my brother bought a '97 f150 4.6 a few weeks ago with a missing cylinder. it is cylinder #8 that is missing and he tried changing the spark plug wires, coil packs and switched a fuel injecter around with a different one and that cylinder is still dead. we did a compression test on it a few days ago and it's at 30psi. #7 has 150psi.

we haven't got around to doing a leak down test yet. there is no smoke or knocking or pinging coming from the engine both at idle and while driving. there was no oil registering on the dipstick when he bought it and the coolant is very clean. the temp guage also warms up like it should and stays constant at all times while driving.

of all of you guys that have seen/heard of problems like this, what exactly ended up being the problem.

it is cylinder #8 so i'm thinking that there might be a chance that the camshaft may have broken. i've heard about it happening on dodge v6's from the '90's. i'm guessing that it could also be a burnt valve, stuck valve, bent valve, hole in a head gasket... if it was a piston ring problem wouldn't that cylinder be getting oil on the spark plug and/or causing oil to get into the exhaust and smoke?

ideas anyone?

 

I'd lean towards stuck/burnt valve personally. Gotta check leakdown next to be sure.