Ford V-10, OBD II Error Code PO 191

I also went through this issue. There is a TSB for this code and the code needs to be active when doing TSB checks. As I remember, there are three different corrective actions for the code with fuel pump replacement being one. The other two checked okay for me and the TSB recommendation was to replace pump. I had this done and the code problem was corrected. The clock was around 77,000 miles when the pump was replaced and is now about 103,300 miles.

Fuel pressure is probably falling out of spec intermittently. A shop fuel pressure test won't show this, only a road test will but the code won't appear randomly and the sender rarely fails . You probably need a new fuel pump eventually, but at the same time, if you are not having drivability problems, keep driving!

My only suggestion is to start carrying a 5 gal fuel can and a large rubber mallet to hit the tank with. If the fuel pump ever overheats and loses power while driving, some cool fuel will usually get you to a safe place to let things cool. The mallet will get you started a few times if the pump seizes and won't restart.

My '94 needed a new fuel pump, but I drove it 60,000 miles from when the symptoms first started to when I finally ended up ponying up for a new one.

Here's one reference, not fuel pump but fuel pump module (on an F150):

http://www.f150forum.com/f4/truck-stalls-code-p0191-fuel-rail-pressure-sensor-answer-46367/

Might check with a Ford dealer to see if any of the tech bulletins apply.
Tech bulletins