E36 Alternator D+ Voltage Issue

[sequoianorcal]

Trying to figure out some odd voltage readings on the alternator D+ (BLU) circuit.

My alternator was working. I had similar voltage readings with that installed, although closer to 2.0v in ACC before I replaced my battery with the bad cell under warranty. Removed it, got it tested (good, but a little low at 13.8), then accidentally broke the brushes in the voltage regulator while I had it off.

Pulled an alternator at the salvage yard to try as a replacement. It also works, but still have unexpected voltage readings with key off (between 0.02v and 0.04v) and ACC (1.15v-1.21v). But again, normal when engine is running without doing anything like increasing the rpms.

A while back I checked continuity (battery disconnected) between D+ and cluster and D+ and data link, which were both good.

Cluster battery bulb is good, and swapped for another, just in case, though didn't make a difference.

Just not sure what's causing this or what I've missed. I've read all the threads I can find, but nothing quite matches this.

Ideas for further testing or what the origin might be?

All the below readings were taken by backprobing other than the instrument cluster where it's not possible because of the connector style. Also couldn't find an x6091, so not sure if I have one (ETM says U.S. production).

Any help would be greatly appreciated.https://uploads.tapatalk-cdn.com/20220521/97bf9b4849bea5ffaf34412ae88ca0b7.jpg


https://uploads.tapatalk-cdn.com/20220521/84baf0bd989201872d84c2c81c7a8958.jpg

[Eric93se]

There may not be anything wrong, its just a little out of spec.

Have you tried fresh batteries in your meter? Older e36 alts regulate at 13.8 and newer ones regulate at 14.4

You could try a new regulator. You can also do a load test and see if the voltage stays high, turn on everything you can and see how it performs.

[sequoianorcal]

There may not be anything wrong, its just a little out of spec.

Have you tried fresh batteries in your meter? Older e36 alts regulate at 13.8 and newer ones regulate at 14.4

You could try a new regulator. You can also do a load test and see if the voltage stays high, turn on everything you can and see how it performs.Multimeter battery was replaced within the last month. Also got corresponding readings with a power probe 3.

What concerns me is the voltage on D+ in ACC (and very low voltage with no key at all). My understanding is that with the key on (engine off), the exciter wire circuit should show 0v and cluster battery light should be on. But other posts I've read with similar things have also had that circuit not function correctly with the engine running, so are having charging problems, which I don't appear to be.

My battery light comes on, because there's a large enough voltage difference between the two wires, but not what I'm expecting it to be (12v B+ and 0v D+).

I have been suspecting a wiring issue of some sort since I've had the same thing going on with two apparently functional alternators, but the readings I got aren't obviously pointing me to anything (at least with my current level of knowledge).

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[Eric93se]

The excitation voltage that comes from the bulb only comes on for a second, when the alternator starts to generate power there is no longer a potential difference across the bulb so it extinguishes. The bulb may be 'high' on both sides and that alone may be a couple tenths of a volt.

There have been members that had the excitor wire damaged.

[onesikM]

I have been chasing my tail just like you as well trying to determine why I’m not seeing charging levels above 13.8 most of the time too. Here’s what I’ve found, you will tend to see the lower voltages when the engine is temps increase as well as it will be at its lowest during the summer months since its temperature dependent from my understanding. Now as the weather begins to cool down my charging levels have bumped up closer to 14.2 when idling after a long time and the batteries are topped off. I’m using lithium cells currently that I made for car audio purposes paralleled in with the standard h6 battery and eventually I’m going to remove the agm and mount this lithium pack in the normal location but for now I got it strapped in the spare time/storage space.

One other very important topic I would like to raises attention on to since this relates to alternators and charging, guys stay as far away as you can from autozone alternators and others alike. They are going to sell you an overpriced Chinese made brand new alternator that is flooding the market right now and my recent experience with them as been horrific to say the least. But what they are selling everywhere right now is the silver pulley alternators that can be found at online stores labeled under differnt brands or retailers for example like tyc is one I can think of of the top of my head. I purchased one of these 140a chinesiums shipped to my door primer for 121$ this year. Don’t be too concerned if your on a budget and you need an alt go for it if you can get it for that low price that I mentioned. But what ever you do please don’t be fooled at autozone into overpaying for the “new” or “remanufactured” options they will try to offer you. Man I can go on about this for days lol. So I found out how bad these Chinese alternators are when I had a sudden urge to try and have a look inside the unit and my hopes was to tweak the voltage regulator to pump up the charging voltages a little to boost the sound system output and this turned into a nightmare to say the least. Ohhh I can see it now in the future all the alternator/starter rebuild shops are going to be cussing this garbage out when the same thing happened to me happens to them. When I went to remove the back cover of this alt I found that it was impossible to remove the 8mm nuts holding on the plastic cover, basically the studs they are on goes thru the rectifier diode bridge and little did I know they are made out of the worst possible material that when I went to undo the nuts the whole studs began to turn. This led to a broken alternator one that wouldn’t charge anymore…big sad. Went to autozone on a whim while I was trying to talk to the Amazon seller about the issue I had. My autozone was like ok it’s 270 for the rebuilt alt and 350 for the new. I’m just throwing numbers out there don’t quote me on that but they are in the ballpark. I asked to worker to bring both of them out to have a look. The dude brings out both boxes and I opened them up and chuckled and said to him hey kid can you tell me here which ones the new one and which ones the rebuilt one ? LOL both of them piles were brand new….i was disgusted the way they prey on peoples stupidity and over sell junk. Basically I ended up switching mine out with there’s and returning in and I had no shame in doing so because it was the same garbage and knowing how much I paid for mine I wasn’t about to pay 3x more. The Amazon seller later I found out just refunded my money and said throw away the defective unit. Nice guy his store is Oeg Parts. So if you are a diyer and like to tinker I suggest staying away from off brand alts, currently the red flag give away is the shinny silver pulley they are coming with.

Oh ya so then the new alternator I have I cautiously tried to again open the rear cover and guess what, the same dam thing!! Obviously this time I didn’t break this one and tried holding the stud to back off the nut but nothing I tried worked so I gave up. I went to the local junk yard and found myself a real bosch which is practically brand new so I’m super stoked and lesson learned. But the bosch x part numbered rebuilt units or don’t even bother with these fake units that will not let you do any repairs in the future. I’m currently about to test my alternator with the changes I made to the regulator and im expecting to see atleast .5 volt increase

Sorry for the long read Hope someone finds this useful :)


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