low compression on 96tm 4.0 OHV

[stamina]

i put a 1996 OHV block and heads in my ranger when i did the 2.9-4.0 swap, engine had very high amounts of cylinder wear, could catch a nail on every cylinder, particularly cylinders 3 and 4. put new rings and lapped the valves nicely as it was my only option and it was dirt cheap. the rings have broken in and seated over the past 3 months (probably in the first couple of drives). i have now done a compression test as i have been having a progressively worse sputtering issue from day of the swap, if the truck is driven very very GENTLY it will not bog out, but it sputters BADLY if the revs are even the slightest bit too low from this perfect “GENTLE” spot that i mentioned earlier when taking off in 2nd, which the 4.0 is very capable of especially with the 2.9 low gear trans and 4.10. also when you give it any it just misses a LOT overall in 3rd or 4th, it bogs badly,i have tested everything else, it checks out, my results are as follows

1. 160 psi
2. 155 psi
3. 140 psi
4. 65 psi
5. 140 psi
6. 150 psi.

but wait, there’s more. this is the important bit. removed drivers bank cylinder head, there was large crack in between exhaust and intake valve, got junkyard explorer 96tm head that was in very good condition, installed. this has boosted the compression to 90 psi, i have let her run for a month since and it is still a steady 90. is it time for a new shart block lads?

 

[RonD]

Do a WET test on #4, should go up to, or above, 150psi if its a ring issue
If it just goes up to 130psi or so then valve is leaking in #4

 

[stamina]

Do a WET test on #4, should go up to, or above, 150psi if its a ring issue
If it just goes up to 130psi or so then valve is leaking in #4

ok i will get back to you with results

 

[stamina]

Do a WET test on #4, should go up to, or above, 150psi if its a ring issue
If it just goes up to 130psi or so then valve is leaking in #4

i tried a wet test, made sure to redo the dry test first a couple times to confirm.
dry: just over 90
wet: about 98/just under 100
tried the wet two separate times about 20 minutes apart about same result? is it another valve issue with this head in the same cylinder? i think im going to get a new casting cylinder head for christmas, if it fixes it, excellent, if not, ill use it on my next 4liter
also got rid of the bucking and sputtering by changing the stock SP486 motorcraft plugs out for iridium NGKs, made it run completely normal. but compression is still low.

 

[RonD]

That's a valve issue, per WET test

If you have a compressor you could push some air into cylinder 4 and listen where is comes out, i.e. tail pipe, intake or dipstick tube