welderman1969

Good morning all !
1990 jeep cherokee 4x4 renix , 4.0 automatic . I have had this charging problem with this jeep since I have got it ! I have replaced batteries 2 now and 2 new alternators . Everything new in it twice now . To no solutions . I have taken all electtical connections apart and cleaned them . I have add 4 gauge ground wires to motor and the body . I have checked yellow trigger wire with ignition key on it has 12 volts. The other wire has zero reading . The problem is it only charges off and on . Sometimes it charges at 14 volts other times the gauge is clear down in the read . I have put a volt meter on battery while running and when its charging iam getting over 14 volts . But most of the time its not charging it will usually run the volts at 12.3 at battery will running . But even if you rev and hold it at 2 grand it will only show about 12.6 volts. That the way it is most of the time . But then once and a while it will kick in at charge at 14 volts . Most of the time running down the road the inside guage is in the red showing about 10 volts and the headlights r way dim ! I have run out of ideas ! Any help would be wonderfull !!
Thankis ,Brad

welderman1969

I have also replaced the starter relay . I have added 4 gauge wire from alternator to relay then from relay to battery .
Thanks again ,Brad

cruiser54

Here's something that COULD contribute to the odd readings:

Improving the Instrument Panel Ground
The ground point for the complete instrument cluster on your XJ or MJ is located up under the driver’s side dash. If you lay on your back and look up under there with a flashlight, without wearing a hat, you will see a black wire attached to a shiny piece of metal almost directly above the hood release ****. The screw will have either a ¼" or 5/16" head on it.
This ground point is responsible for handling the ground circuit for the following items: Dome lamps, Seatbelt and key warning, trans comfort switch, wiper switch, headlamp switch and delay module, fog lamp switch, cargo lamp switch, all instrument panel grounds and illumination, power windows and door locks, cruise control dump valve, and a few more things.
The problem is that where the ground point is located does not have a good contact with the chassis where the ground should be. The solution is simple.
Make up a jumper wire with #10 gauge wire about 10" long. On one end, crimp on a ¼" round wire terminal. On the other end, crimp on a 3/8" round wire terminal.
Remove the screw from the existing ground wire and attach the small terminal of your jumper so that the original wire and your new jumper share the same attaching point, one over the other.
Look above the driver’s side plastic kick panel just forward of the top of the hood release ****. You will see an 8mm stud there. Attach the large terminal end there with a washer and nut over it tightened securely.
**Special note for Comanche owners: Make your jumper wire 12" long and attach it on the driver’s side kick panel close to the fusebox on the 8mm stud.**
　
Revised 11-29-2011

welderman1969

Ok ! But how would that effect the volt readings at the battery terminals ?

welderman1969

Did the wire on dash ground . No change ! Put the lights on pulls down to red .

belvedere

Is the voltage regulator in the PCM on a '90?

cruiser54

Uh, no.

welderman1969

Ok folks any more ideas ? Or what to look for ? What would cuase the alternator to only charge part time ?
Thanks,Brad

cruiser54

Monitor it with a meter at the critical places for 12 volts/triggering and start wiggling wire harnesses.

DFlintstone

I sort of doubt this is your issue, but I'll post it anyway. Year and 1/2 ago I dropped a washer changing my Thermostat. After I gave up looking for it I found right away on firing it up it had fallen between the belt and crank pulley. Bang, the belt is a mess. So I end up with a new Kergan belt of some sort. (I needed a friend to bring me one). Tight, tighter, tightest the darn thing would slip on the Alternator pulley under load.

Finally in desperation I went out there with a bottle of Dawn dish soap and the garden hose. Idling I got it wet, then squirt soap on both sides, rinsed some and soaped more. To end I ran the hose slow on it running for over a minute at least. That solved it. There was some sort of coating on the new belt? Idk.

I normally run my belt as loose as I can, and still have the alternator not slip with the blower on high, and lights on brights. Puts less strain on all the other bearings. Radi pointed out a cool tip. After it might have been slipping, (voltage has been low), see if the Alt. pulley is hot. I need to go back and loosen mine a tad. I got it pretty tight before I dealt with the coating on the new one. I don't want to go back to the store for an idler, alternator, water pump, fan, ect, any sooner than I need to!

welderman1969

Ok folks !
Got home from work fired it up showing on inside guage charging at 10 volts threw lights and heater on dropped to almost 9 in the red ! Things pissing me off ! Has to b something simple . Where should I check for 12 volts with meter at ?
Does anyone have a diagram for this thing ? 1990 jeep cherokee ? What triggers the alternator to charge ?
Thanks ,Guys

ps sorry about throwing all of this at you guys ! But iam a diy kind of guy and this thing is kicking my but . Would love to get this fixed and start driving it !
Thanks,again for the help !!!!

wesleys1990xj

I had the same problem. You have to take the bottom panel off to see all the grounds. Clean every ground you can find. Then clean the ground going to the frame to the block.

cruiser54

Must have battery voltage at the stud and ignition voltage at the yellow wire in the 2 wire plug to excite the alternator to charge.

There's a connector behind the battery that carries the signal from the yellow wire.

EvstaG

I can't remember which one it is, but I believe there is a fuse that needs to be in place in order to allow the alternator to charge? Could there be excessive corrosion or a loose connection? I know both of these have happened to several fuses on my 89, one of which was giving me charging issues.

cruiser54

No fuse in the wiring diagram I just looked at to get the wire colors and routing.