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Old 04-24-2013, 05:05 PM   #1
jbatman
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Question Random Voltage Drop...Pulling My Hair Out

OK... I've searched the forum and come across similar scenarios as mine however never exact. I've tried [most] of the suggested remedies including terminals, cabling, etc and have yet to find an answer to my problem. This has been ongoing for a month or so now and I'm almost to the point of taking it to the stealership. I'm hoping someone can help me out! Here's everything I can think of:

I changed my front brakes a month ago and when I put the car back down from the jack and started it I couldn't get it to start. I tried cranking effortlessly for 5-10 minutes until I could begin to hear the car really trying to turn over, and eventually turned over. Never had that issue before and noted that it was weird to happen after I had jacked it up and done a brake pad replacement.

From that point on I started seeing my red battery light come on intermittently. Sometimes it would come and go in less than a second and sometimes it would linger for a while. When I do see it come on, revving into high (4k+) rpms seems to make it go away. Sometimes after pushing it into high rpms it will stay away for 5-10 minutes and other times the light will come back on almost instantly once the rpms come back down to normal (1-2k).

I've also noticed that I have a better success rate of not seeing the red battery light if I have my AC on...not all the time but usually that can hold off the red battery light. With the AC on my avg voltage is usually 13.3v-13.6v (without the red battery light)

I haven't noticed it getting any more frequent or infrequent as time goes on either. Also, my car has yet to stall, die, or show any other cluster lights. I had my battery tested a week or so ago and it was at 70% charge. My alternator and idler pulley were replaced around 2 years ago as well.

I have a 20 mile drive to and from work (40 RT) every day. Now I get in the habit of putting my car into test mode when I start it before going to work and heading home. Here is the output from that:

*When the car starts I see it bounce between 13.8v-14.1v
*When I get the battery light driving my voltage is usually bouncing between 13.3v-14.2v
*If I get the battery light while stopped/idle my voltage reading is 12.5v. If I put the car in neutral and rev to 2k rpm while stopped I can typically bring the voltage up to 13.0v
*Sometimes at stop/idle it will sporadically fix itself and I'll watch the voltage reading go from 12.5v back to 14v almost instantly, usually if this happens (rare) the rpms will bounce around for a second or so between 400-600rpm and then the voltage will rise and it will fix itself.


I hope something within this clicks with someone because I've been racking my brain trying to find a correlation or pattern.

Thanks everyone!

Joe

Last edited by jbatman; 04-24-2013 at 05:16 PM. Reason: added more info
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Old 04-24-2013, 05:08 PM   #2
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Have you considered replacing the voltage regulator? See the maintenance link in my sig. GL!
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Old 04-24-2013, 05:10 PM   #3
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Random Voltage Drop...Pulling My Hair Out

Did you have a full charge and load test done on the battery? It sounds like you have a shorted cell possibly.


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Old 04-24-2013, 05:12 PM   #4
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Have you considered replacing the voltage regulator? See the maintenance link in my sig. GL!
I have considered that...I've been hesitant because I've come across so many possible solutions that prioritizing them is imperative or else I'll end up in the money pit trying to chase the answer.
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Old 04-24-2013, 05:14 PM   #5
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Did you have a full charge and load test done on the battery? It sounds like you have a shorted cell possibly.


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I've had a battery test done at autozone..not sure all that entails though. Man..I'd hug a stranger if it ended up being the battery.
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Old 04-24-2013, 05:15 PM   #6
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I have considered that...I've been hesitant because I've come across so many possible solutions that prioritizing them is imperative or else I'll end up in the money pit trying to chase the answer.
Battery, voltage regulator, and final stage resistor are of utmost priority. They are the very things you should turn your attention to first. They absolutely need to be replaced at this point of your car's life or you will experience failure.
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Old 07-24-2013, 12:44 PM   #7
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Update-

Still having this issue. I swung by the dealer and had them test the batt/alt with their handheld tool. They said everything read as it should. I didn't have them go any further considering they charge $160 just for a diagnostic of an issue. The alternator was replaced a couple of years ago as well as belts at that time. I took a couple videos today showing some of the symptoms in hopes something will click with someone. I don't have a ton of cash to throw at this so figuring out what it is without having to go through a ton of replacements in between would be a life saver.

Video #1 -


#1) Battery light has come on while on highway. I slow down and make a turn to get back on the highway going the other direction. You can see that as soon as I slow down, the voltage drops a little more, then picks back up during acceleration. This is without A/C, heater, radio.

Video #2 -


#2) I come to a stop at a light here. When I'm at a dead stop the voltage will creep down until it reaches around 12.4v, until acceleration.

Video #3 -


#3) If I am at a dead stop, and in the 12.x v's, I can throw it in neutral and bring up the RPM's which will also bring up the voltage. This was taken in the parking lot.

I have noticed that in the morning I usually see the light come on when I hit a certain area along my drive which leads me to believe it may be a build up or heat relation. I would say I see it hit normally at around the 10-15min mark upon initial start in the morning.

If the red light is on and I park and turn off the car, the red battery indicator will remain on if I turn the car back on directly afterwards and even after 10-15 of sitting. If I wait hours (say from lunch break to after work) the light will be gone.

I've yet to experience any sort of failure. BMW said my battery was low (65%) however.

I'm thinking maybe a tensioner or belt? I don't understand why I would be getting 13.4-13.8 volts with the light on while at high speed/high(er) rpm but when I come to a stop/idle the voltage drops back into the low 12's.

Thanks again for everyone's help.
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Old 07-24-2013, 12:58 PM   #8
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Random Voltage Drop...Pulling My Hair Out

You are still down to three things:

Battery: a "hand held thing" sounds like a chincy test. Battery must be charged fully and load tested to know for sure. If your starting sounds good and strong I would say it is probably ok.

