If I suspected what you did I would put an injector out in the open and see if it was spraying diesel at cranking rpms. That would perhaps either eliminate or give you some indication of what you suspect. I think a large shop would hook up a pressure gauge on the line but an injector spray test should indicate well enough. The only other variable I can think of is if you have two fuel supply systems and there is something drastically wrong in the diesel one. It must be fun to attempt to drive on diesel to say the least. I also want to mention that if water is in the fuel and processes through the pump we were always told it acted like fine sandpaper or a lapping compound. Could your alternative fuel have had had water in it? If you change pumps and continue with your vegatable based fuel you might want to incorporate a water separator in you fuel circuit. Not hard to do.