86 charging? or not?

[opie]

Took my Pcar for a drive today, got about 100 miles from home and the headlights go out and radio stars flashing on and off, then the car develops a miss. Pull over let it idle for a few minutes the miss goes away, take off and head for home. Ten miles away starts all over, the miss gets so bad I pull into a rest area just in time for it to die. About 6 hours later and a borrowed trailer I get it home and charge the battery, cranks up, put the volt meter on the battery and seams to be charging at first, 13.8 volts then the voltage starts fluctuating between 12.3 and 13.1 and keeps dropping. Does this sound like the alternator? just replaced it about 300 miles ago with a rebuilt unit? Will low voltage cause a miss?

[opie]

One more thing, batt. light never came, on but is functioning when cranking car.

[RedCoupe]

Yes, low voltage can cause a Motronic engine to miss or die. I had a bad cell in a battery and mine ran poorly and would sometimes just die at idle. New battery fixed everything. In your case, I think it could be either bad alternator wiring or connectors, a bad ground or bad ground wire, or a problem with the new alternator or its internal regulator.

[Walt Fricke]

I suspect the VR. Our '84 had a brand new VR fail in less than a month. The next one worked fine. It can be separately replaced, and you can do it yourself easily enough.

[opie]

Does anyone know what voltage at the battery should be when car is running? Mine is at 12.3 with no accessories on, turn the headlights on and it drops to 11.7

[86 911 Targa]

Originally Posted by opie

Does anyone know what voltage at the battery should be when car is running? Mine is at 12.3 with no accessories on, turn the headlights on and it drops to 11.7

13.5V @ 1500 rpm without accessories.

1. Check your V-belt (tightness).
2. Voltage regulator output.
3. Faulty alternator.

Good luck,

Gerry

[82 SC]

What is the top range of charging? I have a 82 911 Sc. Starts off cold with around 13.5 volts in the morning but when driving home with it is hotter it runs 14.5 volts. Hit 14.8 yesterday for a min.
Bad regulator? I know what happens when over charging a regular battery. Did that in my old Yanmar tractor and BOOOM! when the battery. luckily the battery was in the nose of the tractor and I did not get hurt.
later,

[GH85Carrera]

Shorty after I bought my 911 I went through similar issues. I finally sent my gauge in and had it modified. I updated my oil temp gauge to have numbers as well. It is nice to KNOW what is going on at any time and not rely on that tiny dim bulb.

[RedCoupe]

Originally Posted by 82 SC

What is the top range of charging? I have a 82 911 Sc. Starts off cold with around 13.5 volts in the morning but when driving home with it is hotter it runs 14.5 volts. Hit 14.8 yesterday for a min.
Bad regulator? I know what happens when over charging a regular battery. Did that in my old Yanmar tractor and BOOOM! when the battery. luckily the battery was in the nose of the tractor and I did not get hurt.
later,

A fully charged battery should read lower voltage at higher temperatures not higher than when it's cold. If you research it you should be able to find a chart showing this. 14.8 volts when warm is too high IMO. I had a too high reading in my Dodge pickup and it wound up being a connection not tight enough. You might double check all your battery connections and the grounds.

[82 SC]

Thanks Red, will check the connections. I have a little plug in volt meter in my cig lighter hole that I am checking the voltage as I drive around.

[whiz05403]

I had similar issues. I ended up pulling the ALT and having my shop re-do the ALT for a second time. Turns out the ALT was just fine.

I ended up doing a bunch of work when the real problem was a loose connection at the starter. Tightened it up and all problems went away.

Moral of the story: jack up car and check/clean all connections.

[82 SC]

Also some thing to consider is how is the meter you are measuring the voltage with?
Case in point, on a hot day the interior of the car is very hot. I have a little cheap cig lighter meter that i leave in the socket to see how my voltage is. On that very hot day before starting the car the meter read 13.3 volts not charging and when I started it it popped quickly to around 14.5 volts. Going down the road with higher RPM's I was getting around 15volts! Ughhh i thought. But when I was getting closer to my destination and my cabin heat was cooling off the voltage was dropping to around 14.7 volts.
Today was a cool morning around 60 degs and when I turned the key to see what the voltage was before starting the gauge read 11.7 volts. Hmmmm. Started the motor and was in the 13.2 volt range and drive down the road hit around 13.5 or so. Next step is to really check my cheapo volt meter against a real meter.
I work in a calibrations lab so it is also a good idea to know you have a good measuring device that is in spec when working on things. In my case i believe my charging is fine its the crappy meter that is giving me crazy readings..... Go ahead and get that better meter vs the cheap dollar store model. If I know my cheapo meter is reading bad I can at least use it to see if I am charging or not but know it is not for accuracy.

[Algernon]

Those 'crappy' meters that plug into the cig. lighter socket are not too bad - but the socket is over-size, and can make poor contact. Mine tends to read low until I jiggle it in the socket!

[DRACO A5OG]

^^^ buy a FLAPS standard replacement socket, cut the connector end off about 1/2" and slip into the existing socket then you charger and meter will stay snug. Down side lighter will not fit unless you remove the sleeve.

Dr. Bulczynski 3.2 Cigarette Lighter MOD $5.99

[pavegeno]

I plugged this (Amazon.com: INNOVA 3721 Battery and Charging System Monitor: Automotive) into a perm wired port under my dash and it has worked great for years. Highest I have seen after not driving for a while is about 14.2 volts and it quickly drops to about 13.2 after a few minutes of driving. Only see below 13v when the a/c is cranked, stereo cranking, and headlights on. a/c is a Griffith's with two additional condenser cooler fans in the LR wheel well so quite a bit of draw.

[pavegeno]

[Tremelune]

The voltage at your alternator might not be the voltage at your battery which won't be the voltage in your cigarette lighter.

How is the alternator/regulator wired? Direct to the battery over a thick cable? Ideally you would want 13.8-14.2 volts at the battery. This usually only occurs over 2,000 RPM in cars of this vintage.

Edit: Seems it goes from the alternator to the starter to the battery.

[82 SC]

Another cool day yesterday driving and voltages looked normal with the crappy plug in meter. If I can get a second I will check into it further. I just don't want over charging. I know what that does!
Boom with a regular battery.