I have an 04 F350 Crewcab Dually Diesel with 38,000 miles on it. About 4 months ago check engine light came on. Took it to a dealer they claimed EGR valve was bad so they changed it and fixed the recalls. A couple weeks later the engine started make a wow wow sound. Now the truck is making the sound more frequently plus bucking and spitting almost sounds like backfiring. You can usually drive about 40-60 miles before it starts acting up. Took it to the dealer and they found no codes. Told me they could not diagnose problem until check engine light comes on or truck completely dies and won't start again. Talked to another dealer and they told me the same. Can anyone help?