sorry about being an E250, but with the gross lack of informed van forums out there im hoping that an F250 is close enough mechanically that i can find the answers here.



2000 ford E250 4x4 van. 5.4 liter engine, automatic transmission. in the mornings at start up it runs great. power is pretty dang impressive considering the weight im hauling around with a gas engine. the trouble starts once the engine reaches operating temperature. after 5-8 miles of driving (depending on how cold it is outside) the engine starts to stutter both while accelerating and while under load (cruising at highway speed then start to pull a hill). by "stutter" i mean it loses power, jerks a little while trying to accelerate, and feels like it would feel if a plug wasnt firing. im not getting any codes or errors from the ECM.

based on that it acts up after the engine warms up but runs fine while cold, im thinking its probably at least one of the four O2 sensors on the vehicle. as i understand it (and please correct me if im wrong) the ECM ignores signals from the O2 sensors until after the exhaust manifolds reach normal operating temperature (approximately 600 degrees). i dont know which of the four could be acting up, or how to diagnose them. since apparently mechanic shops have become so dependant on computers that they cannot diagnose a problem unless the computer is throwing an error code, i dont want to start paying someone to just keep changing parts until they find the problem.

any educated opinions on this would certainly be appreciated. im also down to 9 mpg where i should be getting 12-15.
thanks,

 

i replaced the two O2 sensors (at the exhaust manifolds) and the one behind the cat. sadly, it made no difference at all. once the van reaches operating temperature it starts to sputter. any suggestions appreciated.