Using a buddies truck for a little bit but it has an issue. Truck is an 03 2wd manual with the small bully dog tuner with a little over 200k miles. I forget which model tuner it is. Truck starts and runs great but as soon as it approaches 175 degrees on the coolant temp it starts missing, running rough, and eventually dies. Does it while driving as well. The only code that shows up on occasion is one for the VP44 which is odd. Monitoring rail pressure while the truck warms up it slowly starts dropping then just quits. Unplugging the fca while running makes no change in how the truck runs or what is displayed for rail pressure. Im at a loss and have no idea where else to look. Help is greatly appreciated.

 

Check the defuel settings

 

Im assuming those settings are on the bully dog? The truck dies with and without the bully dog hooked up.

 

Unless you removed the tune and returned the engine to stock, I believe the settings will remain in the ECU. Try hooking the BD back up and follow the procedures to "return to stock settings" or at least look up the defuel settings that may be in place.

 

Remove all tuners and boxes first to verify its no an electrical glitch.

If it still does it, retorque or replace the cross over tubes in the head. Typical problem, the dropping rail pressure is a classic symptom.

 

I was thinking the same thing, Cross over tubes are loose going to the injectors causing a loss of rail pressure.

As was stated, the first thing to go would be the all boxes and tuners.