My girlfriends been complaining of bad mileage and a rough running truck lately. Last night, I ran a compression check on the truck (96 F250, 351, E4OD, 4x4). Cylinders 1 thru 4 were between 160psi and 170psi. Cylinder 5 was 25psi and cylinders 6 thru 7 were between 150psi and 165psi. So I think I found the problem, cylinder 5.

I can get a complete 351 (intakes, manifolds, everything) from a friend, which came out of a 93 F350 (E4OD, 4x4) for $100. Its got 131,800 miles on it. The first question I was wondering about, is everything the same? Are the blocks the same? I'm pretty sure they are. The next question, what should I replace or look for on this engine? He said it ran fine when he took it out. The only reason he took it out is because he dropped a cummins in his truck.

I plan on getting a complete gasket set and a new oil pump to put in it. Should I also get a rear main seal even if it aint bad?

 

WOWWW.... there cowboy? You have not yet completed your diagnosis and you're ready to replace the engine already!

For all you know this is nothing more than a bent pushrod. You haven't even so much as pulled the valve cover and you're ready to rip the engine out.

Put a teaspoonful of oil in number five and test the compression again. If it comes up, it's a bottom end problem, if it doesn't then it is probably a valve or some such and can easily be fixed with a valve job. There's no need to go ripping the whole engine out.

Thoroughly analyze before you act.

 

Agreed- you'd likely be going to a lot of unnecessary work. Do as Doc suggests and look into the problem further before opting to replace the engine.

After you've tested the compression again w/ the oil, if it's still low, try squirting diesel into the cylinder and give it some time to set. I can't remember how long at this point but I think it's at least 12 hours- if it's stuck rings the diesel may break them loose.

Besides, how many miles are on the existing engine? This is just me but I wouldn't swap the motor for one w/ 131k on it, unless I had plans to rebuild the motor first.

 

I have a bad habit of repidly perusing posts, missing important details. DBG obviously studies them closer than I do. I missed the fact that the proposed engine is not reasonably fresh. That makes the impulsive engine change even more questionable.

I'm not trying to belittle anyone, just trying to give good advice.

Good catch DBG!