Alternator back feeding, FI no shut off

[tedlovesjeeps71]

I’ve been tinkering with my Jeep (83 scrambler, 360 from a Waggy) and am a little curious. It’s been a bit fussy and somehow managed to melt the starter solenoid.



I got the Jeep running and had to put a call out to Bill (Thanks Bill!!) at Hamilton fuel injection as he built the kit and knows everything. The issue is when I turn the Jeep off it keeps running. Bill kindly explained that the alternator is back feeding the system. He suggested installing a diode in the wiring going into the alternator to end that issue.
I have a couple questions about this:
What causes this to happen?
Would an aftermarket,high output alternator amplify this issue or do they have some sort of built in system to prevent back feeding?
What kind of diode do I get and which wires does it go to??
Any help is appreciated guys.

[sonoraed]

http://www.madelectrical.com/index.shtml
always liked this guy's website when I need a refresher, usually something melted means high resistance i.e. corrosion, grounds,under size cables,etc

[tedlovesjeeps71]

Thanks sonoraed...
So the cables are new, I build them out of HD wire. So are the battery terminals. Grounds etc were all addressed as part of installing the fuel injection.
Not really sure why an alternator would back feed and cause the injection system to keep running but didn’t do the same when it was carbureted? Maybe just a small amount of voltage is enough for the injection to keep going vs the carb? No idea.

[BCRAWLER]

Suggest changing where you are getting power for computer for FI. Had the same problem with the cooling fan on a car years ago. Had it wired into the ignition system so when I turned off spinning fan continued as a generator. Think you may have wired into charging system.

[tedlovesjeeps71]

Suggest changing where you are getting power for computer for FI. Had the same problem with the cooling fan on a car years ago. Had it wired into the ignition system so when I turned off spinning fan continued as a generator. Think you may have wired into charging system.

Yeah, I’ve wondered that as well. I realize when I was searching for a key on 12v I did so with the original ignition brain box still hooked up. I wonder if trying that again without it connected will point me towards a different source I can use (even though it obviously works).

[Stuka]

Why not use the source that the old ignition box used? Its a pretty heavy gauge wire, and was intended to power the ECU.

[sonoraed]

https://www.gopainlesswiring.com/produc ... diode-kit/
here's painless wiring's solution

[tedlovesjeeps71]

Why not use the source that the old ignition box used? Its a pretty heavy gauge wire, and was intended to power the ECU.

Not sure which one was it? I’m working overtime this week so I may get some time to tinker next Sunday. Maybe. The diode seems like the easier fix but I may poke around some more with the ole test light.

[tedlovesjeeps71]

https://www.gopainlesswiring.com/produc ... diode-kit/
here's painless wiring's solution

That’s only one diode. I wonder which of the alternator wires it goes on?

[Stuka]

Why not use the source that the old ignition box used? Its a pretty heavy gauge wire, and was intended to power the ECU.

Not sure which one was it? I’m working overtime this week so I may get some time to tinker next Sunday. Maybe. The diode seems like the easier fix but I may poke around some more with the ole test light.

Well, colors aren't always accurate with AMC, but from what I can see its the same for CJ and FSJ, for both i6 and V8. Typically its a red wire with a white line that goes to the old duraspark module. Its heavier gauge than the other wires. I used it to power the HEI on my J10, and can be used to power your EFI box.

[Hspencer]

When I installed my Holley sniper I used the yellow wire going to the ignition module. I didn’t have any run-up issues until I installed the Holley ignition system. Apparently there is just enough residual current from the brown exciter wire coming from the alternator to keep the ignition energized. A diode took care of the issue.


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