That is a great question.
Mine to you is, how does #8 recoup the 120PSI to be close to the others?

I certainly can try but I dont see how it changes the solution?

 

Reading through, I was sure this was a valve or cam problem until you said it briefly hit 200 psi with too much oil in the cylinder. Sadly, to me, that points to rings.

But if that's it, they aren't so hard to replace. Especially if you aren't going to redo everything else.

Just being a hillbilly I would put compressed air in the spark plug hole for 8, then listen for a hiss at the tail pipe (exhaust valve not seating) and the intake (intake valve not seating). If inconclusive I would then drain the oil and remove the drain plug, to see if it sounds like it is coming from the bottom (rings). You might even feel some air pressure there. However, if you had massive exhaust blowing past the rings I'd think you would have oil being blown out of someplace like the hole the dipstick tube goes in, the front seal, or the rear seal.

So I'm not sure.

And are you sure it is not a head gasket? Recall that the hg can blow between cylinders, though I've never heard of it. If that happened I guess 6 and 8 would both have terrible compression, so that's not it. This is how I think. It's messy.

 

When i put the oil in I put far too much. When the I removed it from the pressure release it basically went back to 30PSI

 

I'm not understanding the pressure test, I guess. I'm getting that it hit 200 when it had oil in it and only 30 without. The oil would seal the rings, not the valves (jusy by gravity, though a small leak in the valve night seal better with oil splashed on it). No way you'd get 200 psi out of leaky valves unless the cylinder was full of oil. If the lobes are worn or you have a stuck lifter, the valves wouldn't open as much (because their natural state is closed, by springs), but that wouldn't cause low pressure.

Just thinking out loud here, but I think the move would be to drop the oil pan, squirt some oil in number 8, and rotate the crank or put compressed air in the cylinder. I bet you hear a lot of air coming around the number 8 rings. If that's not it then it has to be a valve, but I would be surprised at that.

Or am I misunderstanding the pressure result?

 

OK, yes I'm dumb I put way to much oil in. When I ran the test with approx a table spoon it was back to 30 psi

 

Oh dang, I did misunderstand, then. Sorry Buckeye.

 

As you may recall, I had a bolt on top of my piston. Whenever you think you made a dumb mistake, think of that...

 

I think the plan right now is to start tearing down until I get to the cam and get a look at it and the lifters. If it is not crystal clear as the issue I will remove the heads and so on...
Who makes the slightly hotter cam for the 4.0?

 

Crower. But they are slow as Christmas to ship. If memory serves it is the '229.

To get the cam and lifters you'll have to at least loosen the heads (more likely remove) to get the pushrods out. I've set the push rods with the heads hovering (on ARP studs) but with the head bolts on you'd have to overcome the springs to get the rods out and you might push a valve onto a cylinder (though I don't see how hand strength could bend a valve). Or you could just take the valve covers off and remove the rockers. But a caution there, I have a few sets of heads and each time I put the rockers on to tighten the rods, I stripped a bolt hole.

I've never removed the cam without removing the engine but I think it can be done if the radiators are out of the way.

You may recall I found a leaky valve (not the one with the bolt damage) by pulling the head and pouring water in it. I didn't invent that, but it works. So if you end up pulling the head it is a cheap test.

 

It's an interesting thought, but how does the car idle with the flap closed?