Hi everyone, I had a couple of questions....I bought a 86 f250 2wd with a 302 efi from a police impound auction for 400 bucks, I got it home and I couldnt get it started no matter what I did. It also kept burning up battery cable and killing the battery, I changed almost everything, tps, ignition control module, hall effect sensor in the dizzy, cap rotor, wires, plugs, checked fuel pressure, fpr, high and low pressure pumps, map sensor, then I started hearing a funny hissing towards the back passenger's side of the engine, it would only hiss for about 5 seconds after I stopped cranking the engine....I discovered it was coming out of what used to be the o2 sensor, apparently the cats were so clogged, the exhaust pressure blew the porcelin out of the o2 sensor lol, so I plugged it, and cut the exhaust off and low and behold the truck fired right up! Soooo....I decided to time it and get it roadworthy, well thats my problem, the truck starts right up and runs great!!.....at an idle, as soon as I put it in gear it develops a miss and when I drive it, it cant get out of its own way.

So I checked all of my work, timing, firing order, connections, fuel pressure, yada yada, and then I rechecked it, and still the same thing, runnin bad with a miss. So now I'm thinking burnt valves? bad head gasket? Who know's...well I checked the compression this morning, and it was 70lbs on every cylinder, I checked it several times, now correct me if I'm wrong but shouldnt it be around 140 or so? Then I decided to do a leak down test, got the cylinders to tdc applied air and I heard hissing from the exhaust, so just for the heck of it I moved the crank a bit to see if maybe the air pushed the piston back a little, and it made no difference....another thing I heard, which was really wierd is a creaking coming from the other side of the engine, when I only had air applied on a cold engine, I know its supposed to be warmed up but after I got those crazy compression readings I figured the game was over anyway...but anyway, the noise sounded kind like when your engine is cooling down after shut off, tink, tink, tink....I have no idea what that is about, all I am sure of is that its not right, lol. I just figured I would come on here and see what you guys are thinking, I am pretty sure I have to start by pulling the valve covers, checking the usuall stuff, rockers, valve springs, push rods, etc...then if I find nothing I guess I will have to pull the head and see what the valves look like. Anyhow, thats my story and I'm sticking to it. Sorry about the long post, that was as short as I could make it without leaving anything out.----Jack

 

Plugged cats likely caused the exhaust valves/seats to get hot beyond their limit.
You may be able to get by with just doing a valve job with new seats, or you may need heads.

 

Did you replace the O2 sensor after you got the truck running? If not, then the computer doesn't know how much fuel to supply the motor.

 

Nope...I know it would make the truck run a little wierd but it would just default to the factory ecu fuel mixture, either way it wouldnt have anything to do with the crappy compression readings and failing the leak down test miserably lol....at this point I really wish it were the O2 sensor because I think this truck just became a parts truck!! lol Its ashame cause the truck is super clean but its not worth it to me to throw a motor in it or do the heads.....If anyone is interested in it, e mail me, its goin up for sale as a parts trucks right now.