Only 12.3 volts at battery and alternator

[baller760]

Not only do I have a vacuum leak somewhere, as I am only getting 8.5-9lbs at idle, but I also have a problem with the voltage. I'm assuming some wiring is bad somewhere but the scanmaster is reading in the high 11.0s in volts. Please help me, I already replaced the battery and had the alternator tested. Btw, my alternator says 108 amps and is AC Delco.

 

[441120]

Check the volt bulb in the dash, does it come on with the key on engine off?

 

[441120]

Oh yeah, wrong alt. but should still work.

 

[baller760]

Yes the volt light does come on. I played with the connections and a volt meter for a little to try to figure things out. I unplugged the grounds that go to the chassis from the negative battery cable to the little screw into the chassis. Still had the underhood bulb on but I figure that's because the black cable was still grounded to the block. Then I unplugged all of the alternator connections. Here's the really weird part. I went from the positive from the battery that connects to the alternator, to the positive connection on the back of the alternator (part you screw + from battery to) and I got 12.6 volts. Shouldn't I get nothing or close to nothing? It was acting like a ground which I thought was weird going from + to +.

 

[441120]

You just did a voltage drop test and found your problem
That wire is open, disconnect it from the alt and check the wire again, should be 0v. That might be a fusible link that burned.

 

[baller760]

Well it was disconnected when I checked it. The positive cable from the battery that connects to the alternator was disconnected. I put one end of the voltmeter on that cable as it was disconnected and the other end on the back of the alternator where I disconnected the + from the battery and I got 12.55 volts! That's what I am not understanding. Two positives and I'm getting as many volts as I get from checking the battery regularly!

 

[83ttypecooled]

Hi,
Was the car running when you did this test? I have never checked an alternator this way. I do know that all 3 wires should be hot, the wire from the the idiot light should light a test light dimly,due to the resistance of the lamp itself.If all else checks out, then you have an alternator failure.

 

[baller760]

Well with the motor running the voltage drops to 12.3 volts on the battery and the alternator. I also already took the alternator off and got it tested and it passed with flying colors 5 times in a row. Even got a new battery yesterday.

 

[TurboDave]

Well it was disconnected when I checked it. The positive cable from the battery that connects to the alternator was disconnected. I put one end of the voltmeter on that cable as it was disconnected and the other end on the back of the alternator where I disconnected the + from the battery and I got 12.55 volts! That's what I am not understanding. Two positives and I'm getting as many volts as I get from checking the battery regularly!

If it were disconnected when you made that test, then of course it's going to read 12+ volts. You basically opened the wire when disconnecting it. If the wire is connected to the battery and the alternator you should read very little to no voltage drop from batt. to alt.
Many alternator "tests" run by parts houses are usually suspect and rarely find a "bad" one. I wouldn't trust their tests. And it's also not unusuall to get bad ones from them right out of the box.

 

[GNVenom]

Be sure all the connections are secure. Then check for voltage between the alternator stud and the battery positive. Should be zero, maybe 1/10th of a volt. Any more than that, you have a bad battery positive cable.

I have seen a few failures of the cable because of acid "leeching" into the crimped connection of the battery positive lug - where the alternator, starter and ECM MEM wires are joined. The acid leaches thru the terminal and attacks the soldered connection, causing high resistance. If there is any significant voltage drop in any of the three connections, you found the problem.

Same goes for the negative cable. Always check for voltage drop with the engine running as it is consuming power and any drop will show up then. The age of our cars seems to make problems like these show up more and more.

John

 

[Blazer406]

One quick way w/o a meter to check to see if the alternator is charging..... is to (while the engine is running) place the tip of a screwdriver.... or anything metal..... on the center of the back of the alternator.....where the alternator bearing cap thingy is...... you can usually see it pressed in the case of the alternator.... you just get it close and touch this while the engine is running........ if it sucks your metal object (screwdriver tip) to it like it was magnitized.... then it is charging. This indicates the alternator field is energized and current is flowing....

I am not sure this will help you .... but might help someone in a pinch... to determine if the alternator is charging or not.....

 

[baller760]

Oh yeah, wrong alt. but should still work.

Well if the amps are too low on the alternator could that affect my voltage? What is the recommended amps on the alternator? Mine says 108 on the back. Also, I checked the positive and negative cables and the + is .02 volts and the negative is 0.00 volts. So, they are in good shape I would assume. When I have the car on I am still only getting 12.3 volts to the battery and alternator. When I took the car for a drive the scanmaster dropped voltage from 11.8 (12.3 with voltmeter check) to as low as 11.2. And the droppage usually happens when I give it gas or floor it. Now, I thought the volts would go up when you floor it because the alternator pulley is spinning faster creating more electricity? maybe I'm wrong. Please help.

I also have a post in the turbo section about a vacuum leak if anyone wants to chime in.

 

[baller760]

Just discovered that my volt light does not come on when I turn the key. Only the fasten seat belt and brake light. Also, the check engine light has never came on when I turn the key since I've owned the car. I use the scanmaster to check for codes.

 

[441120]

Well if the amps are too low on the alternator could that affect my voltage? What is the recommended amps on the alternator? Mine says 108 on the back. Also, I checked the positive and negative cables and the + is .02 volts and the negative is 0.00 volts. So, they are in good shape I would assume. When I have the car on I am still only getting 12.3 volts to the battery and alternator. When I took the car for a drive the scanmaster dropped voltage from 11.8 (12.3 with voltmeter check) to as low as 11.2. And the droppage usually happens when I give it gas or floor it. Now, I thought the volts would go up when you floor it because the alternator pulley is spinning faster creating more electricity? maybe I'm wrong. Please help.

I also have a post in the turbo section about a vacuum leak if anyone wants to chime in.

The original was 120A. A smaller alt would be working harder, and voltage readings would drop with all the accessories running; like the cooling fan, blower motor, rear defogger, lights and powermaster motor. All of these are high draw systems that required a larger alt. The base non-turbo Regals didn't have electric cooling fan or the powermaster.
Fix that dash bulb :biggrin:

 

[turbo39151]

120amp is stock. Do yourself a favor and upgrade to 140 amp. Better safe than sorry. Look up some of my old posts and you'll find part numbers and prices. I'm in San Diego, so prices should be relatively the same...

 

[baller760]

Fixed the dash bulb and all is well now. The battery voltage is all back up. Now that it is running right all I have to fix is a vacuum leak and Malfuncion 31? Oh, and my fuel pressure is not rising with rpm. stuck at 36.

 

[441120]

Code 31 is waste gate solenoid electrical. At the pink/black wire, key on = 12v. At purple/white no ground, if you ground diagnostic at ALDL the ECM should ground the purple/white.