I have a 2006 F-150 4x4 with the 3-valve flex fuel 5.4L engine. In November 2013 the truck started cutting out. No Check Engine light ever came on, but using a OTC #3109 OBDII Scan Tool, I discovered that the fuel pressure was bottoming out to below 10psi. Based on the advice of this forum, I replaced the Fuel Pressure Driver Module. My problem was gone until recently.
When operating at low rpm (around 1200) on the highway, and the load increases, such as climbing a hill, the truck will again stumble. Again, I have no engine light. Plugging in the scan tool shows NO drop in fuel pressure. However, the Fuel System Loop Status changes from CLOSED to OPEN.
Everything else is within normal parameters as far as I can tell. What could be causing this, and how do I fix it?