virgisr

My car has got 642 engine CDI, 2007, gerabos 7g tronic 722.9

When the car is moving, and i want to speed up, i start accelerating and it does not downshift properly, i have to kick it harder, a couple of times, then it downshifts.
Also, on cold start it cranks the engine for too long before the engine starts up. The fuel pressure builds up i guess. The fuel system does not maintain the residual pressure. Not sure where that prassure is failing to be maintained.
I tried to switch ignition on and leave it for 30 seconds, the pump at the tank prebuilds the pressure in that time. Then the cold start is ok, no long cranking before it starts up.

I have read some old thread in this forum, that problem with the downshift and long cranking are related. Possibly cause of the fuel pressure is not maintained properly?

Any advises are appreciated.

kajtek1

Replace the filters and get a gauge who can read rail pressure.
Than we can go from there.
Diesel's do drop gears like crazy similar to gasers.
Even at 2000 rpm diesel pulls like train.

virgisr

I did replace the fuel filter recently, thinking that could be causing my problem, but no change.
You are talking about high fuel pressure line check?

I was testing the low fuel line pressure some time ago when this issue appeared with my car. The pressure was building up to 4.5 bar on idle. When switched off it droped, but quickly. I was not sure if that quick drop is normal or not? Should not it maintain the pressure in the line?

Thanks for your reply

decorily

Perhaps you have an issue with your gearbox.
When you say that it won't downshift do you mean that the kickdown feature doesn't function?
Did you try a gearbox reset?

virgisr

i was going through that with independent mercedes garage, they performed the adaptation of the gearbox and said it functions very well, within all specs. So have to exclude this as well, i guess...