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Old 08-31-2010, 12:33 PM   #1
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Default 1990 Jeep Cherokee Low Voltage Problem

I have a low battery voltage problem when I am running the head lights and blower on high speed. I have changed the alternator but the problem still exist. Where does the alternator get it charging voltage reference for the voltage regulator? Is the alternator voltage regulator controlled by the ECM?
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Old 08-31-2010, 01:58 PM   #2
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exactly what kind of low voltage problem are you having? when driving at night do your headlights dim when ever you turn on another accessory? If so, and you do in fact have a new alternator, have your battery checked first. Have a load tester put on it to make sure it doesn't have a problem before looking elsewhere.

If the battery is not the problem then the next thing you should check is all the grounds, starting with the battery cable. don't just look at it, unbolt it, clean it to bare metal, and bolt it down tight. Make sure the ground is connected to the motor too.

Hope that helps.
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Old 09-01-2010, 08:23 AM   #3
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The battery is new and all battery terminals are clean. The low voltage problem occurs when the head lights are on and the fan inside the vehicle is on high speed. It appears that the alternator is not sensing the low voltage.
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Old 09-01-2010, 08:34 AM   #4
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I've had a few "new" batteries in my time that have had a bad cell and won't fully charge. It looks fine and starts the motor, but when a demand for current rises it fails. So before you do anything else check the battery

Also, you keep say you have low voltage, how low? How are you checking it? Where are you checking it? Have you checked the gound cable from the battery to the motor and frame/body?
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Old 09-01-2010, 09:34 AM   #5
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man its all 1990s from what ive researched. I wanted to do the zj swap but its for post 93's or something like that. you probably have a 65a alternator like me and they cant even handle the normal load. you have to pay like 150+ dollars for one of those 130+a alternators
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Old 09-01-2010, 01:23 PM   #6
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I have had this problem for several years and always thought that something was wrong with the orginal alternator that can on the vehicle. Changing out with a new alternator did not solve the low voltage problem. I will check to see how much current output the alternator is putting out with the head lights on and the inside blower on high speed. I will also check the ground connections on the motor but I beleive these connections to be in good shape but it never hurts to check. Does anyone know if the ECM has anything to do with voltage control on these alternators?
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Old 09-03-2010, 06:52 AM   #7
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on the 90's the alternator is internally controlled i believe in 93 or somewhere around there they went to a PCM controlled alternator, that is why us guys cant do the zj swap. Mine does the same thing, it actually drops down in the red if i put lights and blower on high, but i can shut it off and it starts up prefect, no hesitation nothing, I am replacing my cables with larger gauge. I also read that on the older style the gauge is reading after everything is drawn from the system, not at the alternator. Because my gauge will say 10 volts, but i can check the alternator and its at 13.4
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Old 09-08-2010, 03:02 PM   #8
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I did some more checking this past weekend. With the inside AC Blower on high and head lights on the alternator is putting out 45 amps and the voltage at the battery is 14.01 volts. The volt meter on the dash is on the low side where the red starts. At this point the turn signals blink at a very low rate. As soon as I turn the head lights off and leave the AC Blower on high the volt meter on the dash comes up to about 13V and the turn signals blink at a faster rate. The battery voltage is still around 14.01 V. It appears that I am getting a large voltage drop in the wiring to the accessories with the head lights on and the AC Blower on high. Any ideas what could be causing this. The alternator is keeping up with the load demand so I see no problem with it.
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Old 09-09-2010, 06:52 AM   #9
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it is not the alternator itself, if you look at your battery cables, one goes to starter, and other that little bitty thing to to solenoid that it where everything is drawn from, now in the new models battery cable goes to a fuse/relay junction box, that why i am upgrading my cables because that little 4 or w/e gauge is not enough
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Old 09-09-2010, 07:19 AM   #10
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the stock 1987-1990 alternator is like 85-90 amps and the 91-96 is only 90 amps. the 91-96 (H.O. system) can use the 136 amp alternator off a 97-98 grand cherokee limited or the 98 dodge durango. it requires a little grinding on the original bracket to fit but it works great.
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Old 09-09-2010, 11:30 AM   #11
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I have already upgraded my cable size from the battery + terminal to the fuse/relay junction box. I think the problem that I am having is beyond the fuse/relay junction box. Does anyone have an electrical diagram of the wiring from the fuse/relay junction box? When I show low voltage, close to the red line on the low side of the meter on the instrument panel, I have 14.01 V at the main terminal of the fuse/relay junction box. I could not determine from the actual vehicle wiring where the four wires go that are individually plugged into the relay. Could there simply be something wrong with the fule/relay junction box?
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Old 05-19-2013, 11:21 PM   #12
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Ok so when i first start my 96 jeep cherokee first thing it runs for 2 sec then stalls. give it gas and its good for the time being. Ive checked the battery and replaced the alt. still happening. its been getting more and more closer together as far as the problem but now my radio loses memory and the dome light stays on after i have all of the doors closed and lights off. ive looked for shorts and cant seem to find any. can any one help me out with this?

