Purchased my 2004.5 3500 a year ago, it has 142,000 miles on the clock, it is stock accept for an Edge EZ. Ran flawlessly until last Sunday, I live in the Phoenix Arizona area so it was like 55 degrees out, the grid heater light came on so I waited to start the truck, it tried to start and failed, I tried again and it started, idled normally and ran great but the check engine light was on.  Turned it off at a friends house for little while (10 mins) it started right up, we went to a car show, when we came out it was even harder to start, it ran great all the way home, turned it off and it fired right up. I tried to start it the next day and it would not start at all, finally got it to start today and got the codes read. Your thoughts would be greatly appreciated! 

P0191 error code has to do with Rail Pressure sensor. I would verify all the wiring and connections. Then you might consider replacing the rail pressure sensor. You could test the rail pressure sensor by hooking up a live data tool and checking the rail pressure signal. 

Thanks MoparMan, I finally figured out that it was the pressure relief valve, I took the return line off at the CP3 and fuel came out, I temporarily blocked it off and it fired right up! Waiting on a new valve. 

Although your issue was the pressure relief valve (good information for me to validate some of my knowledge about the fuel system).  I wanted to share for you and others, that I have had "3" successive pressure sensor failures (over a period of 3.5 years), which the first one and third one were fairly straight forward; they failed low or open.  The symptom was the engine stopped running (even at highway speed with no forewarning) and there is no start function at all, dead.  I spent a lot of time troubleshooting and understanding the fuel feed steps/process/design/control to finally rule out the fuel feed i.e., starting from the gas tank all the way to the fuel injectors (including the computer inputs/outputs), and was down to two sucpect components  - the FCA and/or the Fuel Rail Sensor ( i wrote in detail about my troubleshooting which you may be able to look up., which explains how i ruled out the FCA).  The second failure was much more troubling to understand and diagnosis, but it was that the fuel pressure sensor had failed high or erratic, which caused the engine to surge, smoke, major loss of power, and not being consistent between these symptoms.  But again it was the fuel rail pressure sensor!  In fact, this started in 2015, followed by second failure (high dollar replacement part) in less than a year, followed by the third failure of a $25 bosch fuel rail pressure sensor off of eBay when it failed with approximately 10,000 miles and 1.5 years of operation.  The last failure (recently) did give me forewarning however by the engine becoming hard to start (i had to over crank the engine to get it to start and not run ruff) and it would run a little ruff and smoke a little too until it warmed up.  This hard to start or having to overcrank during starting actually was a very distinct and notable change that occurred and consistently continued for about 3-4 thousand miles before final failure (btw we took two long distant trips during this time).  Luckily,  ever since the second failure (the huge headache failure), I have been carrying a socket and ratchet with a spare fuel rail sensor in the truck and another spare sensor in the shop (ebay $25 ones).  This was smart since the third failure left my wife on side of road with horses in trailer, which I only had to drive out and meet her and just simply change out the sensor (since the signature symptom was that she lost power (again) at highway speed, and this was all I needed to know to immediately target the sensor).  When the sensor fails low or open, this is a significant reliability part issue with this diesel engine that leaves you on the side of the road (luckily I did not incur the significant costs of letting someone else "touch" my truck!).  Hope this helps; also try googling my previous post(s) of my troubleshooting details on the fuel system operation when I was learning about this for the first time (i.e., my first diesel engine truck).  I wanted to share this information since it can be perplexing when your in the middle of figuring out your problem.  Good luck and keep us posted.  

Edited August 28, 20186 yr by gudge
wanted to acknowledge originators failure part

gudge

 

Than you so much for taking the time to let me know what you have found, I will be buying one of the sensors to carry with me! Just recently my truck started leaking fuel from on top of the tank. Luckily it continued to run and the fuel leak wasn’t to severe as we were on a trip with our fifth wheel. I hate climbing around under my truck, so rather than drop the tank, I pulled the bed off. It was the plastic line where the return from the injection pump hooked up, I ended up installing an Airdog fuel pump and gutted the old fuel pump from the sending canister and used the fuel feed line at the tank for the return. It’s a never ending fight! I am thankful that the Lord gave me the ability to repair stuff! 

 

Thanks again for your information!