I have a 2006 d6r xw with the c9 engine. It started to stall under load. We thought it was freezing up due to the extreme cold so we put Melt down in it. Didn't solve the issue so after talking with finning we have changed fuel supply line ,regulator valve ,a transmission sensor, and fuel filters. It runs fine. Idles revs up fine a soon as it needs to work a little bit it will rev down to to 1500 1600 . It won't stall out now but has no major pushing power. I still think it's a fueling issue cause if it was a transmission issue it would be throwing codes. I also checked the tank for obstructions and even pulled the filter housing off to see if it had any obstructions. But one thing I've noticed is the first fuel filter the fuel goes to is always half full when we pull it off. The secondary is always full but can't figure out why the first one is running half full I'm told it should be right full. Any help or opinions would be greatly appreciated
just throwing it out there but have you checked the fuel tank breather in the cap Mark
Try the fuel supply line fittings right next to the tank. IIRC there was a fitting somewhere around there that had a lesser diameter than the rest of the line and was susceptible to plugging up if the dirt/water in the fuel tank wasn't drained on a regular basis. Even the ball valve to shut off the fuel supply line plugged if my memory isn't failing me.
Yeah we pulled the check valve out of the cap so it would be no chance of it being the issue