The guys were loading up our 2001 flatbed for the job tomorrow, and something is bad wrong. Lots of white smoke and a really bad miss at higher rpms, especially while under load. Almost sounds like a knocking. No codes scanner at the office, checked the codes with the key trick and the only one that shows is p1693. No fuel pressure gauge, but it starts and idles like it always has. I'm thinking it may have dropped a valve seat, does this sound right?