Just finished up a 5.4 swap into my 97 and have run into a problem. I think I have an idea of what may be the cause and want to see what you all think.

Compression on all other cylinders is between 195 and 205 PSI, #4 is ZERO. You can't even feel air blow out of the spark plug hole. Cylinder pressure is high because of a PI head swap onto a NPI bottom end in case you were wondering.

Connected my air compressor to the cylinder to listen for leaks and it held the full 120 PSI without losing any air. There wasn't any air escaping via intake, exhaust, past the rings, head gasket or anything. It just held the pressure.

So, here is what I am guessing, one or more valves are closed and are not opening at all. I am hoping to pull the valve cover and see rocker (follower), dead hydraulic lash adjuster etc.

I figure if the valves are closed that the cylinder can't get air in or out and cannot move air or build pressure.

Thoughts?

 

I had a similar problem like this with no compression in a cylinder causing a misfire. The engine was a 01 4.6L and I figured it was a stuck valve as well. My exhaust was doing a throwing air and sucking air aswell.

Pulled off the valve cover to find that the valves were good so I decided to just pull off the fuel injector for the cylinder. It turned out to be the connection to the fuel injector not being to so good since I would move the wiring and the misfires would go away then come back. I fixed the connector and it hasn't lost compression since.

But removing the valve cover is where I started...

 

pulled the valve cover last night and found the follower for the intake valve had fallen off. I also found that the intake valve was bent.

Why didn't my air test find this, because I used the hose from my compression tester which has a check valve in it. Felt pretty dumb when I realized that.

Anyway, head is coming off today and will get a new valve and head gasket installed. Hope to be up and running this weekend!

 

FYI Make sure that the valve guide is not cracked and that the lash adjuster pocket in the cyl head is not cracked as well. When this failure happens its because the lash adjuster was loose from either a defective lash adjuster or a repair was performed and the tech didn't get the follower tip completely back over the lash adjuster tip or a follower bearing or bearings went south. Check the piston as well for damage although with the 5.4 it may not have made contact. The lash adjuster pocket ( hole the lash adjuster sits in) can crack with this condition and be hard to see only to have it completely break out and you will lose oil pressure in that cyl head causing bigger problems. The cam lobe should be inspected as well...Good luck.

 

So this was an interesting discovery. Valve wasn't bent it had a piece of rag stuck on it! Guess it couldn't fully seat and allowed the follower to fall off.

 

Wow! That's an unusual problem.

 

That 's one way to wipe off the valve and seat. LOL