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Alternator, good or bad?

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Old Jun 25, 2023 | 05:54 PM
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Alternator, good or bad?

This is on my '87 Formula which I recently acquired. It has some electronic gremlins I'm trying to work through.

Okay, the alternator.

12.5 V on battery, 12.5 V when car is started, 11-ish when under load , (lights, fan, radio). All connection look good. Seems like the alternator is bad. But before replacing or rebuilding I take it to the parts store for testing and it passed.

So either the parts store testing isn't picking something up like a bad regulator or something? Or my problem is not with the alternator.


Any thoughts? I'm out of ideas.
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Old Jun 25, 2023 | 06:01 PM
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Car: Resto-Mod 1987 IROC-Z Clone
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Transmission: My own built/ design 4L80M
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Re: Alternator, good or bad?

Post an Image of the Alternator showing the Electrical Connector...

Lets see what the Wires from the Connector are connected to, because it seems that the Alternator is not "Exciting"...
The Voltage Regulator Circuit may not have the correct connection.
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Old Jun 25, 2023 | 06:11 PM
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From: Chasing Electrons
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Re: Alternator, good or bad?

CS130? If so the battery is likely weak. Which in time will take out the alternator.

RBob.
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Old Jun 25, 2023 | 06:16 PM
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Car: 1989 IROC-Z. Original owner
Engine: LB9. Dual Cats. Big Cam
Transmission: World Class T-5
Axle/Gears: BW 3.45
Re: Alternator, good or bad?

Originally Posted by vorteciroc
Post an Image of the Alternator showing the Electrical Connector...

Lets see what the Wires from the Connector are connected to, because it seems that the Alternator is not "Exciting"...
The Voltage Regulator Circuit may not have the correct connection.



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Old Jun 25, 2023 | 06:20 PM
  #5  
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Car: 1989 IROC-Z. Original owner
Engine: LB9. Dual Cats. Big Cam
Transmission: World Class T-5
Axle/Gears: BW 3.45
Re: Alternator, good or bad?

Originally Posted by RBob
CS130? If so the battery is likely weak. Which in time will take out the alternator.

RBob.
How do I test that other than putting a meter on it?
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Old Jun 25, 2023 | 07:05 PM
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Car: Resto-Mod 1987 IROC-Z Clone
Engine: Alky fed L92 Vortec Twin-Turbo 6.8L
Transmission: My own built/ design 4L80M
Axle/Gears: Custom 12 bolt (4.10:1)
Re: Alternator, good or bad?

In the First Image there was the Connector Port for the Wiring related to the Voltage Regulator.

Can you Post an Image where I can see the Connector on the Alternator.
I want to see if the wires for the Voltage Regulator are present.

The Connector should look like this:




Then try and see what they are connected to...
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Old Jun 25, 2023 | 07:12 PM
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Re: Alternator, good or bad?

Originally Posted by chazman
How do I test that other than putting a meter on it?
You take it to the parts store for testing.
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Old Jun 25, 2023 | 07:15 PM
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Car: 1989 IROC-Z. Original owner
Engine: LB9. Dual Cats. Big Cam
Transmission: World Class T-5
Axle/Gears: BW 3.45
Re: Alternator, good or bad?

This?






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Old Jun 25, 2023 | 07:18 PM
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Engine: LB9. Dual Cats. Big Cam
Transmission: World Class T-5
Axle/Gears: BW 3.45
Re: Alternator, good or bad?


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Old Jun 25, 2023 | 08:38 PM
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Re: Alternator, good or bad?

I think this is related to your Choke Light issues:


I think the above is for 1985 as it matches my 1985 manual, but we know there are some differences with your 1987. However, if you're missing the circuit between the ignition switch and alternator then it will not excite at idle and the choke light will not operate correctly. This would be why the alternator is not charging in your car but passes the test at your parts store.


Originally Posted by chazman
This is on my '87 Formula which I recently acquired. It has some electronic gremlins I'm trying to work through.

Okay, the alternator.

12.5 V on battery, 12.5 V when car is started, 11-ish when under load , (lights, fan, radio). All connection look good. Seems like the alternator is bad. But before replacing or rebuilding I take it to the parts store for testing and it passed.

So either the parts store testing isn't picking something up like a bad regulator or something? Or my problem is not with the alternator.


Any thoughts? I'm out of ideas.
Reply
Old Jun 25, 2023 | 08:47 PM
  #11  
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From: Chicagoland
Car: 1989 IROC-Z. Original owner
Engine: LB9. Dual Cats. Big Cam
Transmission: World Class T-5
Axle/Gears: BW 3.45
Re: Alternator, good or bad?

