kula007

Hello.
I have a strange problem with my c63. With the car running, when I press the gas pedal, the voltage drops sharply. You can even see the lights dim.
When the car is turned off, the ignition is in position 2, when I press the gas pedal everything is ok, you can hear the throttles, the voltage does not drop.

link to the video below:

Someone had a similar problem?
Some suggestions what may cause the voltage drops?

Solo wing

My ML63 does the same thing. I think its normal as you blip the throttle the load increases on the crank pulley, the belt tension on the alternator changes causing the voltage drop. Someone please correct me if I am wrong.

ItalianJoe1

It only drops to 13v? That's not a problem.

Try it with the hood open. That locks out the alternator control, makes it charge full time all the time. See if it's the same. If so, probably normal. I've never bothered to troubleshoot any car that has voltage over 12.5ish when running, as that's normal.

kula007

I tried with the hood open, it's the same, I've also noticed that the voltage drops when I come off the gas pedal. You can see this in the video below. (I thought before that this was caused by pressing the gas pedal).

I also found that revs fluctuates when driving at the constant speed ie here at 110 km/h

Here you can see interior light dimming when car is idling.

I've started investigating this issue after last, more spirited drive when the ABS/ESP inoperative came on. It all went back to normal after switching the car off and back on, only CEL remained on.

Afte conecting car to xentry found 2 errors related with esp:
- C219700 one or more signals sent from control unit "Combustion engine" via the CAN bus is implausible
- C326600 Consequential fault

and two errors related with ME97 engine:
-0736 The position of the exhaust camshaft (cylinder bank 2) deviates from the specified value
-0073 Position sensor 1 for the accelerator pedal has a short circuit to positive

Thank you for your help

ItalianJoe1

I doubt you have a charging problem. I'd say probably a cam positioner issue, but I wouldn't be worried about the voltage.

hachiroku

sadly, many issues can cause this. if you've confirmed your battery is in good health and holding a 100% charge, and validated your alternator is correctly returning 13-14 volts from here on its a wild goose chase. one of my customers had an issue with a connector's pin arcing with a relay which was causing voltage to drop at random situations. it took him 6 months to figure out what the case was.

roadtalontsi

I swear some people just hunt and want to find problems with their cars. This is normal operation. This isn't a crappy 70s car that full fields the alternator all the time. It use algorithms to run the charging management system. Shuts the alternator off temporarily during acceleration. Helps with emissions and more power output. Typically you'll notice on decel it will full field and charge up a lot. Also notice the amperage. Understanding how volts and amps work together is important as well.

tmakt

@kula007 I have this same exact issue on a 2009 S63. Have you ever been able to identify the issue?

CaliBenzDriver

Voltage range from 14.9 to 12.6 is ok based on various factors.

How low does your voltage go?
13.0V or above: no problem!

How many Amps are involved ?
30A or less: no problem!

Voltage deeping during acceleration within limits is expected so long you don't see 12.3V or lower.

OP is dealing with a case of voltage gremlins soft-crashing ESP, making his tach shaky...

When the engine to chassis GND strap is oxidized the poor battery connection can hardly sustain part of the car load during decelerations.

🤞

swedepat

correct! =)