Your low pressure system is good but the high pressure system is to low. This is where things get complicated. you could have injectors failing and returning to much fuel, you can have a failed high pressure pump, or a failed relief valve on the common rail. Or a faulty sensor. The problem can be isolated but this is where tech tool and those specialized fittings come into play. Unfortunately most mechanics these days don't understand the system and would have you change parts until it runs or have you replace the whole system. If you have a dealer come out and check it ask questions. How do you know it's my injectors, relief valve, sensor, high pressure pumps, or common rail. A good mechanic will have no problem explaining how he found the problem. I personally like to explain the failure and how the system works and how I determined the problem. I think it' gives the customer confidence in making a decision.
