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Old 09-14-2020, 01:53 PM
oldskewel oldskewel is offline
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Quote:
Originally Posted by jac View Post
Hi gents, thanks for the observations. I am learning from you all.

I saw the 13.4 when I first turned on the car and as it idled for a few seconds. That's all I had observed. But now that you guys informed me that 13.4 is on the low end, I have taken the time to observe it further.

So, my observations are:
  • Voltage: starts at 13.4 after about 3 seconds from cold start, and while in Park for at least first 30 seconds (not sure if it climbs or stays there if it stays in park for a while)
  • Voltage: 13.4 while reversing from park
  • Voltage: 13.6/13.7 while driving at around 20 miles per hour
  • Voltage: 13.7 while driving at higher speeds than 20 miles/hr

The alternator is a new Bosch 140 amp unit. Well, it is supposed to be new, at least according to FCP Euro. But I am not certain because the box is a retail Bosch box nicely sealed, but the unit has a Bosch sticker, but the plastic part says Valeo... I am reaching out to FCP Euro to check.

Thanks!
Wow, that's a shocker on the Bosch / Valeo hybrid you've got. Let us know what the answer is. Am sure it's OK, but still weird.

On the voltage, as was said earlier, it matters where you measure it. A voltmeter measuring at the B+ jump port in the engine bay will give you pretty close to exact alternator B+ voltage.

Measure anywhere other than that point, and voltage will be lower. I think I remember noticing the built-in high cluster internal test showing consistently up to half a volt lower than the true alternator voltage.

You'd get similar results if using one of those voltage gauges that plug into the 12V outlet.

The electronics like to have regulated voltage, and generally regulating voltage (for stability and control) means reducing it a little.

My guess is that things are fine with the new alternator, and that you have solved your problem. But it is a little concerning that the store did not confirm your old alternator as bad. Those tests are always a little suspect. It could be that you have an intermittent problem - diode conducting or not, for example - that somehow temporarily fixed itself during the removal, disassembly and reassembly.
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