I have a 90 F250 SC 4x4 5sp, 4.11 with the 351. It has 175K on it. I bought it a year and a half ago. Several months ago, the engine started acting up. It had no low end, would miss at idle, and would not rev well. By this, I mean it would scream at 2500 RPMS, and at 4000 it would sound like it was going to come apart. I could not rev much past 4000. It used to rev smoothly and not balk at higher revs. The tach goes up to 6000 with no redline. Check Engine Light has not come on.

So, I just installed a reman long block from Autozone - figured that'd solve the problem. Same Fuel Injection, same external components and sensors. the engine started fine, and I'm breaking it in. I now have about 200 miles on the new engine. Problem: It is doing the exact same thing! I can tell the engine is good (no funny noises), and I have better low end, but it misses, doesn't rev well, and is a total dog - very embarrasing on steep hills. It bogs as I press the accelerator, and just gets louder, not more powerful.

Ive checked and reset the timing (10 deg BTDC), new plugs, plug wires, dist cap, rotor. I am currently on my second tank of fuel injection cleaner with no improvements.

Where should I look? Anyone have the same problem? Dirty injectors - professional cleaning req'd? The timing does advance with the spout connected. Do I have a bad MAP Sensor? Bad Computer? Vac lines all seem to be connected. Haven't checked manifold vac yet. Air Cleaner is clear. It starts fine, just runs like a dog.

If this was carbureted, I would rebuild the carb, mess with the jets, and be sure the dist advance worked well (mechanical and vacuum) - I'm lost on the F.I. vehicles.

I don't want to have a brand new engine that still runs bad........

Thanks for the help!

 

Have you pulled the codes? Just because the CEL is not on doesn't mean there aren't any codes.

 

No, haven't yet. Would that tell me if I have a bad MAP, or dirty injectors?

 

it will tell you what the computer thinks is wrong. did you check codes before you pulled old engine? have you had the cats checked? get a vacuum gauge it tells a lot about engine shape.

 

Jarch I just fixed a similar problem. I read a post hear the other day about seperating plug wires #7 & #8,By the way it got worse just last week after changing plugs and wires. Go figure I could'nt belive it was gone.That embarassing pulling the trailer up a grade thing, no more and guess what now? I can do it with the A/C on . I use to blame it on being a 5.0L (W/3.55's) but now its acceptible.