The afc is on top of the injection pump towards the rear. It has a foot in it that as boost builds slides forward and allows the governor arm to follow the face of the fuel plate which in turn moves the fuel rack supplying more fuel to the injetors. More than likely if you have a problem in that area it will be the little boost line that comes from either the head or the turbo over to the fuel pump.

 

Ok, I got a pressure gauge in line and at idle I couldn't get a reading, it was bouncing all over the place but as I increase the rpm the reading drops to zero. I also tried the pinch off the return line trick and the truck ran alot better. So I thought everyone was right about the return valve. I change it and there was no difference. So I thought again that it was a problem with the lift pump. I removed it and found some crap in the screen filter in the inlet side. I cleaned it out and went back to the truck and pulled off the pre-heater thing that is right beside it. I pulled off the bottom and found another filter (a screen type) and it was absolutely packed solid! Before taking this apart I tried blowing through the rubber hose that goes between the lift pump and the pre-heater and I almost couldn't. Now I know why. I plan on replacing it tomorrow. I'll update then.

 

keep us updated on the progress

 

Well, I changed the pre-filter screen and everything straightened out instantly. The truck runs smooth and strong all the way up to top speed. Thanks for all the suggestions. It's finally fixed.

 

atleast it was a cheap fix. I truthly didnt even think about the prefilter.