Alternator: although you changed it recently it still may have gone bad.

Voltage regulator: known problem with e46 I would go there next.


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Old 07-24-2013, 12:59 PM   #9
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Most likely is alternator. I don't like your voltage bouncing around like that. Should be solidly close to 14v when engine is running.
Less likely is your battery if it is intermittently internally shorting out due to age or defect.

We can't tailor diagnoses or remedies based on your lack of money. I'd replace my alternator first.

EDIT: your vid convinces me. your voltage stinks. get a new alternator in there.

Who put in the last new alternator and what brand is it?

Last edited by Stinger9; 07-24-2013 at 01:11 PM.
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Old 07-24-2013, 01:49 PM   #10
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Sounds like alt to me too, OP, but it could just be the voltage regulator. Given your alt is only 2 years old, VR might do it for you. Also, so you know, if your battery is old and the alt is charging it a lot, from what I've heard, that will cause an alt to fail prematurely.

Safest bet is alt...assuming you really have checked all the connections and grounds.
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Old 07-24-2013, 02:23 PM   #11
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Originally Posted by Stinger9 View Post
Most likely is alternator. I don't like your voltage bouncing around like that. Should be solidly close to 14v when engine is running.
Less likely is your battery if it is intermittently internally shorting out due to age or defect.

We can't tailor diagnoses or remedies based on your lack of money. I'd replace my alternator first.

EDIT: your vid convinces me. your voltage stinks. get a new alternator in there.

Who put in the last new alternator and what brand is it?
An indie bmw shop put it in, it was a remanu bosch. I'd go back but I've since moved (to Dallas).
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Old 07-24-2013, 02:24 PM   #12
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Take a pair of jumper cables. Using only the negative cable do this.

Connect one side of the negative cable to the under hood NEGATIVE jumper spot on the passenger side strut tower.

Connect the other side of the negative cable to the engine/alternator on a good solid unpainted surface.

This is a supplemental engine to body ground, see what happens to your Voltage when you do this.

If you can figure out how to keep all of the his under the hood without falling off or causing issues you might be able to drive the car this way??
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Old 07-24-2013, 02:26 PM   #13
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Sounds like alt to me too, OP, but it could just be the voltage regulator. Given your alt is only 2 years old, VR might do it for you. Also, so you know, if your battery is old and the alt is charging it a lot, from what I've heard, that will cause an alt to fail prematurely.

Safest bet is alt...assuming you really have checked all the connections and grounds.
Yea seems I just need to bite the bullet and have a new alt put in. I'll try and get that done this wkend and report back. I would think it could be the VR but, to my understanding, being solid state that it would have failed outright and not been able to function, intermittently, for the last few months.
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Old 07-24-2013, 02:28 PM   #14
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Take a pair of jumper cables. Using only the negative cable do this.

Connect one side of the negative cable to the under hood NEGATIVE jumper spot on the passenger side strut tower.

Connect the other side of the negative cable to the engine/alternator on a good solid unpainted surface.

This is a supplemental engine to body ground, see what happens to your Voltage when you do this.

If you can figure out how to keep all of the his under the hood without falling off or causing issues you might be able to drive the car this way??
The car runs fine; never had a power failure. The voltage drops are random and for no apparent reason. When the voltage does drop and I get the red batt icon I usually just ignore it and it will return to normal anywhere from 2 - 20 minutes.
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Old 07-24-2013, 02:48 PM   #15
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You are still down to three things:

Battery: a "hand held thing" sounds like a chincy test. Battery must be charged fully and load tested to know for sure. If your starting sounds good and strong I would say it is probably ok.
That "handheld thing" is most likely a Midtronics tester that costs at the least $1K, and is the standard used by every dealership. It is a reliable tester as long as the inputs are correct.
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Old 07-24-2013, 02:51 PM   #16
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An indie bmw shop put it in, it was a remanu bosch. I'd go back but I've since moved (to Dallas).
Bosch is fine. What I put in my car when my original fail.
Depending upon who rebuilt it.

Could try to change voltage regulator if this is the cheap one. Two kinds and one is cost effective. Expensive one makes more sense to replace whole unit. Go for quality on alternator. Makes a difference here. Heard of plenty of lower tier ones fail.

If two years old, could not go back anyway. Standard guarantee is no longer than one year. That's why quality matters.
Indy has too much incentive to install cheap parts.

Last edited by Stinger9; 07-24-2013 at 02:53 PM.
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Old 07-24-2013, 02:52 PM   #17
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It is a reliable tester as long as the inputs are correct.
Do you know the theory here? Hand held cannot load test obviously. Curious how it could give accurate results.
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Old 07-24-2013, 03:03 PM   #18
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The car runs fine; never had a power failure. The voltage drops are random and for no apparent reason. When the voltage does drop and I get the red batt icon I usually just ignore it and it will return to normal anywhere from 2 - 20 minutes.
This is considered advice; to suspect the ground strap. I second checking this, but suggest you visually take a look at the actual ground strap under the car to make sure there is no rust or corrosion or loose connections there.
Tell us what you find under the engine.

Last edited by Stinger9; 08-21-2013 at 06:38 PM.
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Old 07-24-2013, 03:12 PM   #19
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This is considered advice; to suspect the ground strap. I second checking this, but suggest you visually take a look at the actual ground strap under the car to make sure there is no rust or corrosion or loose connections there.
Tell us what you find under the engine.
Will definitely check that first. I have to remove the plastic shield to see that don't I?
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Old 07-24-2013, 03:15 PM   #20
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Up on ramps, slide under car, and remove the shield.

For sure!
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