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[Solved] AMG wont start on first attempt when hot.


Topic starter

Mercedes-Benz ML 55 AMG 2001 w163 5,5l V8, no turbo, automatic, VIN: WDC1631741A297248, 242kkm. Fuel pump replaced a couple of years ago.

Picture of a typical ML 55 AMG:!Alv3RQPn1ylAqE8bjbgqS9nj_mgh

The relatively old AGM battery (10 y.o. VARTA) checked and found good: cold start amperage almost as new, voltage drop at startup not lower than 10,44 V (10,14 V when not fully charged).

When cold, the car usually cranks and starts at first attempt - even in extreme cold conditions.

However the car has some issues with hot starts. This problem has been on my to-do-list for years, but now I kind of solved the more important ones and am intending to fix this one:

when hot, the car often refuses to start at first attempt - it cranks for a fraction of a second, but then stops cranking and does not start. 
It is not a huge problem - rather an inconvinience, since the second, max the third attempt have always been successful. And this does not appear to be a battery problem.

The only error my scanner could find which might be of relevance is that the engine block temperature sensor sometimes delivers implausible data. This could however well be due to an aftermarket engine heater I installed and the ECM is unaware of.

So what are my options / how do I proceed to find the root cause and to get rid of this inconvinience? Many thanks in advance for your helpful hints.

2 Answers
Topic starter

Problem Solved.
Or better said two problems : one electrical, and one mechanical, both starter-related. Fixed the starter, and the hot starts are OK again.

nice for you.

Just luck. As my wife was starting the hot engine, and I was standing by the open hood, I heard some improper noises coming out of the shadow where the starter resided. This gave me direction for further searches and a reason to visit the starter repairs shop which confirmed my suspicion.

That`s what we have to know regarding the highely praised Benz reliability. 21 years of service - and the starters start somewhat malfunctioning. Shame on you, German engineers 😉


Try some fuel injector cleaners. 

"Try some fuel injector cleaners. "
Tried that already. Resulted in a smoother idling, but did not affect the hot startup issue.
"Good luck."
Thanks a lot!

Your fuel injectors are dripping and flood the engine. Find a mechanic to do pressure clean them or change the injectors.

"Your fuel injectors are dripping"
Or it may probably be the fuel pressure regulator valve being not tight? The latter being not easy to access on this vehicle... If yes, is there any easy trick to check which part - the injectors or the regulator - is at fault? Thanks a lot.