It is possible that the fuel you are using does not have a high enough Cetane Number, which will affect the combustibility of the fuel. You can research on the internet many problems that people are having today dealing with the new engines and the ULSD fuels, such as sooting isssues of EGR Valves. This is caused in my opinion by low cetane fuels. The new ULSD fuels do not burn as hot as in past fuels and the EPA has mandated more restictive polution controls on vehicles. People who have and do use our additives have had no problems with there EGR's and the problem is widespread. In fact YouTube has a video showing how to disconect the EGR valve, and people are doing it even though it voids the warrranty of the engine. OEM manufacturers would like to see a 50 cetane level but american ASTM specs only spec a 40 Cetane. Over 50% of europeans drive a diesel vehicle, and there spec for Cetane is 50 and going to 55 in 2012. What do they know that we don't? I do know for a fact that when you increase the Cetane Number you reduce NOX gases and particulate matter which means less polution because your fuel burns cleaner.
That's not it. It has to do with the electric fuel pump in the tank not turning on for some reason when using the tip start function.