computer controlled alternator with MS2

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computer controlled alternator with MS2

Postby olaaf » Tue Sep 11, 2012 9:26 am

Hi All

On my ford 4.6, the PCM controlled the alternator. As far as I can tell, one of the 3 pins went to the indicator light on the dash, one went to the “sense” line, connected to 12v, and one went to the PCM.

What is the function of the PCM line, and can I just lift it and not worry? I think I blew out the logic circuitry on my alternator, and I ran with the 3 pin plug unconnected. The battery is over-charging, and I need to rev the engine a little upon start up to kick in the alternator..

Any thoughts?

Thanks
olaaf
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Re: computer controlled alternator with MS2

Postby Matt Cramer » Tue Sep 11, 2012 9:50 am

I've seen several different ways of doing this. On some cars, the ECU just switches the voltage regulator from high to low voltage mode. On others, it directly controls the alternator field winding.
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Re: computer controlled alternator with MS2

Postby olaaf » Wed Sep 12, 2012 2:20 am

Hi matt

What do you generally recommend people to do with PCM controlled alternators?

thanks
olaaf
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Re: computer controlled alternator with MS2

Postby Peter Florance » Wed Sep 12, 2012 4:53 am

olaaf wrote:Hi matt

What do you generally recommend people to do with PCM controlled alternators?

thanks
olaaf

I think it depends on how the alternator functions. That will determine how to control it. Sometimes the wiring diagram will show the internal parts of the alternator. That will help.
Peter Florance
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Re: computer controlled alternator with MS2

Postby Matt Cramer » Wed Sep 12, 2012 6:04 am

Precisely - you need to figure out what the PCM is doing to control the alternator first.
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Re: computer controlled alternator with MS2

Postby elaw » Wed Sep 12, 2012 7:56 am

olaaf wrote:I think I blew out the logic circuitry on my alternator, and I ran with the 3 pin plug unconnected. The battery is over-charging, and I need to rev the engine a little upon start up to kick in the alternator..

That may be your problem right there. Regardless of what you do with the other two wires, do NOT run with the "sense" line disconnected! When you do that, the alternator may think the system is getting 0 volts and increase its output to compensate... thus overcharging the battery.

I'd try connecting the sense line to (in order of preference) the +12 "main junction point" if your car has one, or the alternator's output terminal, or the battery. Connect an indicator light to the light terminal and the ignition +12 (that'll eliminate having to rev the engine to get the alternator going), and go from there.
Eric Law
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