Originally Posted by JT
I think this is related to your Choke Light issues:


I think the above is for 1985 as it matches my 1985 manual, but we know there are some differences with your 1987. However, if you're missing the circuit between the ignition switch and alternator then it will not excite at idle and the choke light will not operate correctly. This would be why the alternator is not charging in your car but passes the test at your parts store.
Is the circuit a dash bulb possibly?
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Old Jun 25, 2023 | 09:15 PM
  #12  
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Re: Alternator, good or bad?

Originally Posted by chazman
Is the circuit a dash bulb possibly?
It depends. The digital cluster used a hidden bulb that acted as a resistor. In the analog setup, like yours, I believe it's just a resistor wire.

The alternator not charging could be why your Choke Light is on while running. This is also why I asked about that previous post where you said you needed a jump while out driving, as that would not be normal if the alternator was charging and you didn't shut off the vehicle. The alternator needs to put out voltage to kick the choke heater relay off (electrically) and turn off the choke light. These issues are most likely related but finding out exactly the fault is difficult, especially without the proper 1987 manual or diagram. There's a lot more knowledgeable people that probably have the answer.
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Old Jun 27, 2023 | 12:43 AM
  #13  
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Car: 1987 Formula (original owner)
Engine: 305 TPI
Transmission: T5
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Re: Alternator, good or bad?

1987 Service Manual, charging system.







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Old Jun 27, 2023 | 08:24 PM
  #14  
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Car: 1989 IROC-Z. Original owner
Engine: LB9. Dual Cats. Big Cam
Transmission: World Class T-5
Axle/Gears: BW 3.45
Re: Alternator, good or bad?

Put a new alternator on. I felt it was sketchy. Failed at one auto parts store passed at another.
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Old Jun 28, 2023 | 11:26 AM
  #15  
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From: Chicagoland
Car: 1989 IROC-Z. Original owner
Engine: LB9. Dual Cats. Big Cam
Transmission: World Class T-5
Axle/Gears: BW 3.45
Re: Alternator, good or bad?

Originally Posted by vorteciroc
Post an Image of the Alternator showing the Electrical Connector...

Lets see what the Wires from the Connector are connected to, because it seems that the Alternator is not "Exciting"...
The Voltage Regulator Circuit may not have the correct connection.
Tell me more about this exciter wire. The new alternator does not appear to be charging.

Reply
Old Jun 28, 2023 | 11:36 AM
  #16  
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From: Chicagoland
Car: 1989 IROC-Z. Original owner
Engine: LB9. Dual Cats. Big Cam
Transmission: World Class T-5
Axle/Gears: BW 3.45
Re: Alternator, good or bad?

Originally Posted by RBob
CS130? If so the battery is likely weak. Which in time will take out the alternator.

RBob.
Boy, that would be so easy if it was simply a bad battery. But it tested fine at home on my meter and fine at the parts store. Maybe I'll swap batteries with another car and see what's what.
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Old Jun 28, 2023 | 03:04 PM
  #17  
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Car: Resto-Mod 1987 IROC-Z Clone
Engine: Alky fed L92 Vortec Twin-Turbo 6.8L
Transmission: My own built/ design 4L80M
Axle/Gears: Custom 12 bolt (4.10:1)
Re: Alternator, good or bad?

Originally Posted by chazman
Tell me more about this exciter wire. The new alternator does not appear to be charging.
For the Swap Guys and guys without Original Connections/ Wiring...

I offer the OEM Exciter Resistor in a Jumper Harness for Different GM Alternators:



As well as a Version with a easily replaceable socketed ATM Style Resistor:


I offer these for all different GM Alternators (as well as adapters), look for your Connector Style below:

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Old Jun 28, 2023 | 03:23 PM
  #18  
chazman's Avatar
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From: Chicagoland
Car: 1989 IROC-Z. Original owner
Engine: LB9. Dual Cats. Big Cam
Transmission: World Class T-5
Axle/Gears: BW 3.45
Re: Alternator, good or bad?

Originally Posted by vorteciroc
For the Swap Guys and guys without Original Connections/ Wiring...

I offer the OEM Exciter Resistor in a Jumper Harness for Different GM Alternators:



As well as a Version with a easily replaceable socketed ATM Style Resistor:


I offer these for all different GM Alternators (as well as adapters), look for your Connector Style below:
They look great, but I'm not sure that they would solve my issue.
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Old Jun 28, 2023 | 06:55 PM
  #19  
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From: Chicagoland
Car: 1989 IROC-Z. Original owner
Engine: LB9. Dual Cats. Big Cam
Transmission: World Class T-5
Axle/Gears: BW 3.45
Re: Alternator, good or bad?

Just so I am 110%, I switched batteries with another car and no difference.
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