alg

yes ok, but remember that I have been running the engine without the alt charging the batt. so the voltage will deplete the longer I run with out charging it. The alt. has not been in the circuit since I disco the control wire. charge current dose not get to the batt. as long as the alt is not sending it.

alg

BTW I have not recharged the battery although I have run the engine a few times for several min. It starts fine under the current voltage of the batt. without me charging it. So the engine runs only on battery. thats why the voltage is low. I will recharge it.

97grand4.0

YEah it should be charged if they are going to test it. Just making sure the batt and alt are absolutely working.

alg

well, I had both checked alt, and batt. all good here. So at this point I recon I should lean to the PCM. would you agree. I had the batt. discoed for several hours hoping that what ever would reset itself. but no, all is the same. I tried to get a obd code read and zero readings But I did not expect any cause I had shorted out the pos and neg batt wires a while ago when I had them off the battery. hoping that this would force something to happen.

97grand4.0

Yes my friend it is looking like it's telling the alt to put out maximum. Only other thing I would do just for kicks is to measure the voltage at the 2 field terminals of the alternator. One is bolted to the ground, the other comes from the regulator in the pcm.
If it is putting out max voltage, then you should also see it telling it to do so, that is, you would have B+ voltage (whatever the running system voltage is) between these two field terminals. Even though I think this is a pulse width modulated signal coming from the pcm, full blast is full blast and it should be at or pretty close to the system voltage if in fact it has failed in the on position.. If in fact that is what you see when it's charging at the +18vdc, barring a short to a hot wire somewhere in the loom, then the only other likely candidate is the regulator. You could also google to find which pin on the pcm is the regulator output and check there. Any chance you spliced some wires and got them wrong recently?
The only solution then is to replace the pcm or, what I would consider, is order one of those regulator kits, you can watch Utubes on this fix and some will tell you how to make your own for under $20, since I think, THINK, your '99 requires flashing with vin and mileage to pass inspection. Otherwise you could just pop one in from a junkyard, which, if it's cheap enough, you might just do to see if it works.

alg

Good advice. I am trying to locate on the net a wiring diagram for this car. So far no luck. With It i was hoping to see if I could figure out if there is a short somewhere along the line. But I need to get my hands on a diagram. I am real good a electrical, cir. I am a licensed electrician along with years of experience in the electronic repair business. Electric is in my blood. but with out the diagram Its like getting lost in a city I have never been b/4 I just afraid that doing a patch fix might bring trouble in the future. I can get a PCM from a place in FLa. flashed and plug and play for 169.00 which is cheap enough. With warranty. I will look into the eBay regulator fix. Maybe its worth just as an experiment. But remember my volt/amp gauge is also not working. So If I need to reference it as I travel and its not working I might be screwed on the road not knowing if the batt is charging.

alg

If you recall I said that on the plug which connects to the rear of the alt. I was getting 11.4vdc I dont know what that is telling the alt to do. I which I knew what that input should be. FYI

alg

Thats funny, thanks for your message. This is a 99 grand cher. the alt has a positive charge wire going to the batt. located at the top of the unit. on the rear there is a plug with two wires about a 18 ga. that's the plug I am referring to that has that 11.4 v on it. This is the wire I suspect goes to the PCM unit. but where dose it go on the PCM. there are 3 connectors on the unit. which is its wires are in a big fat harness. If I had the man. I could easily trace. So my search goes on. All this knowledge and I cant get it done. so frustrating. I just dont want to drop 2 bills on an experiment without being somewhat sure of its outcome.

97grand4.0

I copy this from another thread I subscribed to, hope the OP doesn't mind the plagurism ..

Originally Posted by CCKen
It is from my 1999 XJ FSM.
You can go to Pacific Coast Manuals and download a pdf copy of your Factory Service Manual. Only $7.95.
Here's the Grand Cherokee section -
http://www.pacificcoastmanuals.com/j...e_manuals.html

dave1123

Hell, no! I copied it from Fred NOAZZ. I tell everyone about it. Best investment I ever made! (That is if you're referring to me.)

alg

thanks for that info. downloading it now. hope this can answer some of my questions

97grand4.0

I found this Utube, and thought the guy knew something, until the end when he checks the charging voltage with his DMM set to the AC scale....I thought we could all use a little chuckle..

alg

that you tube thing was good. thanks for the chuckle. I needed it. So here is the latest and greatest. I was looking in you tube came across one that took the PCM apart. It looks on the video that there is a long plug which has a history of failure on the solder term.
So since I have nothing to lose I took it out opened it like a otter opens a clam. and no ###n plug. ok so I checked all the solder points they looked fine. that's all you can do. put it back in the case put it back in the car. now the car will not start. cranks but no start. .............shoot me now.
So I guess I will order a PCM tomorrow.

97grand4.0

So the troubleshooter, that had to have a manual, now wants to guess the pcm has failed...you're letting me down here

alg

No............ I did trace wiring to see if a short existed. None found. The manual dose not give me operating voltages at points in question or Resistance reading either. so when I do get resistance reading I don't know if its in the range it should be. That made me take the PCM apart to see if there were an abnormal conditions internally...burned out components and the sort. Not finding anything wrong. I reassembled it and reinstalled it. and upon trying to start the car, no it will not start. So this makes me think its the PCM. would you not agree?