ago in Mercedes by
My little one is having problems. Maybe you have ideas what it could be:

Cold start no problem, but warm start (engine shakes and organizes, sometimes it struggles and starts and then runs well, sometimes it goes out completely and you can try it again.

What has been exchanged so far (currently approx. 111000km)

- coolant temperature sensor as described above (current)

- About 2-3 years ago filter unit including gasoline filter & fuel pressure regulator (there was a similar problem before, but not the same)

- I also replaced the crankshaft pulse generator at that time

- Gasoline injection nozzles were also replaced not too long ago.

What I've tried so far:

When it is warm the key is on ignition for longer so that fuel is pumped. -> No improvement

Key 2-3x on ignition without starting -> as above

Have the pressure measured at the front. When the car runs approx. 4 bar, when it is warm, the pressure drops to approx. 2 bar (but I think that is still within the limits?)

Unfortunately I haven't measured it cold yet. What was striking was that there were bubbles in the gasoline during the bad warm start ... Now the question is, of course, where? Can't the fuel pressure regulator in the tank be over again, can it?

It is a R171 Bj 2008 with 184PS.

2 Answers

0 votes
ago by
Everything speaks very much for fuel pressure regulators.
0 votes
ago by
Although this has nothing to do with the engine start, it is a well-known phenomenon.

The fault with my SLK has also been there since last year. The mistake is quite common and comes with the age of the vehicle. The fault pattern is actually inconspicuous until you drive in wet weather. It can happen that the window suddenly starts up from the inside and there is little visibility because the air conditioning compressor is no longer properly controlled (better said, its electromechanical clutch).

The cause is apparently due to dried-out electrolytic capacitors in the SAM front. In order to repair / replace them, the entire unit has to be removed and cut open with suitable tools, the capacitors replaced and the whole thing tightly sealed again.

To start the engine:

I would look at the fuel pump in the rear, or rather the valves on the rail pipe. If a valve is no longer properly sealed there, the rail pipe pressure is not maintained after it has been switched off. As a result of the lower pressure in the rail pipe, the boiling point of the fuel drops and there are vapor bubbles. When the engine is cold, the vapor bubbles collapse again and the problem appears to be gone.
ago by
I also heard about the refrigerant compressor. Well, I haven't noticed it so far. I only have the very "cheap" version of the air conditioning control unit, so without a digital display etc. What I noticed, however, is that the idle speed fluctuates slightly when the air conditioning is running. But really only minimal.

But the start-up problems cause me more concern :)after that.

With the valves on the rail tube do you mean the injectors? If so, they are relatively new. Approx. 1 year. I just wonder what this pressure holding thing on the rail tube is for? Respectively. whether that can not cause problems (?)

Of course I still hope that the filter unit with the check valve is not broken again. That would be a certificate of poverty for "MB original quality".

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