I have a 2006 r350 with approx 80,000 mi. Last November had the balance shaft repair done at the local dealership. We took a 2000 mile round trip Christmas visit to grandmas house and on the way home first experienced the start issue. After a day and a half on the interstate, we stopped for gas and lunch. After filling up with gas we stopped to have lunch. After the car sat for 30 mins. While we ate it wouldn't start. It would crank, fire and then die. After several attempts to start and about an hour on the phone with customer care, tow company and rental car agent, it fired and ran. We drove the rest of the way home with no problems. Since then we have had many no start issues where the car will fire and die immediately or just crank and no start. The car has been back to the dealership many times and the following parts have been replaced. Fuel pump, fuel pump relay, and crank position sensor. Still having the starting issues. The problem seems to occur more often after filling with fuel. On the last occurrence, the car would crank and not fire. I opened the gas cap and opened the steel flapper and there was a release of pressure. I couldn't tell if it was positive or negative pressure but there was a definite equalization. After that the car cranked twice more without firing and then started, however it was a rough low idle start. I had the vehicle at the dealership this morning for a short test and no codes were stored. The tech also did a fuel tank leak test and the car passed with an actual pressure loss of 4.1 hPa. I went back through old records and the charcoal filter canister was replaced in 09 when the car had 40000 miles on the clock. Does anyone out there have any ideas what may be causing my problems? Fuel system or balance shaft (cam timing) issue? Please help.