My 93 f250 will only start off my rear tank. Initially it would not run at all of the front one. I bled it at the filter and now if I start it off the rear I can get it to run, although it is real sluggish off the front. Any idea what would cause this. A little background on the truck, I bought it from a friend of mine who ran it dry off the front tank and then only used the rear, that was about 3 months ago and I have bleed the fuel system by using the prescribed method I saw posted on here. It has been sitting with a full tank since then in the front. Is it possible the diesel in it is just bad or is it more likely that it has clogged lines in the front tank. Also when it does run off the front it idles at 500 rpm and about 650 rpm off the rear. It just seems weak like it wants to die of the front tank. Any help would be greatly appreciated.