I have a 91 F-250 with the 5.8 and I'm stumped. So far I've changed the TPS, the Coolant temp sensor, the fuel pressure regulator cap, rotor, plugs,wires, MAF, Fuel pumps check out ok, checked timing, and it's not throwing any codes. Everything has made a difference but when your going down the road, if you give it more than about a third of the pedal it dies. Runs great and revs awesome in park but when in gear you can run all day long if you don't give it more than a third of the throttle, any more and it just tries to die. I've all but had it and any more suggestions would be greatly appreciated.

 

you have a plugged cat my guess. pull the o2 sensor then drive it. or power brake it (don't spin tires) for few seconds, before and after. or test back pressure with a gage.

 

It could be a plugged cat..Pull the spark plugs,if the cats pluged, they will be Black.You can also check the temp of the cat..Check the temp at the front and rear of the cat,if there is a drastic difference in temp yea its pluged..I had the same symptom with a customers truck..I left my fuel pressure gauge on for a test run when it started acting up i pulled over and checked the gauge,it was low..Turned out the fuel tank was full of rust and debris..It was clogging the Strainer..My 2 pennies.

 

Thanks guys, I check those things when the weather gets better as I don't have a dry place to work on it.