Was driving last week and noticed a loss of power at 60mph. Truck would struggle to get to 70mph and would surge bad. Once off highway noticed problem persisted but not as bad. Hooked DRB up and drove again. Once engine reaches normal temp and under load I noticed the rail pressure dropped from 15000psi to 3000psi. Off accelerator pressure goes back to 5500psi. No codes are present. Filter has been changed and low fuel pressure is good. Was thinking FCA, but wasn't sure. Help please!!!!

 

This link maybe of some help

https://www.dieseltruckresource.com/...d.php?t=304076

 

Sorry that really doesn't help my problem. Did try the FCA, but it still acted up. It only seems to do it when the engine reaches 210 degrees. I don't understand. All wiring and connections are good.

 

My truck did the same thing a few months ago.
The electric part of the fan clutch was bad/open circuit. Replaced it and now rail pressure is good and the truck runs normal.