Car wont charge, New alt. and has power going to it!!!

[juiced_94gt]

Ok well I fired up my car after a year rebuilding it AGAIN and now it wont charge, I have power to the plugs at the alt. as well as the big wire hooked up to it with the key on engine off but when I turn the car on it only runs off the battery what would cause this?? I even went out and bought a new alt. and same problem!!! I REALLY WANT TO DRIVE MY CAR so any info would be appreciated. thanks.

Mario.

 

[HISSIN50]

Mario, you didnt provide specifics with regulator testing.

First, be sure the alternator fuse in the underhood fusebox is ok. The prongs on the fuse receptacle have been known to get loose or cause issue. If this occurs, the sense circuit is hindered.

The reg is labeled A, S, I.

A is the sense circuit. It should float battery voltage with the car on or off.

I is the excite circuit. It tells the alternator to turn on. Does your battery light illuminate when you first turn the key on? If no, this might be an issue right now. With the car idling, the I circuit at the regulator should show over 1 volt.

S is the stator circuit. It is a field winding loop from the S terminal on the reg to the lone port on the side of the alt. Either end of this wire should show about half battery voltage (IIRC) while the alt is functional. If yours shows zero volts at idle, this is an issue.

Make sure the PDC connection (side of the underhood fusebox) is clean. It's a known problem area (the connections can corrode, even in nice climates).

If you run through this stuff and it's all copacetic, post up the exact DMM readings you get on the A, S, I terminals and we can run further diagnostics from there.

Good luck.

 

[juiced_94gt]

thank you hissin I will check all that today. The battery light doesent come on even when the volts get low. What does that mean? The only sign I have is that the volt guage is low.

 

[juiced_94gt]

ok here are my volt readings.

CAR OFF:
A=12.29
I=0
S=.04
little plug=under 1 volt


Car at idle:
A=11.4
I=10.8
S=9.1
little plug=9.8

And the battery light on the dash doesent turn on at all.

 

[HISSIN50]

thank you hissin I will check all that today. The battery light doesent come on even when the volts get low. What does that mean? The only sign I have is that the volt guage is low.

The battery light not coming on while the alt takes a dump isn't huge - I've had that same issue occur before. But if the light doesnt even illuminate when all the other idiot lights prove-out (right after you turn the key to run, before you try to start the car), then that can suggest that the excite circuit is compromised. If that circuit is bad, the alt doesnt know it needs to 'turn on.'

The Excite circuit uses the battery light as a resistor to pull voltage out of the circuit. There's also a 500 Ohm resistor in parallel with the bulb, just in case the bulb burns out. You can deduce that there's resistance in the circuit via the I terminal reading on the regulator.

 

[juiced_94gt]

The battery light not coming on while the alt takes a dump isn't huge - I've had that same issue occur before. But if the light doesnt even illuminate when all the other idiot lights prove-out (right after you turn the key to run, before you try to start the car), then that can suggest that the excite circuit is compromised. If that circuit is bad, the alt doesnt know it needs to 'turn on.'

The Excite circuit uses the battery light as a resistor to pull voltage out of the circuit. There's also a 500 Ohm resistor in parallel with the bulb, just in case the bulb burns out. You can deduce that there's resistance in the circuit via the I terminal reading on the regulator.

What should I do??

 

[HISSIN50]

What should I do??

Does your battery light not illuminate at all? Based on the voltage you're seeing, that seems like it might be the case.

Have you checked that the battery light's bulb isnt burned out?


If the bulb is ok, I'd consider doing a bench test of the circuit. If you open the I wire just off the regulator (there are often splices already in place from where previous owners replaced a regulator plug), connect the cut end of the I wire (leaving the reg) to a 500 ohm resistor (Radio shack has resistors that will work. You can be +/- 30 ohms or so and be fine). Then run this to an accessory source (the hot side of the ignition coil works fine for this test).

Now see if your alt works properly. If so, you need to dissect the I circuit and figure out why the power doesnt go through the bulb or parallel resistor.

 

[juiced_94gt]

IT WORKS!!! Thanks hissin for all ur help, it was the powder coated brackets that werent grounding the ALT. I simply grinded off some powder coat and now it charges at 14.3V at idle...is that ok?? and the car is running SMOOTH

 

[HISSIN50]

IT WORKS!!! Thanks hissin for all ur help, it was the powder coated brackets that werent grounding the ALT. I simply grinded off some powder coat and now it charges at 14.3V at idle...is that ok?? and the car is running SMOOTH

I musta' missed the part about it being powdercoated. Your issue is a common one and you did what everyone else does.

14.3 is just fine.

Nice work!