Newbie here, chasing electrical issues and pretty stumped. Any help would be much appreciated!

Symptoms: at idle all interior/exterior lights pulsate. The flickering stops once throttle is applied. Also the volt gauge will intermittently peg at 19V seemingly at random. I confirmed the battery is getting consistent 14.6v and never gets 19v like the gauge sometimes reads. Also not sure if related but the battery will completely drain after a few days of sitting. Parasitic draw test only shows about 2 mA of draw.

The jeep came to me with an external voltage regulator already installed (photo below). The PCM and external volt regulator are both simultaneously connected to the alternator field terminals. Initially I thought the external regulator was installed to compensate for aftermarket stereo/amplifiers/subwoofer that the PO installed, so I disconnected the amps/sub and simply unplugged the external regulator to see how the PCM-alone regulates the alternator. The below test is starting with a fully charged battery at 12.7v.

With external voltage regulator disconnected:

• engine idles slightly smoother, no pulsing noises, and no lights flickering.
• battery is only getting ~11.8v (confirmed with multimeter therefore it’s not charging.)
• volt gauge on dash started at 12v and dropped down to 9v after a few minutes.
• during this idle run, with blower on high and high beams on, I tested voltage drop across alternator B+ to battery positive post and got 0.063v (manual says must be below 0.6v). Then tested alternator ground stud to negative battery post which was 0.036v (manual says must be below 0.3v).
• shut engine off and battery was too dead to restart, even with external VR plugged back in. It had only been running for just a few minutes. Battery had 12.3v after shutdown.

With the voltage regulator connected: (reminder the PCM field source/driver are also connected to the alternator):

• engine runs a little rough, pulsing sounds, lights flicker/pulsate at idle
• battery gets consistent 14.6v confirmed with multimeter
• dash shows 14v and intermittently/randomly pegs to 19v for varying lengths of time.

I have all new big 7 cable upgrade, all wires resistance and voltage drops test good. I have previously gotten the alternator load tested (while installed) at Advance and it passed. Battery is new. I have already checked and cleaned all grounds in the engine bay.

My questions/thoughts:
Any ideas why my battery is draining with such a low parasitic draw reading?

The flickering lights at idle that improve with engine speed make me think weak alternator. But the lack of charging without the external voltage regulator connected makes me think bad EVR circuit in the PCM. Is there anything else I can do to test the PCM?

Anything else I’m missing?

 

Your testing proved that the PCM isn't regulating the alternator, so you need the external regulator. Pulsating power usually is related to a bad diode in the alternator. A bad diode can also cause parasitic drain. I would also look under that tape wad by the regulator, looks suspect to me.

Use a meter on AC to check for a bad diode. With the engine running test from the alternator output to ground. There should be almost 0v AC on a good alternator.

 

Without reading your whole post, pulsing at idle would suggest the battery isn’t connected. Then you said it goes dead after a few days but there’s no parasitic draw (2ma is normal)
So me thinks either your battery is really shorted bad, or your charging system isn’t getting the volts to the battery. Another thought is a bad alt. diode
Also if you don’t have switched 12v feeding your external regulator, it will drain the battery when not running. Big time.
Let me know what you think of that and then I’ll read the rest of your post..

 

Note from DJ
This may be your problem.Long story short.

I have been having intermittent charging problems on my 97 Cherokee 4.0 with stock alternator.

When alternator stops charging I pop the hood and tap on the back of the alt case with a pair of pliers (light taps do it) and it starts charging again.

When I park the jeep and start it and the alt not charging again, so I tap it and it charging again.

Sticky brushes and or slip ring needs polished up may be the problem?

 

Thanks for the replies. I should note that when the external reg is connected, the alternator outputs fine at 14.6v consistently even when the volt gauge is pegged at 19v. Also the battery is basically new and tests good.

@andjones I tested the alternator output to ground and got 0.000v AC. Does that confirm the alt diode is good?

Also that tape wad on the reg is just a splice for one of the wires and tests fine on resistance and v-drop.

The external reg has 2 wires which each run directly to the 2 field terminals on the alternator. (Plus a ground wire that runs from the reg housing to ground). That’s it. I’m not sure how that would drain the battery. @97grand4.0 what do you mean exactly by “switched 12v feeding the regulator”?

 

Your diodes appear to be good.

14.6v is pretty high, your alternator may be running full field.

A way to test this is to first find which one of the field winding terminals on the alternator has battery voltage (12v).

The other field winding terminal is the one to concentrate on (~ground). This terminal is provided a ground signal from the regulator (the alternator is regulated on the negative field winding). With the engine running and voltmeter (DC) on the alternator output terminal and battery ground, now with a separate wire momentarily ground the regulated field terminal of the alternator . Observe if there is any change in voltage output or engine load. If there is no change then your alternator is running full field (= not good). The regulator is not doing its job either because it has failed or because of improper wiring.

Look at the wiring diagrams below. These show how simple the connections are. 12v is provided to the regulator and the alternator field terminal from ignition wiring (blue and blue/white). Negative reference is provided by the regulator through the other field terminal (green wire). There should be no other connection to the green wire.

Since this is an alternator that has a ground isolated field, either field winding terminal can be used for 12v or regulated ground. AC voltage is produced either way it is wired and the diodes rectify AC voltage to DC.



Basic Mopar electronic alternator wiring.

Simplified wiring diagram.