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ever seen a compression test this bad?

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Old Aug 20, 2013 | 03:35 PM
  #1  
884x4's Avatar
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From: Justin, TEXAS
Year: 1988
Model: Cherokee
Engine: 4.0
Default ever seen a compression test this bad?

my 88 4.0 is dying
264k

dry
1-167
2-125
3-178
4-172
5-170
6-173

wet
1-215
2-172
3-202
4-190
5-190
6-205
looks like my rings are shot beyond belief
and whats up with cyl 2?
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Old Aug 20, 2013 | 04:55 PM
  #2  
salad's Avatar
Herp Derp Jerp
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From: Parham, ON
Year: 1999
Model: Cherokee
Engine: 4.0L OBD-II
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Nothing wrong with those... if anything the test was done wrong. Factory service manual method is like this:

- Start with a warm engine
- Disable ignition and fuel system
- Block open throttle plate to WOT
- Measure compression on the THIRD stroke

Using this method a 4.0L in good condition will be around 120 PSI. The specification is that all cylinders should be within 20 or 30 PSI of each other.

If anything looks like you've got a top-end problem in cyl 2. Valve maybe.
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Old Aug 20, 2013 | 04:58 PM
  #3  
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From: Justin, TEXAS
Year: 1988
Model: Cherokee
Engine: 4.0
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opened throttle to WOT unplugged fuel pump relay, and coil wire, i think I measured compression on the third stroke, my understanding is there shouldn't be a huge difference between wet and dry tests?
theres about a 50 psi difference on cyl 1?

Last edited by 884x4; Mar 17, 2014 at 09:02 AM.
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Old Aug 20, 2013 | 05:18 PM
  #4  
Bustedback's Avatar
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From: Oroville, CA
Year: 1995
Model: Grand Cherokee
Engine: 4.0 with all of the noise and clatter
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How does it run? Good? Don't worry about it, just drive it.
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Old Aug 20, 2013 | 05:22 PM
  #5  
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From: Hainsville, NJ
Model: Grand Cherokee
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I would rerun the test for cyl 1 again just to be sure, but I agree with salad.
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Old Aug 20, 2013 | 05:44 PM
  #6  
884x4's Avatar
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From: Justin, TEXAS
Year: 1988
Model: Cherokee
Engine: 4.0
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the reason I did the test is because 1 qt of oil is disappearing every 100mi with no explanation. no leaks and im using rotella 15w-40 with napa gold filter
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Old Aug 20, 2013 | 05:46 PM
  #7  
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From: Havana fl
Year: 1995
Model: Cherokee
Engine: 4.0L
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could be valve guide seals. Do a leak down test and see if its rings or valves or what
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Old Aug 20, 2013 | 05:50 PM
  #8  
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From: Oroville, CA
Year: 1995
Model: Grand Cherokee
Engine: 4.0 with all of the noise and clatter
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Check and clean the CCV system.
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Old Aug 20, 2013 | 06:07 PM
  #9  
884x4's Avatar
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From: Justin, TEXAS
Year: 1988
Model: Cherokee
Engine: 4.0
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Originally Posted by Bustedback
Check and clean the CCV system.
new ccv everything about 3 months ago, zero oil in the air filter
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Old Aug 20, 2013 | 06:08 PM
  #10  
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From: Justin, TEXAS
Year: 1988
Model: Cherokee
Engine: 4.0
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Originally Posted by mentalbreakdown00
could be valve guide seals. Do a leak down test and see if its rings or valves or what
will do, thanks
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