Hi Guys, I have a puzzle that has me and my mechanic stumped, maybe someone out there can suggest a solution. My 2004 SLK 200 (80 000 Km) stutters when started from cold in the morning. This happens only in the morning, the rest of the day she is fine. The severity of the stutter is influenced by how hard she has worked the previous day and the morning temp.(The colder it is the worse the symptom) Some mornings it is so bad it appears as if she will die, upon recovery the motor runs perfectly for the rest of the day.

In order; the following has been tried, both actuators (inlet and outlet) removed cleaned re-programmed, Plugs replaced, igniters checked, Fuel injector rail with injectors swapped out, all vacuum pipes checked for leaks, fuel pressure checked at start, Tank return system checked, MAP and temp sensor swapped out. ECU software upgraded, intake manifold replaced. We also tried start-up with the airflow sensor disconnected, even in default mode the motor stutters.

The cam sprockets and chain were replaced on this motor at 70 000 km. No fault can be established in the installation or operation of the cam timing although we are unsure if the cams are returning to their startup position, maybe someone can enlighten me on exactly how the mechanism works? Alternatively I have begun to suspect a small water leak into a combustion chamber or an intake manifold, no water loss has however been detected from the cooling system.

There has never been a fault code recorded and the motor runs within all specified parameters on the MB diagnostic system.

Anyone solved a problem like this before, what suggestions?

 

Clean out the tank and replace all filters maybe...

 

This symptom did appear shortly after I (stupidly) added a fuel system cleaner to the tank. My initial suspicion was a leaking injector which was one of the first things that was tried after the plugs and igniters where checked out.

Fuel pressure comes up to 4 bar immediately the pump operates, before startup so it seems unlikely that it would be the filter in the tank.

Anyone had problems with the tank filter before.....what symptoms did it cause?

 

You aren't getting any codes? You may need to get it scanned with SDS. I have actually seen fuel additives ruin oxygen sensors. Hopefully that's not the issue for you.

 

I will give that a try. I did discuss that possibility with my mechanic but he said it was unlikely because the oxygen sensor is bypassed/ignored at startup, but I am desperate enough to try anything. He is willing to give anything a try as he has never seen this symptom on a MB before and he has been working on them for more than 12 years, 9 of them as the workshop foreman at a local MB dealership. He is accredited with MB and has their full diagnostic system. By the way what is SDS?