I have a dead #7 cylinder on my 5.9L Shelby. First off it is getting spark, it is getting fuel. I put a scope into the plug hole and the piston does not have a hole in it. My first guess was I had run it too lean and it blew out a piston. I now know it did not do that, although I still beleive the truck might be too lean, but that is a different issue.

I ran a compression check on all cylinders to find out it was #7. All cylinder exept 7 run at 160-170 dry and cold. NOw #7 is doing wierd things, the first time I tested it, it showed as having 130psi, the second time it showed 0psi. So I tried to put some oil in the cylinder to see if it might be blown rings, first time it went to 120psi, second time only to 0 psi, and the third time to 40psi. So now I am at the point where I do not beleive it is the rings or a piston problem, and I am releived to find that out.

Now I am at a crossroad, I have yet to remove the valve cover to look at the rockers. The engine is supposed to have roller rockers on it but I have not confirmed this yet. Am I to assume it is a burnt valve? But if that was the case wouldn't it be 0 compression all the time? So I am thinking that maybe a valve is sticking open. Is this possible? I did not see any damage to the piston so I do not beleive that a valve I bent, so my only explanation I can think of is a sticking valve! Maybe a messed up seat, I dond't know for sure.

Is there anyone that has had a similar problem? The heads are mopar performance heads that are supposedly ported and polished (again I have not confirmed the ported and polished part). before I go anyfurther in disasymbling the top end I would like some advice.

Am I just stupid or is there something major I am missing.

(Also I am most knowledgable on small foreign four cylinder overhead cam engines, this bid as thing is completely foreign to ME!)

 

Sort of sounds like it's in the heads. Stuck valve, broke valve spring or something on the valve seat. If the rings would be gone you would have crank case blow by. That oil would be going back thru the pvc (check it for oil) into your intake. then you should be smoking as the other cylinders would be burning the oil. I know because I have lost my rings in the original motor. Also if the rings are gone you wouldn't have pressure one time and not the next. When the rings go it's over for them.
Check you PVC for oil for crank case blow by (rings) and pull the valve covers. I don't think it could be a rocker as it only opens the valve. Do check the springs. After that you might have to pull the head.

 

After removing the valve cover I immediatly noticed that the rocker had come loose and was just barely on. The nut holding it on somehow wiggled itself loose and was just about ready to fall off. Once I finished it started up and runs great. It seems it has been getting loose for a while because it definately runs a whole lot smoother now.
I can't tell you how happy I am it was something so simple, I did not want it to be out of commision for a long time.

 

glad it was something simple

 

Glad to hear that it was an easy fix. Sounded like a valve guide to me.