Technical Electric power loss

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Technical Electric power loss

Apr 30, 2019
I've been getting more loss of engine power when i use electricity.

Things like using window switch and hydraulic servo steering are consistent in slowing down my engine. Almost stalling when parking.

I have a Mercedes battery 660a 60ah, I've been looking after bad ground but the numbers on my multimeter is the same. (Gotta get a friend to see if I've done it correctly).

Any solutions?
Link for a video of the problem


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I think you have to rebuild your alternator. The collectors get damaged, especially one of them, due to dust. Small specs of dust get to it, cought between the brush and collector and act just like a grinder, wearing down the collector. It affects just one of them, the outside one, because dust is blown inside and sticks to that one, due to the cap. Here's a picture how it looked at my Punto Mk2 and it was also covered in a layer of dust, which I presume affected normal contact between brush and collector, causing output voltage problems. The multimeter read 14.2 V, but the battery was flat (without having abnormal consumers) and I had the exact problem you present, dropdown of engine power while using electricity. I didn't have an oscilloscope to measure the alternator output voltage, but I thought if I had one, it would read a bit different than the multimeter. Or if the voltage would be the same, the amperage surley couldn't be in good range. At the time (before winter started) I just cleaned the collectors, did not replaced it yet. I've bought one and will replace it. After the cleaning, there is no dropdown in engine power when I use electricity and the battery charges good now.


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Thanks dude!
I remember seeing my friend changing those parts on his costumers cars instead of changing the whole generator/alternator.

My car is older than me, so i bet it also have that slight damage.
if your engine idle rpm drops hard when putting a load on it then your idle control is reacting slowly or not at all. You mentioned it's both electrical and mechanical loads (like hydraulic servo), so i don't think it's anything wrong with battery or alternator, just the idle control.
Idle rpm is controlled by idle motor. It's a motorised valve in the throttle body, round black thing sticking out of throttle body held by 2 torx screws and has a 4-wire connector going to it. You can unplug the connector and test if the car behaves differently. That will tell you if the idle motor is completely non-functional (if there is no change in behavior) or just too slow (if it gets worse when unplugged).
Possible problems are burnt out idle motor, bad contacts in its connector that just require cleaning, a broken wire somewhere or a blocked (gunked up) air passage. To inspect that you need to remove the idle motor and look in the hole if it's blocked.

Note that small oscillation of idle rpm when turning on a powerful load is normal, but not so much that your car nearly stalls, and the rpm should recover to normal in short time.