2000 f150 v8 4.6liter. truck runs fine until about 40-55mph then starts running rough like it's missing but no codes,
Idles fine
Rough running only between 40-55 mph will smooth out after accelerating past 60

any help ??

Thanks

 

Sounds like a weak coil.

 

how would I know which one ??

 

I would get into that speed range and try to keep it misfiring until your CEL comes on and you see what code is thrown. The fault has to be active for a short time for the processor to throw a code. If a code indicates a misfire tied to a specific cylinder, you can swap the coil with another cylinder to verify. Don't go parts buying without diagnosing because other parts can also cause a "bucking" feel even the transmission.

 

when did this start? if it just now started then the truck probably hasn't thrown a code yet