Thanks everyone for the help.
[UnregisteredUser] not sure how i'd react if the plenum gasket is blown again, [not likely it could wet that plug enough to keep it from firing]

 

Haven't tore into engine yet, but have a compression gauge now.

1.What is a acceptable range for the 5.2?

2.what's best way to check reading...start, crank or turn by hand?

3.how long should it hold pressure?

4. if compression ok....does this rule out cracked head?


[I can't believe it's a cracked head, just because the amount oil that's being pulled into the chamber -so much it won't fire-......thinking of pulling exhaust manifold 1st to see if oil is leaking down valve stem]

 

Anything over 100 pounds is 'acceptable'......

To test, pull ALL the spark plugs, do one cylinder at a time. Have the throttle held all the way open. (disconnect the coil wiring harness connector AT the coil. Not the coil wire to the distributor mind, the connector that actually controls the coil, It doesn't need to be firing here.....) Crank the engine 5 or 6 revolutions per cylinder. Record the results. Post them here.

Pressure will probably bleed off pretty quickly.. but, the gauge should have a check valve in it, so it maintains the reading until you push the little button to release it. Don't worry about that, unless you stop cranking with both valves closed, there will be ZERO pressure. Not a problem.

Maybe. Yeah, nice answer huh? Run the test, post the results, and lets see what ya get.

 

Ughh.....

1-150 2-120

3-105 4-110

5-120 6-150

7-155 8-000


......nothing on #8

 

As in, no pressure at all on number 8??? If so, that's not good. (thank you captain obvious....)

Have access to a cylinder leak down tester, and an air compressor?

 

Big "Zero" on #8

have a air compressor [10gal] abt 120lbs.

No one with a cylinder leak down tester that i know of, gonna check with one guy that might.
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no leak down tester

 

Started the tear down...after removing the in-tank I looked down the TB and there's oil!!
I guess my 1st question, has anyone heard of Hughes kit gasket go bad? Next, is there any other situation which would allow oil to collect inside the plenum [taking into consideration of my "0" compression on #8]?


Note: Truck was driven home about 29miles after the misfire started-could oil be sucked back into the plenum thru the #8 port?

sorry for cluster of questions..........

 

You are the second person that had the hughes fix, that subsequently blew the gasket again. If that is indeed what happened.

As for the oil coming up thru the number eight cylinder, into the intake.... have to see just what is going on for that cylinder first. I don't think the just a blown plenum would accumulate that much oil, that fast on the plug, but, a holed piston might......

When you get the valve cover off, had a look at the valves and springs on number eight, and see if there is anything obvious there.

 

A bent intake valve could cause zero pressure and oil control problems, and could easily enough account for the oil. The bend would wear the valve guide quickly, so oil would be sucked through it on the intake stroke and some of that oil would be blown back past the incompletely closed valve into the intake manifold during the compression stroke. There'd be no tell-tale backfire because the spark plug is oil fouled, but I'd expect that there would have been a few backfires immediately after the failure and before the plug fouled.

 

Zero compression solved........oil in plenum unsolved. Don't know where the rest of #8 exhaust valve went, no damage to in-tank valve.

Number six looks like some coolant has entered, cylinder wall has a couple rusty looking patches-but they're smooth to the touch [#6 was a 150lb cylinder].
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I don't want to pull the other head if at all possible [was gonna look for another truck after firewood season]. However, #3 & #5 are 100lbs. & 120lbs. Is there any product that might restore some of the lost compression?