Junk HUCO VR or damaged alternator?

[Jay Laifman]

I have read various posts on this board about alternators and regulators going bad. This is on my '73 with Marchal alternator and VR.

The alternator was rebuilt within the last couple of years by AGS in Santa Barbara. I thought they seemed like old school knowledgable guys. Don't know if anyone has had bad experiences with them. But, they did tell me they could not rebuild my 912 generator, and could have just taken my money.

My car was working fine yesterday. Today, on the way to work, the charging light started going on and of all things the oil pressure gauge started reading really high. Because the alternator was recently rebuilt, and I never replaced the VR, I actually found a new VR near my office at Otto's of Venice. I installed it. Nothing changed. I drove home. I assumed I was running on battery or boiling them, one or the other.

I got home, pulled my multimeter and found that I was getting 12.02 V, with or without revving the engine. At least I wasn't boiling the batteries. I also turned on the lights and fan and it dropped the voltage to about 11.95, and did not move back up.

The oil pressure gauge continued to show very high pressure (like 120-140 psi), and it ran poorly, not wanting to idle. I'm assuming that is now because my Warm Up Regulator (on a CIS car) was having issues with the low power).

So, here's the question. Since I changed VR, it seems to be the alternator. But then shouldn't the VR caused the voltage to go back up the 12.02 V when I turned on the lights? Or, will AGS say the VR went bad and it damaged the alternator? Is there any way to know that?

Also, this VR is by HUCO, which I've seen some people say is junk. Could I have got a second bad VR? I'm assuming Otto's will never take it back, if that's what is still wrong.

[Jay Laifman]

Ok, maybe I should ask this. How do you bypass the VR on a '73 911 to see if it is the VR or the altnerator?

[timmy2]

There is no practical way to bypass a VR as it controls the applied voltage to the alternator to regulate its output. A known working VR is your best testing option.
Or take both to a shop for testing.
Check the positive starter connection as it is the direct feed to your battery. Also check your ground strap.

If you put a charger on the battery overnight, does the voltage build up? How old is the battery. My old battery died and took the VR out with it!

[Jay Laifman]

Thanks for the thoughts.

I have noted that a frequent comment is to take it to a shop. But aren't we on this board because we do much of the work ourselves? What is it about testing charging systems that is so hard or dangerous that someone at home can't do it?

I have seen that there is a way to disconnect the VR, and read the voltage off the alternator, by lightly increasing the RPM. If it goes above what it read before, it's the VR that's causing the problems. I've also seen that going to high can fry lots of stuff. But, I haven't seen detailed instructions on how to do it, if you were so willing to risk it.

And to add to my frustration, I just called a local shop and they said it would be $55 to test my alternator/VR. I hate paying for things I can spend the time to learn how to do, and do it myself.

[timmy2]

I guess you could build a test stand at home with a motor and belt drive to run the alternator with a speed controller to vary the RPM's as well as an adjustable dc voltage input to regulate the input to the alternator, and a load center with a battery to thoroughly and definitively test the alternator and regulator if you wanted to.....

As a professional industrial electrician knowing the cost to build it, I would rather spend the $55...

Do you have a link to the simple testing with the VR disconnected?

[Joe Bob]

High voltage or intermittent spikes is usually the VR. Low voltage is usually the alt. That said, fully charge the battery with an external source and test the output at idle and at 2500 rpms.

If you haven't already done so, call the rebuilder. I have used them for over 20 years and are the best I know. They should be the best source of help.

How old is the battery?

You may just have to pull the alt and take it back up to them. Buying a reman replacement is a crap shoot. Many fails out of the box.

[Jay Laifman]

Originally Posted by timmy2

... As a professional industrial electrician ...

Gee, if you are going to put it that way ...

I don't have any particular links to the instructions on bypassing the VR. I just remember seeing it as I was searching. But, it was for non-Porsches. So, I didn't want to even consider it unless I had a reputable Porsche person giving details.

[Jay Laifman]

Originally Posted by Joe Bob

I have used them for over 20 years and are the best I know.

Yeah, that's what I thought about them, and I'm not blaming them. I was just checking to see if my impression was shared by others. You never know.

[Jay Laifman]

Originally Posted by timmy2

Do you have a link to the simple testing with the VR disconnected?

I don't have a link. But I just got instructions from Zims on testing a generator on a 356 or 912 with the VR disconnected.

It says to disconnect D+ and DF. Attach DF to ground and D+ to a voltmeter. Start the car, keep the rpms low, slowly bring up the rpms. The voltage should jump to 35 V by 3,000 rpm - but not to do it for long because it can overheat the generator.

That's all I know. I don't know if there is a comparable test for an alternator. I also don't know if this is a good thing to do for generators.