I just purchased a 1999 4x4 4" lift Super Duty PSD. It has 320k and has been completely rebuilt before I bought it. It runs really good, but, when it reaches around half a tank it starts to act funny. It acts as though it is running out of fuel. Every once and a while while running at 70 mph and I speed up, it sort of feels like it is stuttering. It is not very noticable, but I can feel it. So in the mean time, I have to keep it full. When I fill it up at half a tank, it usually takes about 15 gals to fill it up. Any thoughts? Thanks, Mark.

 

You'll need to pull your fuel tank, Pull the tank module and check for damage or a pin hole.
I'm sure one of the Powerstroke guys will be in soon and give their opinion. They would be more likely to know if there's anything else thats known to be a problem.
I checked Fuel system TSB's and the only issue regarding fuel tanks was involving the two tank setups and water entering one of the tanks.
If your sure its only at half tank and below, I would probably look at pulling the tank, thats really the only area that can cause that problem. You'll be looking for damage from about the middle of the tank maybe a little higher! Modules really are not that expensive, might be the easiest way to go!

 

your pickup tube has either come loose or has a hole in it.... drop the tank and check it...

15 gallons is a half tank if you have a exCab SB, reg cab long bed, or (i think) a CCSB..... they only have 30 gallon tanks where as the CCLB and excab LB has the 38 gallon tank....

 

I have had a couple trucks doing this. One the sending unit was all ratty on it, and the other one actually had nothing to do with the fuel level, it was just a coincidence - the under valve cover harness was falling off on the left side.

Weird, I know.

I'd drop the tank and have a look see as to what's going on.

 

Thanks you guys. It is pretty much the same thing that I was thinking about myself. By the way, it is the crew cab short bed. I just wasn't real excited about the thought of having to drain out 20 gals of fuel, but oh well needs to be done. Again, Thanks, Mark.