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alternator issues with 4.2 to 4.0 stroker swap

Crockodotsky

Crockodotsky

Basic User
City
Sarasota
State
FL
Guys,

I'm pulling a brain fart here with my Scrambler build. I bought a 4.0 block from a '99 Cherokee a few years ago and it had a Denso 2 pin alternator with serpentine accessories. I can't get the alternator to make any power but it just tested out fine at a local parts store. It's grounded through the A/C/Alternator mount and the main lug goes to the battery side of the solenoid. I believe the #2 pin goes to the IGN but I've tried both. #2 pin is to the right when facing the back of the alternator. The other pin is not used but I guess it could go to a light or gauge. The parts guy said that this alternator uses an external regulator. I can get one later but I cant even get this thing to make 12.5 v.

What am I doing wrong here?

Thanks!
 
If i remember correctly the Cherokees of that era used the ECU to control the charging of the alternator and the ECU acted as the regulator.
If my memory is right then your parts guy is correct and it will need some external help to make it work, either through the proper ECU or no doubt there is some aftermarket kit out there if this has happened to people before?.
 
I get that the ECU would "regulate" the charging but shouldn't a simple alternator make power on its own?

Could you recommend an alternator that doesn't need an outside source to work but also has a serpentine pully?

Thx
 
If i recall, Painless Wiring Harness Installation Manual has a detailed write-up for various alternators. If you don't find it online, i can get it when I get home.
 
Crockodotsky said:
Guys,

I'm pulling a brain fart here with my Scrambler build. I bought a 4.0 block from a '99 Cherokee a few years ago and it had a Denso 2 pin alternator with serpentine accessories. I can't get the alternator to make any power but it just tested out fine at a local parts store. It's grounded through the A/C/Alternator mount and the main lug goes to the battery side of the solenoid. I believe the #2 pin goes to the IGN but I've tried both. #2 pin is to the right when facing the back of the alternator. The other pin is not used but I guess it could go to a light or gauge. The parts guy said that this alternator uses an external regulator. I can get one later but I cant even get this thing to make 12.5 v.

What am I doing wrong here?

Thanks!
Click to expand...
A couple quick possibilities to check...
Are you certain the engine block has a good ground to the frame/battery negative post?
(Just wondering if the ground strap was installed when the engine swap was done)

Alternators have to be "excited" to create output voltage, some are self-excited others have external sources, not sure what you have.
I remember on our old "deuce and a half" brush trucks you had to get the RPM of the alternator above a certain speed before the alternator would produce voltage. They were multi-fuel engines and that RPM was higher than one would normally run the engine.

Anyway, if the alternator is not getting "excited" that could explain it testing out good but not working in the vehicle.
 
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