When I've seen both the P0340 and P1391 together, my experience is that the root cause has usually been with the camshaft position sensor circuit. The "circuit" includes the sensor, connector and all associated wiring, not just the sensor itself. Know that it is possible that testing of the cam sensor passes, but you still have an issue with it. I've seen that scenario before.

But with that being said, you gotta get that voltage situation resolved. That is job #1. It is possible that you have 2 separate issues, but it's also possible that they are related so I'd get a handle on having consistent voltage first and see if that resolves your codes, if not then consider replacing your cam sensor with a genuine Jeep sensor.

Also know that alternators can pass parts store's bench tests, but fail under the load of being installed on the engine. Not uncommon. I had one XJ where the guy installed 2 alternators and was still having problems but passed bench tests. I installed an alternator from a different vendor and all good. So be sure not to get tunnel vision as new parts can fail.

Good luck and keep us updated!

 

Battery gauge going to 9vdc is NOT overcharge, it is undercharge or worse, since if the alternator quit the battery would be the only thing it reads, and if you battery is at least 12v that shows a short or a battery that is seriously unable to even temporarily take over the load of the running vehicle. You need to get the alternator and charging system tested IN VEHICLE. Such a test is available no charge at advance auto or autozone. I suggest some place that you have not already been to.

 

When I put the battery and alternator back in I did notice that it took a few minutes for the alternator to start charging the battery. The gauge was showing low voltage. When it did start charging it went right up to 18+ volts at the battery. Might try to get it somewhere to load test the battery and alternator just don't want to cause any damage with it over charging like it is.

 

18v is dangerous to drive or even run, might damage electronics pcm etc.
I would ..what would I do...
First I would make sure I was getting 18v at the battery lead POST and not the terminal, to rule out just a bad connection to the battery. If your end is not making connection to both posts of the battery I think you might read 18v at the battery terminal as it is trying to charge a bettery that isnt there.
Then check the cables to ground with a voltmeter, make sure there is solid connection in the - and + path from the alt to the battery.
Then if that wasn't it I would bring that alternator back and exchange it. Then try again. Make sure all the little connections are tight, the pain in the rear ones under the alternator to ground, etc. Clean the terminals on the harness that connect it very well, make sure the little nuts go on nice and not cross threaded,...Jeep stuff is so rebuilt and in demand that it is more common than other makes to get a bad rebuild.

 

I will recheck all my connections when I get home. I can get a denso alternator from Rockauto for less than $100. Might try different alternator all together

 

18v sounds like the open circuit charging voltage from a running unconnected alternator. Battery terminals? I suppose a bad alternator will do the same thing.

 

Battery terminals are fairly new and clean no corrosion. All my connections are tight I took them all off and cleaned them with dielectric cleaner and reinstalled. Still getting the overcharging. I'm going to try another alternator and if that doesnt work I guess Ill look into tracing the wire from the computer to the alternator.

 

I wouldn't pull out the parts cannon just yet.

When you say overcharging, you are SURE you are reading at the battery posts themselves, correct? Not the cable ends,... you have the probes of your voltmeter on the LEAD POSTS of the battery, NOT THE CABLE ENDS OR ANYWHERE ELSE correct? If you read 18v there, you are indeed overcharging and dangerously so. That battery could explode. Bear that in mind while working around it.

IF you do in fact read 18v at the battery terminals, then the battery itself, alternator, and pcm are all possible suspects.

What is the battery voltage, to the tenth of a volt, with the engine not running, as measured with your digital voltmeter on the battery posts?

 

Yes I am reading 18.54 volts at the battery post not cables. After I shut the jeep off I am reading 13.47 volts at the posts but it slowly goes down to around 12.7 or so

 

OK then it SEEMS to me the battery is being overcharged, and it is responding as a good battery would when subjected to such overcharging. No doubt the alternator is putting out the full field on current, which is 70, 90, or whatever the amps of it are. That is alot of juice and I would not even drive it. you could end up with a fire.

What is confusing to me is you said you had the alt bench tested?
I know what a bear it is to change the alt so thats what Im trying to avoid for you, but...The only thing I can think of other than a bad alt or pcm...

What would happen if you disconnect the two wires down bottom that go to the field?
If you try that and then start it and see if it's still full charging, then hands down it's a bad alt. That's probly the easiest test for you now.

If on the other hand you disconnect the field connections, and it is NOT charging whatsoever, you still havent solved the problem, but it does point to the pcm. You could try carefully measuring the voltage across the field harness wires with your dvm while the vehicle is running, if you are careful enough under there, and if you see something like +12 steady on the dvm, then for sure the signal from the pcm is hosed. It is either miswired or shorted to a +12v source, or the regulator in the pcm is blown shorted.

 

Another thing to look at is the battery voltage after it sits a while..say 1-3 hours.. If it drops way below 12 somewhere, and quickly, it is possible the battery is bad. But if after a few hours it still is up around 12.4-6 I say that puppy is good. I would consider this only after doing the above steps.

 

I just changed the computer about a month ago because of the overcharging thinking that is where the problem was coming from but it didn't change anything. This afternoon when I get home I will unplug the 2 wires and start it and check the voltage. if its not overcharging then what does that mean bad alternator or computer? what is the best way to test the field harness wires?

 

So i unhooked the cables going to the alternator from the computer and no overcharging at the battery. Put my meter in the plug and read right at 12 volts for a good minute or 2. Does this mean my computer is bad or could it still be bad alternator?

 

Good job. So this means your alternator is working great. That's the good news.
Now you have to figure out why the plug has 12v across the terminals. One is ground, the other is supposed to be a varying signal from the regulator in the PCM. That varying voltage on the field terminals of the alternator is what increases or decreases the alternator output. Fixed 12v will give you nothing but the full output charging of the alt.

So basically if you figure out which pin of the PCM is the alternator output, and it is the same 12v you see at the harness, the pcm is bad. If you trace the wire in between and find it ok, replace the pcm. You might get lucky and find it either miswired, or shorted to a 12v wire somewhere. But it should not be 12v all the time on that wire, that will cause full output of the alternator.


12v on the plug is energizing the fixed coils inside the generator, called the stator, which creates a magnetic field that opposes the one in the rotor, and the spinning rotor inside the energized stator cuts across the now full strength magnetic field and produces the max amount of current.

 

So looking at the jeep at night I saw an arc close to the fuel rail from the wiring harness. I took the plastic and little bit of tape that was on it off and inspected the wires. I saw no bare wire or anything. Wrapped them back up good and got it off the rail. Fired the jeep up and no overcharging at all. Everything seemed fine drove in around for 8 miles or so let it sit at idle for 30 minutes and everything was good. Got in it this morning to drive it to work and at first everything was good then all of a sudden the voltage dropped on the gauge. I checked it at the battery with my meter and it was only showing a little over 12 volts. Its like the alternator just stopped putting out. THis is frustrating. Could it be just a bad alternator?