ML63 Charging Voltage suspect?

[Nawaz SouthSudan]

I bought an ML63 6.2V8 in November 2017. The starter "felt lazy" so took it up the motorway - 200miles later - no improvement. The charging voltage after 200 motorway miles was an indicated 12.4V on the dashbord.

So changed the battery for a new MB from dealer in March 2018. No improvement.

So changed the alternator - new MB from dealer in June 2018. Charging improved to 13.4V to 13.7V on the dashboard. When measured with a Fluke, it is over 14V.

2 things:

1) Starter still "dips speed" on cranking-turnover - even with a warm engine before ignition...

2) Very puzzling: when you "blip the throttle" - voltage goes down before increasing? How?

 

[alexanderfoti]

1) Possibly faulty starter?

2) There is a one way pulley on the alternator and active charging management by the engine ECU. This will remove/reduce charging under certain conditions (overrun = max charging, revving or full throttle = minimum charging).

 

[Nawaz SouthSudan]

1) Possibly faulty starter?

2) There is a one way pulley on the alternator and active charging management by the engine ECU. This will remove/reduce charging under certain conditions (overrun = max charging, revving or full throttle = minimum charging).

@alexanderfoti - Thank you. Now - is there a way to test the starter for a fault like worn brushes, partially overheated windings?

New generation mechanics - replace modules... not repair.

Point 2 is very silly of MB to do... - I have the "devil's chariot" - an X6 4.4 Twin turbo - with similar setup... causes no end of problems with the battery...

 

[alexanderfoti]

The one way pulley is there to save the life of the belt, as the alternator has a lot of inertia with rapid speed changes.
The active charging management is all in the quest for better fuel economy!

There may be, but I do not know how. This would be the domain of starter repair places , or motor rewinders. You could extrapolate based on the current draw, but I don't know what the right value would be.

Have you checked grounding straps aren't missing etc?

 

[Nawaz SouthSudan]

Will check the ground straps... and current draw.