engine or rebuilding it .

does it do it all the time or only when its cold?
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c130herc
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Joined: 11 Oct 2006
Location: North Texas

PostPosted: Wed Mar 28, 2007 3:38 am    Post subject: Reply with quote

A bad/cracked flex plate will knock at idle. But this will also make a knock noise when cranking.
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88 XJ - 35" tires, T&T LA, D44/F9 Other mods
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boxil
Member


Joined: 27 Mar 2007
Location: moscow, idaho

PostPosted: Wed Mar 28, 2007 11:32 am    Post subject: Reply with quote

Brad The Best wrote:
most likely a rod , perhaps a piston pin . i would look into a new engine or rebuilding it .

does it do it all the time or only when its cold?



it doesnt do it when its cold. when the vehicle has some time to warm up it starts knocking and its only when there is no load on the engine. i've tried to listen for it when i'm in a low gear but i can't. only when in neutral or with the clutch pushed in. so i'm thinkin it might be something transmission related. its the 5 speed manual. i'm still learning alot about it so i dont really know to much about it.
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jeepthing1127
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Joined: 16 Apr 2007

PostPosted: Mon Apr 16, 2007 6:54 pm    Post subject: Reply with quote

make room for the big bad V-8 baby Razz
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tag
Member


Joined: 16 Jul 2006
Location: leeds yorkshire england

PostPosted: Sun Apr 22, 2007 12:15 pm    Post subject: Reply with quote

Hi,
I had the same sort of noise on my 2.5 manual , i could only hear it after a run, and when i left it running to open the drive gates, i was convinced it was piston slap, as i had no lack of performance and couldn't hear it while driving. So i changed the oil and filter and added a bottle of Prolong engine treatment additive. Low and behold knocking gone! I know a lot of people think this kind of stuff is rubbish but i thought what the hell!! and what can't speak can't lie.....have ago!!!.........
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Gearhead41987
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Joined: 07 Apr 2008

PostPosted: Mon Apr 07, 2008 10:10 am    Post subject: Reply with quote

Could it be that the torque converter bolts are loose?

Mine just started doing it @ 150k...
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Toliver09
Member


Joined: 16 Oct 2007
Location: Central Illinois

PostPosted: Mon Apr 07, 2008 12:57 pm    Post subject: Reply with quote

while your checking everything, check/replace the pcv valve. From the front of the motor, the pcv valve is the hose sticking out of the valve cover closest to the firewall. It comes out with a twist, shake it. If you hear something rattling its good, if you hear nothing, replace it. If your pcv valve becomes plugged it will cause build-up of engine damaging carbons and sludge in the valves from blowby. If the build-up gets too bad it will cause a knock and eventually blow out the seals of the motor.
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