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Discussion Starter · #1 ·
chiltons doesn't show what the compression range should be for my 87yj 4.2L. it shows for :
92-95 2.5L = 120-150 psi
92-95 4.0L = 120-150 psi

the book covers as old as 87 but doesn't give compression for older than 92.

has all the other engine specs for the 4.2L except compression. go figure!
i tested and all 6 cyl's at 150 psi. no variation.

just curious if anyone has access to a list spec?

she's a tight one


4,520 Posts
yes a 150 psi does sound good.. what you are looking for is more of a variation between them.. if they are all 150, then all should be good. hence not all the rings should go bad at once.. one cylinder should be worse than another.. so yes they sound good..

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