2004 5.4L 3V with 90,000 miles. I kept having cylinder 1 misfires under heavy load. I eliminated plugs/coils/injectors by swapping them between cylinders 1 and 2. Compression was good (about 165 PSI) in cylinders 1 and 2. Leakdown test gave variable results (sometimes low and sometimes quite high through the intake).

I got the head off and am having the same inconsistent leakdown. I'm using a plate with holes for head bolts to seal off the cylinder head on the bench. I will often get high leakage until I tap the sticking intake valve stem, which makes it seat and stop the leakage. This is with brand new valve springs on that cylinder. It happens from time to time with either intake valve.

My primary suspect right now is excessive grit in the intake side. The valve seat and valve sealing surface look good, but the intake side of the head is full of soot and grit. I fear this is occasionally getting knocked loose and keeping the intake valve from sealing.

It's not obvious to me that replacing anything at this point is going to help because nothing appears to be obviously broken or out of spec. My plan is to clean the head thoroughly, replace parts that I should probably do anyway around 100k, and button it back up.

Any thoughts? What things should I replace while I'm in there (timing chain, valve seals, ???). I'm probably going to push this thing off a cliff if I get it back together and still have the problem...

Thanks!
fiz

 

Do a proper compression test. That's right after shut down. Write down readings of ALL cylinders for comparison. Without that, 165 means nothing except they are sealing. You could have to much compression for that matter. Depends how you went about it. Without comparisons of all 8 it's to difficult to judge.

 

I did all 4 on the passenger side and got 160-170 PSI.

 

I would properly and thoroughly clean the valve stems and guides and replace the valve seals. Strip the head down and do it right or buy a rebuilt head.

 

did you ever get it fixed? i have the same problem