Ok. My dad owns a 1997 F-250 4WD 351W. It is a F-350 diesel according to the VIN, but is badged and titled as F-250 with a factory 351W. Confusing from the get-go! I am a mechanic, but a relatively new one (just graduated Nashville Auto Diesel College, but I am no stranger to this type of work) and his truck had me backed in a corner shaking in my boots, lol. He has been having fueling issues. He has had a lack of power, hard starts in the mornings (or after sitting at a job site all day), rich-smelling exhaust, strong gas odor while starting after sitting, and has had to stay in the pedal some to keep it idling. My first thought, pressure regulator! He bought it and I replaced it. Wha-lah! Fixed! For a minute... That was last week. Today he calls me saying the symptoms are back, along with some new ones. Now his rear tank is returning to the front tank, causing it to overflow. I know that this is a jacked up system with check valves, no selector valves . He said he replaced his front pump about 3 years ago, but I know Chinese Autozone parts suck, so it may the issue. I guess I'm trying to ask someone who knows this system thoroughly if I'm missing something obvious here, or if I seem to be tracking in the right direction. I do not want to waste his money throwing parts at it. Thanks in advance, FTE has always pulled through for me!

 

Fuel Module in the front tank is bad if it is allowing fuel to flow back into it while on the rear tank.

As for your stating issue, I'd suspect a bad Engine Coolant Temperature sensor. Try pulling codes.

 

That's what I was afraid of. He was adamant that could not be it, since it was only 3 years old. Dang Chinese!!

Codes are the first thing I go for in any diagnosis on an OBD I or II equipped vehicle. There were no codes present. I'll get out the pyrometer and multimeter next time I'm over there and test it and that circuit for any problems. Thanks for your thoughts!!

 

Please define that statement in bold. Did you get the System Pass/All Clear code of 111/111 or no codes at all? If the latter your test is invalid.

 

Also the temp sensors both air and water can be bad and not give a code as the computer has no way of knowing if they giving the right temp or not.
The KOEO self-test is just a electrical test saying that they are there or not.

 

Yes, I got the system operational code. I guess I should've said no trouble codes present!! I think I know the direction I'm going now though! Dad got fed up after knocking back a few refreshments, and started unhooking things, and when he unplugged "that big silver thing by the carburetor" (which is his idle air control solenoid on the throttle body we gotta love our dads!) he said the truck ran no different. So I think the IAC is starting to stick, or the pigtail is getting loose. I'm gonna check it out today. Oh and he's none to happy about having to do the front pump, again! lol