I had a tank of bad fuel go through. I know this because I changed the filter and found some (1/2-3/4 full) really horrible gunky water in it. I drained the tank immediately after discovering this, and there wasnt a whole lot of nasty in it. It is quite possible that almost the entire tank of bad fuel went through the engine. I began noticing problems in Montana, checked the prefilter and saw no indication of anything amiss, so I just kept going. I was pulling a trailer so it is quite possible that I burned a whole tank of bad fuel without noticing. I did not notice any adverse performance, but with the engine maxed out like it was, pulling the trailer, I dont imagine I really would have. Could be that a little watery fuel = the straw that broke the back of my 370K mi inj. pump? I guess we'll see someday, but I would love to know more about those delivery valves first! Thanks again for all the help.