I've replaced a lot of parts to fix that car (wires, plugs, injector, coil, EHA...), it's getting really better now but I'm still having a starting issue.

If I have to re-start the car less than 15 minutes after I turned it off, it will start right away.

On all other times (cold or hot...) when I start it, after 1 or 2 seconds of cranking it looks that it's starting for like 1 second and then die. If I re-crank just after that: it starts right away!
If I initially crank it for a longer time (like 3 to 4 seconds) it starts fine also.

Fuel pump check valve have been changed without success. Any ideas?
I've eared about mass plate position adjustment?

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From 300CE to SLK230K