Low Voltages from relatively new alternator

[jwakil]

I checked my voltages on my 81 930 and was surprised to find relatively low voltages and not sure if there is something wrong. Very occasionally I got a tach bounce which is why I checked in the first place but the car has been running fine and the battery obviously has maintained at least enough charge to start the car for some time. I do NOT get the alternator warning light coming on in the dash. Here are the voltages I measured at the battery:

at idle, 12.6 V
at idle, with lights on 12.0 - 12.1
at idle with AC on 12.2
at ~3000RPM with AC ~12.8-13.0
car off 11.9

My understanding from the PO is that the alternator is ~2yrs old, less than 5k miles put on. Could this be a voltage regulator issue or the alternator? It seems to have an MSD ignition box where normally you would see the black voltage regulator. Does the MSD system replace the voltage regulator or do I have the voltage regulator in the alternator itself?

Update #1.....
I found out I have an externally regulated alternator (Bosch Al9341X) and somewhat of a mismatched voltage regulator (911-603-206-13-M260 which is original to the car). I pulled out both, and took them to a reputable alternator shop. They tested both and said they worked fine together, and there wasn't anything wrong with either one. I reinstalled both, made sure the fan belt was properly tensioned, and still basically the same voltages as you see above. I also checked these voltages on the fuses in the engine bay, and they read basically the same. I also checked the ground strap from alternator to engine and it was fine. The only thing which I haven't really checked is the ground strap from trans to the body. But I would think that if there was something wrong with that ground strap, I would have trouble starting the car, but it never has issues with that.

Update #2
I had the battery checked out, other than being low on charge, they said it was Ok.
Also inspected the ground strap from the transmission to the body. I couldn't really see or feel any problems there.
Also, today I'm noticing the voltages slightly higher...but not high enough
at idle with AC ~12.5
at idle no AC ~13.3
3000 rpm with AC ~13.0

Update #3
Forgot to mention that there is an MSD RPM activated switch installed by the engine bay relay/fuse panel. I don't know what the switch is really for. I know that when I start the car, I have to rev it up a little before the alternator light goes off (then it stays off). The PO told me that was part of the normal routine. Could this have anything to do with the low voltage values?


I'm running out of options here....any more suggestions?

[howard freeman]

MSD,does not replace voltage regulator. Yours certainly has the later style alternator with regulator mounted on the back of the alternator. Try to find out what brand alternator was installed,the Bosch remans can be problematic. Use only new Valeo alternators. What type ( brand) meter are you using to check the voltages. You really should be seeing about 13.4 volts @ 3000 rpm. It could also be a bad ground strap that runs from the tail housing of the tranny to the body on the right side.
Howard

[Joe Bob]

Locally rebuilt alts are OK if the builder can get parts. It's the remans that come from the national chain stores that suck.

As to your numbers on the battery. The at rest voltage is low, try charging it with 110 v charger. I would have it tested. Sitting voltage should be 12.5v+.

Is your meter accurate?

[jwakil]

My meter is accurate. I initially checked using one of those you plug into the cigerette lighter and I didn't believe what I was seeing, so I checked using another digital volt meter directly at the battery and it confirmed the same numbers. I will pull out the alternator and look at the wires and have it tested. I wanted to paint the fan anyway so this will be a good chance for that too. I just hate not being able to drive the car though...

[HawgRyder]

First thing to check are the ground wires and connections...ALL of them!!
I always say...if you are not willing to lick the connection with your tongue (don't really do it!) then they are not clean enough.
The alt is grounded to the engine...the engine to the trans...and the trans to the frame up at the front by the shift coupler.
The battery ground should be nice and clean up front....and check the posts for corrosion too.
Good luck
Bob

[wwest]

Originally Posted by jwakil

I checked my voltages on my 81 930 and was surprised to find relatively low voltages and not sure if there is something wrong. Very occasionally I got a tach bounce which is why I checked in the first place but the car has been running fine and the battery obviously has maintained at least enough charge to start the car for some time. I do NOT get the alternator warning light coming on in the dash. Here are the voltages I measured at the battery:

at idle, 12.6 V
at idle, with lights on 12.0 - 12.1
at idle with AC on 12.2
at ~3000RPM with AC ~12.8-13.0
car off 11.9

My understanding from the PO is that the alternator is ~2yrs old, less than 5k miles put on. Could this be a voltage regulator issue or the alternator? It seems to have an MSD ignition box where normally you would see the black voltage regulator. Does the MSD system replace the voltage regulator or do I have the voltage regulator in the alternator itself?

