I have a '93 f-150 with a 302 and auto tranny there is about 143000 miles on it. I dont have any compression in my drivers side rear cylinder. Only about 30 psi actually. I pulled the valve cover off and dont see a broken valve spring. The spark plug is wet with oil. The pickup still runs ok untill it lugs a little then it shakes. Any ideas on this? Am I looking at a cracked ring or what?? Thanks for any help!

 

You can try squirting some oil into that cyl and see if the compression comes up. That might indicate you have a ring problem. I had zero compression on nbr 8 and no rise in compression when I added some oil to the jug. I pulled the head thinking I was looking at burnt valve, but it turned out to be a piston/ring/cyl issue on the high side of the jug so the oil didn't help. Mine ran pretty well until you started to pull power and then it chugged pretty good. I ended up putting a long block in it. Hope this helps. Good luck.
Steve 92 f150 5.oL 4x4

 

Burned pistons and valves are common on these V8's because of the PCV valve routing to the intake manifold. The PCV dumps directly into the intake runner for the number 8 cylinder, which causes problems like what you are experiencing. The vacuum line can be re-routed to the main vacuum tree, which will evenly distribute the crankcase gases to all the cylinders.

 

I have the same symptoms on my '92 with the chuggin and missing under heavy throttle. BUT, #8 gave me 215 PSI compression. Lowest I had was 190, on #2. Not bad for 137K. I've chased every fuel delivery and ignition issue I could think of. Found some vacuum leaks on the plenum which I've repaired, but still, the infernal heavy throttle miss. All the plugs are dry, perhaps TOO dry. No soot or ash at all.

I'm leaning toward a fuel pump caving in on me during high demand or possibly constipated kitties (cat converters). Light throttle/idle, no problem. Runs sweet. Just when I start climbing a hill, about half way up (obviously depending on grade) it starts with the spittin and sneezing, then develops a dead miss. It's my daily driver, so can't afford to have it down for any extended periods. I really don't think I have any ring issues. It'll go 4000 between changes and not lose a drop of oil. Don't think it's head gasket either, should have shown up in compression. Still need to do a leak-down, but that appears to be a long job, and I haven't had the time for it.

When I do get a leak-down rig, any thoughts on doing the leak-down cold? Hot cast iron is no fun. Like I said, I'm certain I don't have ring issues, but haven't ruled out valve issues yet. That's a lot more expensive fix than a fuel pump too. When I pulled the filter a few weeks ago, there was a lot of gritty crap coming out of it. If there's grit in the inline filter, it came through the pump. Pump still puts out 40 PSI engine off, and 30 PSI engine running, but I have to wonder about volume capabilities. Then, there's the 3rd possibility of crap in the screens on the injectors if the inline filter didn't stop all of it.

Getting absolutely no codes except 11's meaning All Systems GO!. I just wish the truck would GO!

Thanks in advance.