Alternator help/questions '89 Metro

[doviatt]

I've got a question for some of you technical guys. When I first got my metro last April I had to replace my alternator and battery. There was some discussion at the parts store at the time as to if it was a voltage regulator or just the alternator. This alternator has built in Voltage regular AFAIK. Replaced alternator and things were ok.

A couple of weeks ago my fairly new battery died on the way home from work. Got a warranted replacement on it and they told me my alternator was bad again. I ordered one but....I can't prove my old one is bad. I brought a battery charger and volt meter to work with me the last couple of weeks to check the status of things and keep it charged if needed. Things have been going well 'till today. I have been measuring about 14V on the alternator and about 12-13 on the battery.


This morning my radio turned off (sign of trouble) and when I get to work I measure 9.3 on my battery and 17V out of the alternator.

My questions:

1) Why does my batt/alt light not turn on? (It illuminates when starting- the light sequence test).

2) 9V on my new battery that can't be good right? I've got it on my charger at the moment here at work.

3) Sounds as if I'm having voltage regulator trouble. If it is part of my alternator does anyone know how I can separate this? If this is my second voltage regulator within a year is there some other electrical issue that might be taking out my regulator? Could a short or bad ground be something to look for?

4) My dash is crowded with instruments and guages (MPGuino, tach, vac). Why not add a couple more...I was going to get a voltage gauge to hook up to alternator. Should I get a second one to hook to my battery too?

Your help and advice is appreciated.

[Johnny Mullet]

Really sounds like a ground issue to me. First, double check the battery, starter and alternator terminals and make sure they are clean and tight. Next, check all the grounds. There is a large ground on the battery that goes to the trans and a smaller one to the chassis. Also there are 2 small ground wire connections on the back of the intake manifold on the passenger side.

[doviatt]

Johnny Mullet

Thanks! I was unaware of the ones behind the intake manifold. I will check them all (ground points you mentioned).

Appreciated!

[Old Mechanic]

Check for voltage drops at different points. Connect your volt meter's negative wire to the battery ground and check the engine, chassis, etc, to see if you have any voltage reading which should tell you where the grounds are weak. You should not see much if any voltage readings.

This is with the engine running.

If you read more than .25 volt you have probably found your problem.

regards
Mech

[doviatt]

Old Mechanic,

Thanks. That advice is pretty straight forward and makes perfect sense.. I'll give it a shot.

[Old Tele man]

...what's the voltage right at the battery terminals at idle? Should be about 12.6Vdc or higher? If not, it STILL could be a bad regulator (internal) or even bad diodes (also internal).

...if you 'slightly' rev the engine, does the voltage go "UP" to something above 12.6Vdc? If not check & clean all grounds (again). The alternator "output" voltage should go UP with engine speed somewhat, but not exceed about 14-14.5Vdc depending upon temperature.

[Johnny Mullet]

Minimum should be 13.6 VDC For alternator output. Should also read the same or very close at the battery.

[doviatt]

Ok, I put the battery on the charger right after I got home from driving it to work. Been a few hours now. Measurement results.

Remove charger. Measure at battery terminals.
Battery: before starting 12.4V
after starting 12.2V
No difference in measurement with rpm speed.

Alternator: 20.2V

I did measure a few points around engine and ground wire attach points with no significant voltage showing.

Looks like grounds are good? I will check again tomorrow just to be sure.

Looks like voltage regulator is toast?

I have a new alternator waiting at a local parts store but I can't pick it up till Saturday morning.

[some_other_dave]

What voltage are you measuring at your alternator? Between what and which?

The voltage at the B+ terminal (that's the big wire that feeds the power back into your battery; it may go to the starter first?) should be the same as the voltage across the battery terminals, to a large degree. An 8V difference either means that you are measuring something else, or that you have a huge amount of resistance in the charging circuit from the alternator through the battery and back to the alternator.

-soD

[doviatt]

I am measuring between the threaded stud on alternator that has large gauge wire attached and to near by strut mount point bolt (chassis). Sounds as if this stud is the B+ terminal you refer to. The only other connection is a multi pinned round press in connector with 2 or 3 wires in it.

I have measured this same point (stud) in the past when everything appeared to be working ok (battery charging by alternator) and have read 14V on that terminal. Last night before I put the charger on the battery that B+ terminal of alternator was measuring 24V.

I am afraid the huge amount of resistance in charging circuit is what I am seeing.
I don't know what to look for here though. Would a failed voltage regulator cause this condition? If it is internally regulated in the alternator this wouldn't make sense though.
How about this scenario. What if some one sold me an internally regulated alternator but mine is external? I could be this naive/stupid not to know how to tell the difference. Trust me.

If it does go through my starter first I guess I check starter connections? My starter works really well but this could be coincidental.