i have a 1991 f250 with the 7.3L i have been running vegie oil. starting on diesel then switching to oil once warmed up. the other day i was stoped at the light then the truck started to surge from about 700 to 500 rpm i was wondering what could cause this any ideas?

 

possibly air in the lines, or your mechanical pump is starting to crap out. check fuel pressure going into the filter.