pillowshot

Hi all,

I'm wondering if a few of you could do me a favour. If you are idling and just tap your throttle pedal can you observe what your voltage does and let me know if it is similar to this:
https://youtu.be/HmQOUCeFq5s

Spoke to an alternator refurbishing business and they said computer controller alternators can sometimes do strange looking things. I'm trying to work out if this is normal behaviour or not.

Thanks!

pmercury

iTrader: (2)

not to me
weird never seen this before

pillowshot

​​​Hi @pmercury

So you're saying your voltage does not change at all when you give the gas pedal a quick tap?

Thanks

pmercury

iTrader: (2)

for me only up a bit or none
yes
but you never know, I can be wrong

JohnLane

Volts in my cluster always go up when I tap the throttle from idle. I'm in Arizona.... Land of forever full-fielded alternators with A/C never able to keep up with my black car!

OP I suspect a failing voltage regulator in your car.

pillowshot

Thanks for sharing your experience!

I have managed to get hold of a 48k mile S350 alternator (same part no.) And have thrown a new VR on it so for all intents and purposes should be in much better shape than my 120k mile one.

Getting this old one out is proving a pain.

Fried Chicken

Is that the sign of a failing voltage regular? Mine drops down at idle and goes back up under any load. I’m not sure what happens if the battery is critically low, say 11.2 volts.

pillowshot

As in when you're idling the voltage is lower? That is likely a VR.

My "issue" is if you tap the throttle quickly the voltage does a dip. From what I can gather this is normal (replacement alternator behaves the same).

I'm going to hook up a charger to my rear battery to see if that is the issue. Reads about 12.1v on the cluster with the car off.

Fried Chicken

This doesn’t seem like normal behavior to me. Mine does the opposite, it seems to not charge at idle but pops up at anything above idle. I’m not digging into the car without a solid diagnosis though. Is this a solid confirmation?

Regarding your car, that doesn’t seem like normal behavior to me, unless the revving of the engine causes it to draw a lot more power, which doesn’t make sense. I would tread carefully. Perhaps call mercedes and ask to speak to a tech.