I have a 2016 Ram with an eco diesel. Approximately one month ago, I attempted to start the truck and it took close to 45 seconds before it finally started. The check engine light came on and stayed on. Drove to Auto Zone and plugged in their reader and it came back with P0191, Fuel Rail pressure sensor etc. This continued for a few days and took it to my mechanic who has always been excellent. He told me it was a three step process and he would only do 1 at a time to see if the situation is resolved. First, the fuel filter was changed, didn't work. Secondly, the fuel rail pressure sensor was replaced, same problem. Thirdly, the high pressure fuel pump was replaced with no improvement. From the start the issue was sporadic as was the check engine light. It would be fine for a few days and then boom, it would start again. I also have to add, that once it started, I would have no more issues that day. It would always be a day or more later that it would reappear. Does anyone have any ideas or a similar problem that they were able to track down and repair?