06SL500AMG

I'm looking at a 2009 S550 that starts then dies. That's unfortunately all I know about the issue. What're the possibilities even? Fuel pump, ignition switch, battery is what I've come up with so far. Has anyone ever had an issue like this?

MBCO

Your best approach is to scan the car with MB Xentry scanner. Any fault codes for all systems will be identified, current and stored. Your diagnostic work will be done. The work instructions to replace parts is there as well.
Throwing parts at these cars is not the best approach.

Senecat

"Why won't it start" is not a valid question anymore, much less with a Mercedes. Gone are the days of spark, fuel, air. The good news is, modern cars will usually tell you what's wrong with them, so long as you know how to talk to them.

Pull codes.

camplate

While I agree with what MBCO and Senecat say, in my case no codes were or are thrown. My car starts fine 95% of the time but if I add gasoline, either a fill up or just a few gallons, it won't start normally. Sometimes it will start and then die, other times crank but no start. The only way it will start is to have one foot on brake and other on gas, press gas down at least half way, sometimes more, and it will eventually start. It will run rough, need to feather the gas, but then will be fine until next fuel stop with a dozen engine stops and starts.
When my car would shut off after it started it was like the engine was still running. No indicators would change on display, I would need to push button to 'turn off' the car before I could try to start again.
The question for 06SL500AMG: how does it run when it does start, and how long?