First, sorry for the delay. I had a family emergency out of town and just got back.
I totally understand what you are saying as far as identifying which cylinders are causing issues. However, most times, the cylinders will misfire once or twice. Not enough to set the light. So even thought it may seem like it only happens every 2 or 3 hundred miles, it most likely is happening all the time, just unnoticeable.
Okay, this makes things a little tougher because a random misfire could be any of the cylinders. I did some research to see if there was anything listed under a Technical Service Bulletin and found nothing. As far as the fuel pressure, it is possible. Have you checked the fuel pressure regulator? Also, if there is no schrader valve on the rail, the easiest thing to do is to tap into where the fuel filter is located.
Other questions. Do you ever get a strong fuel smell? Has the fuel mileage dropped? Can your scanner tell you real time info on things such as the coolant temp sensor, short and long term fuel trims or anything that might help identify the fuel usage or what the computer thinks is happening?
Monday, October 19th, 2015 AT 5:40 PM