Now check those same voltage, same "sequence", at the Fuse panel in the engine compartment.

Meantime check/tighten the F/R positive side "crosstie" at the starter motor solenoid terminal. Also make sure the engine is well grounded to the chassis.

[jwakil]

Originally Posted by wwest

Now check those same voltage, same "sequence", at the Fuse panel in the engine compartment.

Meantime check/tighten the F/R positive side "crosstie" at the starter motor solenoid terminal. Also make sure the engine is well grounded to the chassis.

Where/how would I check at the fuse panel?

[brads911sc]

Check your fan belt.

I found that I don't get the 1/4-1/2 inch of flex as per conventional wisdom unless all my shims are on the outside. all 5 of them. i have zero on the inner side. made a .50 volt different across all scenarios on mine. perhaps there is some variation in fan belts?

oh and you can get a brand new bosch AL 400 N for the SC for $275 on Amazon with a lifetime warranty and 2 years road side assistance. So don't waste your money on a reman one that likely will cost you more than a new one.

Originally Posted by jwakil

I checked my voltages on my 81 930 and was surprised to find relatively low voltages and not sure if there is something wrong. Very occasionally I got a tach bounce which is why I checked in the first place but the car has been running fine and the battery obviously has maintained at least enough charge to start the car for some time. I do NOT get the alternator warning light coming on in the dash. Here are the voltages I measured at the battery:

at idle, 12.6 V
at idle, with lights on 12.0 - 12.1
at idle with AC on 12.2
at ~3000RPM with AC ~12.8-13.0
car off 11.9

My understanding from the PO is that the alternator is ~2yrs old, less than 5k miles put on. Could this be a voltage regulator issue or the alternator? It seems to have an MSD ignition box where normally you would see the black voltage regulator. Does the MSD system replace the voltage regulator or do I have the voltage regulator in the alternator itself?

[jwakil]

Latest update......also updated the original posting with this same info....

I found out I have an externally regulated alternator (Bosch Al9341X) and somewhat of a mismatched voltage regulator (911-603-206-13-M260 which is original to the car). I pulled out both, and took them to a reputable alternator shop. They tested both and said they worked fine together, and there wasn't anything wrong with either one. I reinstalled both, made sure the fan belt was properly tensioned, and still basically the same voltages as you see above. I also checked these voltages on the fuses in the engine bay, and they read basically the same. I also checked the ground strap from alternator to engine and it was fine. The only thing which I haven't really checked is the ground strap from trans to the body. But I would think that if there was something wrong with that ground strap, I would have trouble starting the car, but it never has issues with that.

I'm running out of options here....any more suggestions?

[Joe Bob]

As I mentioned....battery.

[timmy2]

Originally Posted by Joe Bob

As I mentioned....battery.

+1 Get the battery load tested. If it's failing it will lower the voltage readings at the battery.

[jwakil]

Originally Posted by timmy2

+1 Get the battery load tested. If it's failing it will lower the voltage readings at the battery.

I did charge up the battery overnight, but then let it sit for a couple of days before the latest round of tests which gave me similar results. I haven't had it load tested. I guess that's next on the list.

[jwakil]

Ok guys, I'm getting desperate now..

I had the battery checked out, other than being low on charge, they said it was Ok.
Also inspected the ground strap from the transmission to the body. I couldn't really see or feel any problems there.
Also, today I'm noticing the voltages slightly higher...but not high enough. I really can't attribute these slightly higher numbers to anything real I've done since my last reading when I reinstalled the alternator and regulator and basically got the same readings as I had the first time.

at idle with AC ~12.5
at idle no AC ~13.3
3000 rpm with AC ~13.0

Running out of options....any more suggestions

[jwakil]

Forgot to mention that there is an MSD RPM switch installed by the engine bay relay/fuse panel. I know that when I start the car, I have to rev it up a little before the alternator light goes off (then stays off). The PO told me that was part of the normal starting routine. Could this have anything to do with the voltage values?