1993 4.0l v6 ohv compression issue

[93rangerxlt-ca]

Im having an issue with my 5th cylinder. Seems like a stuck valve . ive read in the forums that the intake manifold gasket is an issue with these engines, is that possibly the issue or do i need to replace the head?

 

[93rangerxlt-ca]

Also fuel rich which takes me back to the intake gaskets not properly sealed. This being my first ranger im in need of experienced ideas

 

[RonD]

Welcome to TRS

Whats the problem with #5?

Yes, lower intake bolts are only 18ft/lb and can back out, using lock-tite and re-torquing can fix that.
Leaking lower intake would show Lean on spark plug, and if cylinder was misfiring then that whole bank would run richer, so pull spark plugs and have a look

Valves were never an issue on the 4.0l OHV, not that it couldn't happen.

If ever overheated, the heads would crack on these, causing misfires and coolant to be pushed out into overflow tank, and then more overheating.

4.0l engines also like Motorcraft or Autolite spark plugs, other brands don't seem to last very long

 

[93rangerxlt-ca]

Im showing bout 125psi and its never been overheated. And running rich on the fuel side. Do u believe that might be my problem? If so i wont bother replacing the head

 

[RonD]

125psi could be fine, depends on what the other cylinders tested at.

Cold engine
With all spark plugs removed
each cylinder in a 4.0l would be about 155-165psi with a calibrated pressure gauge.
With all spark plugs out starter motor can get good crank speed, we are dealing with a metal to metal air seal, so for sure not air tight, and it isn't suppose to be.
So slower crank speed allows more air to get out which lowers compression numbers.
Like adding oil increases compression numbers, blocks more air from escaping passed the rings.

And gauge could be off, doesn't matter if you are testing all the cylinders, because all would be off by the same amount, and compression test is not strictly about a high number, its about comparison of the numbers, if 5 cylinders tested at 130psi and #5 at 125 then all is well, then I would check the gauge, or timing chain, lol.

If you just test one cylinder and leave other spark plugs in then 125psi could be fine.

If you can test the others and #5 is low then add a teaspoon of oil thru spark plug hole and retest.
It will always go up, but how much it goes up will tell you if rings or valves are the cause of lower compression.

 

[93rangerxlt-ca]

Ive tried the intake gasket fix and what youve said before attempting the head replacement and i need to now