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Old 12-15-2009, 10:27 PM   #1
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YJ 4.2 motor ?s

Just wonder why the motor has compression issues in the 5th cylinder. Is what the guy told me.
I just bought this so I haven't messed with it much.

The Jeep will run just ruff it pulled it self on the trailer fine.
I guess it blows oil out the valve cover vents? again what the guy told me.
It has a new motor just sat for two years.

Is it a valve issue.

Any advice would help

It's a 88 4.2 auto

If you need more info ask and I'll get back with you guys

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Old 12-15-2009, 10:40 PM   #2
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This is what I found, I hope it helps.
Jeep Wrangler Engine Just Gave It Up

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Old 12-16-2009, 04:09 PM   #3
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Quote:
Originally Posted by 89PBR96 View Post
Just wonder why the motor has compression issues in the 5th cylinder. Is what the guy told me.
I just bought this so I haven't messed with it much.

The Jeep will run just ruff it pulled it self on the trailer fine.
I guess it blows oil out the valve cover vents? again what the guy told me.
It has a new motor just sat for two years.

Is it a valve issue.

Any advice would help

It's a 88 4.2 auto

If you need more info ask and I'll get back with you guys
did u put a compression gauge on the 5th hole? you need to find out if compressions low or absent all together
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Old 12-16-2009, 04:13 PM   #4
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A simple valve job could fix the issue. Maybe the intake or exhaust valve is cracked. Do a compression test as already said.
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Old 12-16-2009, 04:40 PM   #5
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If the motor has sat for 2 years it could be stuck rings. Put some kerosene in that cylinder let it set over night. Blow out the excess put the spark plug back in fire it up let it run and see if it comes out of it.
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Old 12-16-2009, 04:48 PM   #6
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If the motor has sat for 2 years it could be stuck rings. Put some kerosene in that cylinder let it set over night. Blow out the excess put the spark plug back in fire it up let it run and see if it comes out of it.
Kerosene or ATF..... It would help swell the seals but not a for sure fix.
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Old 12-16-2009, 08:20 PM   #7
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i would def. do a compression test fist ,but it sounds like a valve issue to me.
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Old 12-16-2009, 09:35 PM   #8
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PBR96;
Is this the one you bought for the hardtop and full doors ? You could always sell it with a soft top as a mechanics special. How good is the body / frame? If they aren't above average it wouldn't pay to go through with a transplant.
If my YJ doesn't come around with the latest addition of parts its good by Chrysler, my first and last. If I had the patience a GM drive train would be the answer. Famous last words...... And I thought ATVs were expensive !
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Old 12-16-2009, 09:59 PM   #9
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PBR96;
Is this the one you bought for the hardtop and full doors ? You could always sell it with a soft top as a mechanics special. How good is the body / frame? If they aren't above average it wouldn't pay to go through with a transplant.
If my YJ doesn't come around with the latest addition of parts its good by Chrysler, my first and last. If I had the patience a GM drive train would be the answer. Famous last words...... And I thought ATVs were expensive !
I want to keep it really and have two the body and and frame are awesome actually better than when I started on my 94

I'm am really leaning towards the valve but not for sure haven't had time to diagnose the motor yet

Thanks guys Keep the options coming
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Old 12-18-2009, 04:32 PM   #10
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So far I have found that if I pull the 5th plug wire it runs the same if I pull any other one it dies trying to find my compression tester and going to try that what should the psi Be 100 to 150 thanks guys
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Old 12-18-2009, 05:03 PM   #11
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Do you have spark on that cyl.?
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Old 12-18-2009, 05:08 PM   #12
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I'll check but I'm sure it's there

I drove it around the block and the valve cover was smoking out the breather and filler pretty good not sure
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Old 12-19-2009, 02:21 PM   #13
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It has spark the rotor and cap and plugs and wires are all newer

I pulled all the plugs some are all black and two are white on the tips still I'm confused on this I can't find my fitting for the compression Waiting on a buddy that has the right line to test still

But I want to address the plugs also

Thanks guys
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Old 12-19-2009, 04:27 PM   #14
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Ok I tested the 5th cylinder and it has 90 psi jeep will run testing the 5th so I pulled the third plug and tested it jeep will not run on this test but has 100 psi so
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Old 12-19-2009, 05:31 PM   #15
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Retested it the cylinder by just cranking the motor over and 5th reads 30 psi and 3 still reads around 100 could this be simple as a valve or something worse never done anything like this before
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Old 12-19-2009, 07:56 PM   #16
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time for a leak down test or if you can find/make the adaptor you can fill the hole with 100 psi and see whats leaking
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Old 12-19-2009, 08:05 PM   #17
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Tomorrow I'm pulling the valve cover and my Step dad is going to help me out a little since he has done this before I'm kinda going at it with my pants down at the moment I really like the help you guys have offered I might no a little more tomorrow thanks
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Old 12-20-2009, 11:29 AM   #18
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I am not familar with the valve trane on the jeep but if the valve is to tight it will cause a low comp. and cause the crank case to build up pressure and then you see the smoke or the blow by as we call come out the vavle cover. Check to see if the valves are adjustable. hope this helps

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