Alternator / charging problem - Mercedes-Benz Forum
 
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#1 (permalink) Old 09-25-2009, 10:31 AM
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Alternator / charging problem

I had a couple of 'red battery warning messages and noticed that the car seemed sliggish on cranking. On checking the battery voltage was low - 11.8V engine running. Battery was replaced about 1 month ago.After much investigation discovered that the alternator does not 'kick in' until I rev the engine to approx. 3000rpm - it then charges away happly for the rest of the journey (at around 14.5V) even on tickover. Has anyone seen this problem before?
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#2 (permalink) Old 09-25-2009, 10:34 AM
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My cabriolet did the same thing . . .

No dummy light either.

Red, *<(:{)-
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#3 (permalink) Old 09-25-2009, 10:45 AM
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Quote:
Originally Posted by Red, View Post
My cabriolet did the same thing . . .

No dummy light either.

Red, *<(:{)-


Have you found out what the problem was??
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#4 (permalink) Old 09-25-2009, 11:02 AM
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Hey, Jetstream.

Are you a DIY type? If so disconnect the battery, pull the alternator, remove the regulator and check the rectifier bridge, windings and commutators. If that's all good then replace the regulator. If not then buy a rebuilt alternator and install it (the rebuilt will come with a regulator).

If you're not very well DIY inclined you could just buy the rebuilt alternator and do the R&R, that's pretty simple (just be sure to disconnect the battery first!).

If you really are not a DIY type at all, take it to a good indy and tell them what it's doing, let them run some diagnostics and they'll likely replace the alternator. Ultimately that's cheaper than having them check parts of it (as outlined above) because they would charge you for that time as well.

Since it changes with engine RPM, that pretty much changes the focus to the alternator/regulator, which is a good thing. At least you don't have to chase wiring.

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#5 (permalink) Old 09-25-2009, 11:32 AM
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Thanks gregs210. I was thinking (hoping) it's only the VR and yes I try and and do as much as possible myself. I understand that the VR clips onto the back of the Alternator and I was going to try and get to it from inderneath the car - leaving the alternator in situ if I could. Do you (or anyone else) know if this is possible?
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#6 (permalink) Old 10-01-2009, 01:44 AM
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Just to let everyone know - its NOT possible to get to the alternator from underneath the car.
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#7 (permalink) Old 10-15-2009, 12:01 PM
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An interesting footnote to this.

Whilst I was underneath the car trying to access the alternator I noticed a small amount of oil on the bottom cover / floor pan in the area of the alternator. I have now found that the jubilee clip which connects the charge air pipe to the tubocharger had snapped and whilst the pipe was in place it obviously wasn't sealed. There was some 'oil' directly under and behind the turbocharger which had obviously come out of the charge air pipe. I note that the crank case vent pipe is connected into the charge air pipe and this was the source of the oil mist which was building up and dripping down from the bottom of the charge air pipe. I cleaned up as best I could and replaced the broken jubilee clip. Car is running a treat and best of all the Alternator problem seems to have gone away - and I didn't touch the alternator at all. Now it's either a coincidence and the problem will return or the oil mist / drip was affecting the alternator in some way - the alternator being positioned just below the Turbocharger. Has anyone else ever come across oil contamination of an alternator?

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#8 (permalink) Old 10-16-2009, 02:35 PM
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WARNING!!!

If you do put in a rebuilt or new alternator make sure of the following:
The battery must have a charge in it of at least 12.8 volts.
If the charge is lower than that, take the battery to an auto parts store and they should deep charge it for free.
You should never install a new alternator in a system with a low charge battery. You could fry the bridge and then you are back to square one!
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#9 (permalink) Old 10-17-2009, 09:54 AM
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I have been having a "charging" issue in my 04 w220 and was wondering if yours did the same thing? I was thinking of having the alternator pulled and replaced.. my indy sucks (they always say - we dont know, weve never seen, etc); dealer seems to be 10x better.
Any idea on how hard to pull alt and replace myself? Im not much dyi but have friends..
is there a repair manual that I can buy like I have for all my motorcycles?

if the alternator doesn't kick in til 3k rpm, that would explain my issues.

I thought I had a bad battery as when I replaced the rear main battery my lights dimming upon a cold start went away... for a month or so.. now when I start up the car somewhat hums, etc and the lights in the cabin and everywhere in the car somewhat surge - if the car is not charging until 3k that would make sense?

Any suggestions or help is appreciated. Thanks in advance..
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#10 (permalink) Old 10-21-2009, 07:36 AM
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Quote:
Originally Posted by mvmiller View Post
If you do put in a rebuilt or new alternator make sure of the following:
The battery must have a charge in it of at least 12.8 volts.
If the charge is lower than that, take the battery to an auto parts store and they should deep charge it for free.
You should never install a new alternator in a system with a low charge battery. You could fry the bridge and then you are back to square one!
I have a 2002 S430 and alternator did go out, it is easy to remove it from the top. The trick is removing the fan from the radiator, JUST THE FAN. IIf i remembered it was 4-6 tork bolts.
BUT Before you do that call your dealer, when I bought my car in it was on a recall list and it was a mandatory replacement, so I did all the work for nothing.
Hope this helps
W
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