I have a f250(2004) with 30,000 miles and have a problem(s) the dealer has been unable to fix.

At 50mph the engine starts missing and has no ability to accelerate. I am also getting 9mpg(diesel). Dealer tried things unknown but has had the truck for weeks. Any ideas? Seems like too much fuel going to the motor. Dealer is waiting for a sensor but I don't think that will help. Any ideas how to tell the dealer how to fix my truck?

 

Check FICM harness for chafing. That would be my first guess. Does strange things sometimes.

 

Why do you think it is getting too much fuel? Is there a lot of black smoke coming from the exhaust? Diesels will not develop a misfire due to too much fuel they will just try to make more power. If there isn't enough air then they will smoke black. Like was said the fuel injector harness can get chaffed and cause a intermittent miss. Poor fuel could have damaged an injector or clogged one up. Does it matter if the engine is cold or hot? What kind of oil do you use, it could be foaming up if it isn't the correct grade.