I have a 8.1 Workhorse in a 2004 Scottsdale (Newmar) 38'. In any mild rain, could not climb a grade or go over 40 mph withou engin missing. The more rain, the worse it got. Scottsdale suggested that the dealer put a splash guard of galvanized sheet metal between the right wheel and the engine. Did absolutely no good. Workhorse told the dealer to install an extension on the air intake so that it was up behind the cowl instead of behind the grille. Workhorse said that the problem was water getting into the air intake. Hogwash!. Intake was dry and so was the air filter. Mycar mechanic said that it sounded to hm like bad plug wires or ignition coil (Unit doesn't have a distributor cap). Each plug wire has its own little coil and replacing all 8 would be rather expensive. I took the cheap way out and just replaced the wires. Wunderbar! Came thru a trash movin' gully-washer of a rain storm with nary a buck!
