99 XJ 4.0 swapped motor, now charging at 19 volts....?

Over the weekend I pulled my 4.0 out of my 99 xj that threw a rod and put in a 4.0 from a 97 ZJ 2wd. I swapped out basically all of the brackets and accessories from my motor onto the new ZJ 4.0. I had a buddy help (that believe it or not is mechanically inclined) and he long story short hooked up my alternator plug to the ac and blew the pcm / coil fuse (21) . During this said plug obviously was not plugged into the alternator. I looked for myself and saw that it was wrong and plugged it in.

Turned jeep over and now it charges at too high a voltage. I researched and it says that the voltage regulator in the PCM may be bad or possibly the dark green wire from PCM to alternator is grounded. Because the "mishap" I am guessing it shorted the PCMS

Can anyone weigh in on this? I am thinking of finding anot her PCM to swap in.

Just add another Battery and drive it.uke:

If the alternator shows 19 volts I would first suspect a connectivity issue. Re-check all the wire connections and ground connections. Everything has to be clean and snug.

Tim_MN said:

If the alternator shows 19 volts I would first suspect a connectivity issue. Re-check all the wire connections and ground connections. Everything has to be clean and snug.

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In addition, the PCM grounds the one of the alternator field wires so it would charge. It does this rapidly to maintain a constant voltage in the battery. If that field wire is shorted to ground the voltage would/could go as high as 19 volts. One of the two wires is a constant positive 12 volts when the engine is running. The other is grounded by the PCM to turn the charging on and off. Check the alternator to see if it have an internal short to ground.

I ordered a Dodge external voltage regulator from napa to try it out and bypass the PCM. Seemed fine hooked up to the alternator pigtail and to 12v source till I was driving it home from shop (I work at a body shop) and then it crept up to 19 so I shut it off. Turn it back on and it's fine.... for a while then same thing. The PCM wires are capped and go no where. The grounds from body to engine and battery to body look fine, I even roll locked the past off the firewall to ensure metal on metal.

I'm feeling like it has to be alternator issue at this point. Any insight anyone else can share would be great

If the dashboard gauge shows 9 volts, there is an alternator issues, typically worn brushes. Often stopping and re-starting the engine or just hitting a bump in the road will temporarily restore charging. If the dashboard gauge shows 19 volts, there is almost always a connectivity issue that needs to be diagnosed by a thorough visual inspection and testing with a volts/ohms multi meter.

The battery gauge going to 19 volts indicates a connectivity issue in the charging system.

Perform routine maintenance of the start and charge systems. Remove, clean, and firmly reconnect all the wires and cables to the battery, starter, and alternator. Look for corroded or damaged cables or connectors and replace as needed. Copper wires should be copper color, not black or green. Battery terminals and battery wire connectors should bright silver, not dull gray and corroded. Do the same for the grounding wires from the starter to engine block, the ground wires at the coil, and the ground wires from the battery and engine to the Jeep's frame/body. You must remove, wire brush, and clean until shiny the cable/wire ends and whatever they bolt onto.

Jeeps do not tolerate low voltage, bad wire connections, or poor grounds.

Place your DVOM (Digital Volt Ohm Multi-Meter) on the 20 volt scale. First check battery voltage by placing your multi-meter's positive lead on the battery's positive post ( the actual post, not the clamps ) and the negative lead on the negative post. You need a minimum of 12 volts to continue testing. Next, leave your meter connected and take a reading while the engine is cranking. Record this voltage reading. Now connect your positive lead to the battery terminal stud on the starter and the negative lead to the starter housing. Again, crank the engine and record the voltage reading. If the voltage reading at the starter is not within 1 volt of battery voltage then you have excessive voltage drop in the starter circuit.

Typical voltage drop maximums:
• starter circuit (including starter solenoid) =0.60 volt
• battery post to battery terminal end = zero volts
• battery main cable (measured end to end) 0.20 volt
• starter solenoid = 0.20 volt
• battery negative post to alternator metal frame= 0.20 volt
• negative main cable to engine block = 0.20 volt
• negative battery post to starter metal frame =0.30
• battery positive post to alternator b+stud =0.5 volt with maximum charging load applied (all accessories turned on)

Test the output at the alternator with your volts/ohms multi-meter. You should be measuring 13.8-14.4 volts. Load testing the alternator is still recommended.