Never checked the tank strainer, could be it. There is some black particulate stuff in my prefilter, but not a whole lot. I have run 4 tanks of diesel through it since the problem began (road trip pulling a trailer), so I'm pretty sure it isnt bad fuel. I have also run a whole lot of lucas (like half a quart or more in each tank) and some howes meaner diesel cleaner in these tanks of fuel (just in case).

So, it appears the IP works, right? What about timing? Could the timing be an issue (veg cetane = something like 60, diesel = 40ish), therefore, if the timing was off wouldnt the veg run but the diesel not? My veg tank is full now, but I'll try running on a can of diesel to see if its the tank screen or vent. However, I don't think it is because I can still lay a healthy cloud of black smoke when I hop on it, and the power at speed was decent until quite recently (literally the last 200mi of my trip) If there was a fuel supply problem, wouldnt it be worse at higher load? Also, I think it is a diesel FUEL specific problem, because I have to wait a little while after I switch the feed over to veggie for it to run right, i.e the diesel has to circulate out of the pump. If it were a clogged screen somewhere the problem should stop right when I flick the switch (thereby releasing the vacuum), right?

The DIY method for start of delivery timing seems kind of hokey to me (pump the hand pump and look for about 1 drop per second), is there a better way to do it? Is there something I'm missing? Would a worn rack damper screw cause these symptoms?