I have a 1993 4x4 with a 5.0. i did a compression test and one cylinder has 0 compression, but the rest are up around 150 psi. The motor only has 143,000 kms on it.I was just wondering wether I should pull the head off this motor and see what is going on or swap in the motor out of my 1991 that has 225,000 kms on it.

 

i would pull the head and see, if anything is shot either fix it or swap the motor

 

Add some oil to the cyl and test compression again, if it makes no difference the problem is likely a burnt/broken valve so a simple head swap and you're on the road again. Of course you could have a hole in a piston too and that will give the same results. If the oil does improve compression then the problem is with the rings so an engine swap is probably the easiest thing to do at that point.

 

Thanks for the help i will try putting oil in the cylinder.

 

i tried putting oil in the cylinder and it did not change the compression. i also forgot to mention that there is gas in the oil. I did a leak down test and it wouldn't hold any air but i couldn't tell where it was leaking.

 

Well, unless you have a scope appears the next step is to remove the head and see why ..... either a valve or piston problem ....

 

would a valve put fuel into the oil?

 

Your dead cylinder may be putting fuel in the oil. The injector is still spraying a fuel charge into that cylinder, but if your rings or piston is shot, the fuel/air charge will not be compressed--it will just get pushed to the underside of the piston, where the fuel will mix with the oil in the crankcase.

Jason

 

Dont know if our Fords suffer this with the frequency of Chebbys, but the Chebby guys at work always talk about a dead cylinder because of a lobe worn down on the camshaft.

 

Is it the #8 cylinder? If it is then most likely the piston has been burnt/melted. A common problem on this year/engine was that the pcv is directed into the back of the intake and the gases dump into the #8 cylinder causing it to constantly run too hot. I had the same issue at 100K. I didn't have the $$ at the time to replace the engine. I wound up pulling the head and dropping the oil pan. I bought a new piston for $11 and a new set of rings (steel...not molly to seat better). I pulled the piston/rod through the top, honed the cylinder in place and dropped the new piston in.

It was a pain to do, but kind of fun too. That was 35K miles ago and I use the truck for plowing. It runs fine and doesn't burn any oil any more...nor does it run rough. I know the right way is to rebuild the engine and balance the pistons and all, but these 5.0's can take lots of abuse. The other thing you want to do is reroute that PCV from the back of the intake to the center vacuum tree (That's what ford did in later years).

You could find another 5.0 for the same year and it could have a weak #8 for the same reason.

 

That is an example of how bad the materials are inside those GM products, and it's something that simply doesn't happen with these Ford small blocks, all the castings, machine work, and fasteners are of much higher quality.

 

or it could be because of the tree huggers taking zinc out of the oil and people running agressive ramps on their flat tappett cams are losing lobes

 

It is the second cylinder from the front on the right side when standing in front of the truck. The motor in my other truck runs strong and i am going to test it first. I am figuring on it being less work to change the motor if this not the case then i will probably go the other. I just didn't want to get the head off and find out i have to pull the motor anyway. If i can pinpoint it to being a piston which i think is the case i will probably change the motor.

 

Why trash the block IF it's still in good shape. Hell, give it to me. I'll save it!

 

I had a similar issue with a 302 in a mustang (89 GT). I lost compression in the cylinder you did and the one in front of it. I was sure I cracked the cylinder wall. I pulled the head and the head gasket between the cylinders had blow apart. I am not saying this is your problem, but I would definitely pull the head (heads) before I made a decision.