Okay I know this means I need a new voltage regulator, my Haynes manual says how to replace it, and I imagine I can get a new one at my local auto store. I haven't verified the voltage with a voltmeter yet, since mine's broken and I'm waiting for a new one to ship. But it reads 12.5V when the engine isn't running, and it goes a little beyond 16V at higher rpms, so I suspect it's accurate.

Problem is, the last owner already replaced the alternator. Sure enough, it was the only clean thing in the engine bay and its belt was new while I had to replace the other belts. That was 8,000 miles ago.

I remember reading somewhere on these forums about someone who replaced their alternator multiple times. Even if I could search for it, the search tool is being fussy. So can someone tell me what to check so I don't blow another voltage regulator?

 

That voltage is created when the engine is running and the alternator is the source of the voltage. Your problem must be in the alternator weather it be the voltage regulator or something in the alternator its going to be comming from that component.

And above all else get the right voltage before you go worrying about this too much. They have charging system testers at autozone that can tell you exactly what its putting out. Compare it to spec then worry about the voltage.

 

yea you can take your alternator over to auto zone to get it tested. although im almost sure that the regulator is internal on the s4 alternator so when he replaced it that should be a new alternator. i would make sure the regulator is hooked up. plug behind the alternator. a bad battery can be mistaken for a bad regulator. if your batttery is dead your alternator is working double time. check voltage after the car has been sitting for a while... i wouldnt always jump to conclusions, that may be why the alternator was replaced in the first place, although it may not be the problem... Good chance that it is the regualtor but i would also check the other stuff.

 

The regulator is internal in the FC and FD alts.

If you have a bad regulator, you have a bad alt

 

Yeah, but the Haynes manual says I can remove the alternator, open it up, desolder the old regulator, and solder in a new regulator. Can I not do this? Would an auto-store have the part, or do I have to go to the dealer? For that matter it says I need a 200W soldering iron to heat up some bearing or something before it can be removed, and I've only seen 30W soldering irons for sale. Is there another way?

The voltage has been reading normal for the last 8,000 miles since I got the car: ~12.5V w/ engine off, ~14V w/ engine on. It just now started reading 16V when I started my car today, unless I didn't notice it last time I drove. That's unlikely. Belt tension seems normal, about 1/2" of deflection.

What does the regulator plug look like? Where exactly is it? I see 4 plugs near the alternator on its side. EDIT: I found a plug that plugs into the back of the alternator. I assume that's what you mean. It's wiggling but I'm having trouble pulling it out. I'm gonna get my pliers, pull it, look at it, clean it maybe and plug it back it good.

Is there anything that could have caused this alternator and the last one to fail that I should check?

 

sure you can do that, usually easier just to replace the alt.

And there is only one plug on the alt and a positive post output terminal. Again the regulator is internal to the alt. To replace it, you would need to remove the alt.

And don't drive the car at 16 volts. The ECU and lights are designed for 15 volts maximum. Running them at 16 volts will burn them up and let the genie escape.

 

Trust me, you need a huge soldering iron to desolder the regulator. I held my 30W iron on it for ten minutes and it didn't make a mark. Just pay to get it rebuilt.

 

hahaha my soldering gun is 140w. that thing solders 2-4 ga. wire in seconds. it also melts the plasting sheathing. no good for electronics though. I agree, get a new alt. Regulator bad= bad alt. There could be other factors as to the 16v output beyond the regulator.

 

Uhg... I did NOT want to hear you say that this close to DGRR. I've been trying to figure out why my car is running over 15v for months . Of course... I suck at electronics, more of a mechanical guy. If replacing the alt doesn't solve your issue and you figure out something that DOES.... PLEASE let me know. I have replaced my alt 2x already and replaced the battery but the voltage is still over 15v. I have double checked this with a DMM at the battery to be sure and yes, the plug for the voltage regulator IS plugged into the back of the Alt and belt tension is A-OK.

 

The plug in the back of the alt seemed fine. I ran my car again for a minute. Same problem. The alt seemed really hot too after only a minute, dunno if that's normal.

Why might this alt have blown so fast? Cheap rebuilt alt maybe? What are the "other things" I should check first? I saw some charging system items listed in the Haynes manual that I will check when I get my voltmeter, but those don't seem related.

So it's pretty likely that I just need to replace the alternator? Where do I get a replacement? At an auto-store? Or do I bring/send my old alternator somewhere? Where? There's a mechanic within close walking distance.

Is it safe to drive short distances? Like 15 minutes each way to the auto-store? (assuming the typical heavy traffic around here; it's only 1-2 miles away).

 

So where I go for this one? Mechanic for rebuild? Auto store for new alt? Ship in alt for rebuild? I can replace the alt no problem but I dunno where to get a new one. And I want to minimize looking around so I don't bug my friend too much.

 

the shitty thing is now a days its gonna be all electronics. crazy amounts of wires bmw CAN management use like 9 different comps craziness.....Anyway i wouldnt test it you dont want to risk damaging anything the alternator is very easy to remove if oyu can get a ride and there is an autozone close by they have testing equipment that can check the output and the regulator, if thats the problem then thats the problem most alternators are warrantied.

 

Ha! In a similar situation I played the MAPP gas card. That's a card I'll think twice about playing next time.

 

ah ic. Yeah there's an autozone nearby. Unless i'm getting the name mixed up. So I can test it, find out its bad, and get a new one there or what? I dunno if I can get the warranty. I dunno if the last owner even got a warranty.

 

I got a reman alternator last year with a lifetime warranty. I just replaced it yesterday with another reman for free since that one was bad (bearing or something). Just spend the money and get something with a lifetime warranty, whether it be free or reman. They didn't even test it... I just brought it in and told them it was bad.

Putting out 13.2v with my lights/brakes on wasn't making me happy. If I could of tried it with the A/C on who knows what it would of read.