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Unread 10-18-2009, 01:25 PM   #1
Runner6
Registered User
1991 XJ Cherokee 
 
Join Date: Mar 2007
Location: NC
Posts: 47
4.0L Compression Test Results

The 4.0L is actually in a 1987 MJ, but I thought I'd post it here as well. Hope to get some expert advice.

Had the fuel pump and all fuel injectors professionally replaced, and just completed a compression test. Here's what we came up with:

1 - 65 psi
2 - 90 psi
3 - 90 psi
4 - 60 psi
5 - 90 psi
6 - 80 psi

Although the engine only shows 97K, it was not well-maintained by the previous owner. We changed the oil immediately upon purchase, and the oil was the blackest I've ever seen. It even felt sticky. No telling when the last oil change took place.

Any opinions on what the readings above are telling us?

Thanks.

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Unread 10-18-2009, 01:43 PM   #2
blue96jeep
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1996 XJ Cherokee 
 
Join Date: Jan 2008
Location: Queens, New York
Posts: 677
if i am not mistaken the spec is 120-150 since your specs are below the minimum spec i say you need to rebuild, piston rings are shot, did you do a wet test.

-ryan
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Unread 10-18-2009, 02:36 PM   #3
Rollin
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2005 WK 
 
Join Date: Feb 2007
Location: NH
Posts: 1,242
Quote:
Originally Posted by Runner6 View Post
The 4.0L is actually in a 1987 MJ, but I thought I'd post it here as well. Hope to get some expert advice.

Had the fuel pump and all fuel injectors professionally replaced, and just completed a compression test. Here's what we came up with:

1 - 65 psi
2 - 90 psi
3 - 90 psi
4 - 60 psi
5 - 90 psi
6 - 80 psi

Although the engine only shows 97K, it was not well-maintained by the previous owner. We changed the oil immediately upon purchase, and the oil was the blackest I've ever seen. It even felt sticky. No telling when the last oil change took place.

Any opinions on what the readings above are telling us?

Thanks.
Supposed to be 150 on a 4.0l. Time for a rebuild with 4.2 rods and a 4.2 crank
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Unread 01-09-2010, 10:46 PM   #4
KevinM90
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1998 XJ Cherokee 
 
Join Date: Jul 2008
Location: Maine
Posts: 262
rings and head gasket?
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1996 Jeep Cherokee Sport. 3" lift/31" combo. Some lights. Flowmaster. 5 different horns. Full size spare. No rust. Daily driven. Will be...forever.

Last edited by KevinM90; 01-10-2010 at 12:02 AM..
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Unread 01-09-2010, 10:49 PM   #5
KevinM90
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1998 XJ Cherokee 
 
Join Date: Jul 2008
Location: Maine
Posts: 262
double post sorry
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1996 Jeep Cherokee Sport. 3" lift/31" combo. Some lights. Flowmaster. 5 different horns. Full size spare. No rust. Daily driven. Will be...forever.
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