2005 Liberty 3.7 . With field wires plugged into alternator I get a code for # 4 injector & engine won't rev above 2200 rpm's .
Unplug field wires , clear codes & engine runs fine . Have tried two alternators & batteries & new PCM .
I read to test the alternator to see if it's charging to unplug the field wires & jumper the field terminals on the alternator , one to battery terminal on alternator & other wire to alternator case . When I tried this the injector code & no rev problem came back .
Seems like I have an overcharge problem instead of an undercharge problem or it's something else entirely . I am considering adding an external regulator kit . Any ideas on these problems ?

The alternator in my CRD is different than your 3.7. So I dont know exactly how your alternator is supposed to behave. I know my alternator has its own internal regulator and will function just fine without any input from the PCM.

If you have already tried two different alternators and got the same result (assuming both alternators have tested good) then I suspect the problem is in the wiring harness.
So check the wiring out really good. Look for any rub marks on the harness where insulation is worn away creating a short.
Thats all I can suggest.
Very strange problem.

I'm sure that adding a external regulator will help.
https://www.youtube.com/watch?v=BI7oFEcDQzo
https://www.youtube.com/watch?v=utXjxwPAcHk

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U.S. Army Retired

Bad as I hate to have to do it , I think I'm going to have to tear into the wiring harness . Part of it runs across the top of the bell housing in behind the engine heads & I can't hardly see it much less work on it . All the injector & coil wires for the right bank are in this part of the harness along with other wires . Of course the # 4 injector that's giving me the code is wired in this part of the harness .