4.0L low compression question

mmmkay325

Well-Known Member
Joined
Jul 16, 2005
Location
Waxhaw
Ok, I'm in the beginning stages of determining why my 4.0L I6 has low compression. I have a 93 xj 4.0 in my yj with unknown milages...been running the engine for 1.5years with the same issue. I originally thought it was my tranny going out, but because the motor was bogging down so much on hills I thought I'd check the health of the motor.

I did a basic dry compression check on and my results Front to back 102, 105, 100, 80, 105, 90psi.

I think put some seafoam in the intake/vacuum line to try and free up some sticky rings but no real such luck.

Second dry compression check after seamfoam.

90, 100, 102, 110, 112, 100

I then did a wet Compression test

124, 151, 130, 142, 135, 130

Does this mean my rings are done or something else?? I'm just wondering why all the cylinders are so equally low??? Does that the mean engine is just that old/worn. If so is there more I should be worried about than just rings? I still am wanting to do a leakdown test to see if there are any other issues with the motor before I tear into it. Just looking to see if anyone has any tips or advise.
 
Ok so i've tried the "poor mans" method of band-aiding the bad rings. Dumped in some Rotella 15-40w and some RESTORE in there. As far as I can tell the motor still sucks and needs to be replaced/rebuilt. I haven't check'd compression to determine if the heavier weight actually helped or not, but it still feels like it's lacking some serious power.

Now I'm either thinking rebuild or stock replacment. Whats a ballpark cost to rebuild a 4.0 I6??

I've read the threads about strokers and the cost...but I'm just wondering what the average joes that does the work himself pays for a stock 4.0 rebuild. I just want to make sure i'm not getting in over my head. I'm sure this motor has 200K plus miles so I would probably do a full rebuild.

If the rebuild is too much I'm thinking it might be cheaper to find a cherokee with a healthy motor and just go ahead and get the aw4 I want also
 
If the motor needs to be overbored, which it probably does, then I don't think it would cost hardly much more to do a basic stroker.
 
drkelly said:
If the motor needs to be overbored, which it probably does, then I don't think it would cost hardly much more to do a basic stroker.
Click to expand...

From what i've read about the 4.5-4.7l strokers....most guys are usually looking at $1k+ depending on what kinda of parts they use. I've got it in my head that before I spend that on a 4.0....I'd start looking into the 5.3l and open up my wallet in that pit. I dunno know....really i'm looking at a way to fix/replace this motor for $500 and less. So that's got me thinking about picking up a complete cherokee and being able to use the tranny tcase etc and just sell the rest of it and not be too bad off in the money department.
 
Bearing set and Rings - its the 1st site i found.
main bearings: $90
Rod Bearing: $25
Rings: $50
Gasket set: $95
Machine work to bore: depends
To do a stroker, can just pick up a used 4.2 and you will have all the parts.

Basic low budget recipit would be 4.2 crank, 4.2 rods, and 4.0 pistons. We did it to my friends YJ and it moves. Still needs some work done with fuel, intake and exhaust to get the full potential but he drives it daily now.
 
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