Information: 91 F150 4x4 302 112,000 miles.

Problem: Knocking when cold but not hot. Also, every once in a while there is a rhythmic loss of power, like one whole cylinder isn't firing or getting gas. I've disconnected the PCV valve from the air box and ran it to a rigged oil reservoir underneath. I go through about a quart of oil a week: blow by. What can I do, besides rebuild, to make this truck last a little longer?

 

You're losing a quart a week to blow-by?! Hate to say but you've either got a hole in a piston, or your rings are shot. That engine is toast. The knock you're hearing is probably a rod main.

 

i was going to say try seafoam and chek EGR tube... but... damn! a quart in a week ? mine doesnt go true any oil in 6 months ! and it has 256.000 miles on it,

 

The only thing I know to do to prolong the inevitable is to drain your oil, and refill it with about 75% Lucas Oil Stabalizer if you are losing that much oil. Do a compression test on your cylinders to see if you have just 1 bad piston or if they are all shot.

 

pretty good chance that there are two things going on one as said you probably have weak rings and two probaly cracked piston skirts !I have had the same trouble on previous engines and these are the things that I have found !Let me ask one question what type of oil filter are you using if its a FRAM take it off and replace it with an FL1A motorcraft and top off the oil FRAM will make cause the knock you are talking about something about the check valve in the filter !I had a 1979 F-150 with a 300 6cyl that had so much blow by that it would blow the dipstick tube out about halfway I remedied this by hose clamping a piece of rubber fuel line to the dipstick tube and inserting it into a gallon antifreeze jug tied to the fender and dumping it back in a couple times a week while I was building a 302 to go in it!

 

I figured the engine was shot... My problem is, I have an option to buy a 90 F-150 351 with the same number of miles on it. The passenger caliper is fried, something is wrong with the steering column, and when I opened the door, the handle came off. 500 bucks. I figure it'll last me a year. But I don't have any money right now, so my financial backing only comes in the form of buying a diesel or a rice burner. I'm not looking forward to leaving the F series behind, so I have ot make this truck last.

 

Hell mine got so bad in my 1990 f-150 302 that before I replaced it i burned a quart of 90 weight a day. Put some 90 weight with the other oil when you change it.

 

You may or may not postpone the inevitable of that truck giving up the ghost. Find another motor that is in okay shape and replace it or rebuild. Either way that motor has seen its best miles by the sound of it.

 

Buy this one, and swap the engines. It's pretty easy, plug and play. Use the computer from the 351 truck to make it run right.

 

I bought it... I figure it might be easier to throw the good parts of the 91 302 into the 90 351. Thoughts?

 

I'm all for the lucas oil stabilizer. I had a truck that burned alot of oil. I used about 75% lucas & as I lost it I just refilled with lucas, essentially 100% lucas after a couple of months. I kid you not, that thing quit burning oil. You should try it and see what happens. If anything do it just for kicks.