So.... having an odd problem with my 1984 D50, 4D55T. It starts fine, and idles (very low rpm, lower than normal), and it'll even drive around -- very very slowly in 1st low range 4wd. But, it will not rev at all. Pushing the accelerator down gives zero results, as does manually revving it directly on the IP. When you very first start it it will rev for the first 2 or 3 seconds if you try, then back to low rpm idling. As if it has a little fuel reserve in the lines or the injection pump, but then can't get enough fuel. But it keeps idling really low and doesn't stall out, usually. Classic symptoms of a clogged fuel filter, so I just put a brand new on on. And NO change at all... what the heck? This started this winter when I ran either ran it out of fuel or gelled it or both -- oops. I parked it till it got warm and now I'm trying to get it running again. Anyway, I purged the system of air, and I am getting fuel at all four injectors when I crack them. But, obviously not enough. For a little while this spring after I purged the air and gave it new fuel it would occasionally rev, but now it will not at all. So... is there another filter somewhere I should check? Back in the tank maybe?

BTW, I do have an inline electric fuel pump as well and having it on or off doesn't make any difference.

I do have a spare IP if I have to, but if it's simply a different filter somewhere, I'd rather not get into swapping the IP.

Thanks

Zeke