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Old 05-19-2013, 11:54 PM   #13
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"sort of" read the thread...yea, the regulator is internal at least to 90.

Sort of a long story here. Upshot, my new belt seemed to have some gunk or coating. Supper tight the voltage would drop with a load. (blower, brights ect). I've done lots of years with these Jeeps, seems the alternator/voltage is the first place a slipping belt shows. It may or nay not "cherp".

So, exasperated, as sort of a last resort, idling, with a hose on low and a bottle of Dawn dish soap I went at it. Got it wet, applied soap to both sides, rinse, repeat. Then finished with a good long rinse. Problem solved. Idles over 14 with everything on.

I like my belt as loose as possible to curb wear on all those bearings. That was months ago and I still haven't gone back and loosened it some.

Radi had a cool idea. See if the pulley is hot. I might start it cold, turn every thing on for just a couple minutes, then check and see if the alternator pulley is hot.
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Old 05-20-2013, 08:24 AM   #14
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How about this? No mention of grounds. Only battery cables.


Renix Ground Refreshing
The Renix era XJs and MJs were built with an under-engineered grounding system for the engine/transmission electronics. One problem in particular involves the multiple ground connection at the engine dipstick tube stud. A poor ground here can cause a multitude of driveabililty issues, wasted time, failed emission tests, and wasted money replacing components unnecessarily.
The components grounding at the dipstick tube stud are:
Distributor Sync Sensor, TCU main ground, TCU "Shift Point Logic", Ignition control Module, Injectors, ECU main ground which other engine sensors ground through, Oxygen sensor, Knock Sensor, Cruise Control, and Transmission Sync signal. All extremely important stuff.
The factory was aware of the issues with this ground point and addressed it by suggesting the following:
Remove the nut holding the wire terminals to the stud. Verify that the stud is indeed tightened securely into the block. Scrape any and all paint from the stud’s mounting surface where the wires will attach. Must be clean, shiny and free of any oil, grease, or paint.
Inspect the wire terminals. Check to see that none of the terminals are crimped over wire insulation instead of bare wire. Be sure the crimps are tight. It wouldn’t hurt to re-crimp them just as a matter of course. Sand and polish the wire terminals until clean and shiny on both sides. Reinstall all the wires to the stud and tighten the nut down securely.
While you’re in that general area, locate the battery negative cable which is fastened to the engine block just forward of the dipstick stud. Remove the bolt, scrape the block to bare metal, clean and polish the cable terminal, and reattach securely.
Another area where the grounding system on Renix era Jeeps was lacking is the engine to chassis ground. There is a braided cable from the back of the cylinder head that also attaches to the driver’s side of the firewall. This cable is undersized for it’s intended use and subject to corrosion and poor connections at each end.
First off, remove the cable end from the firewall using a 15mm wrench or socket. Scrape the paint off down to bare metal and clean the wire terminal. Reattach securely.
Remove the other end of the cable from the rear of the head using a 3’4" socket. Clean all the oil, paint and crud from the stud. Clean the wire terminal of the cable and reattach securely.
A suggestion regarding the braided cable:
I prefer to add a #4 Gauge cable from the firewall to a bolt on the rear of the intake manifold, either to a heat shield bolt or fuel rail bolt. A cable about 18" long with a 3/8" lug on each end works great and you can get one at any parts store already made up. Napa has them as part number 781116.
A further improvement to the grounding system can be made using a #4 cable, about 10" long with 3/8" terminals at each end. Attach one end of this cable to the negative battery bolt and the other end under the closest 10mm headed bolt on the radiator support just forward of the battery. Napa part number 781115.
For those of us with Comanches, it’s very important to remove the driver’s side taillamp assembly to access the ground for the fuel pump. Remove the screw holding the black ground wire. Scrape the paint from the body and corrosion from the wire terminal. Reattach securely.
If you want to upgrade your grounds and battery cables in general, contact Jon at


www.kelleyswip.com. He makes an incredible cable upgrade for a very reasonable price.
 
Revised 03-04-2013
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Cruiser's Mostly Renix Tips can be found in the pink link below:

An index to over 25 helpful write-ups is in Post #1.


http://www.cherokeeforum.com/f51/cruiser54s-mostly-renix-tips-153657/

Refresh*Connections*Before*Replacing*Components
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Old 05-20-2013, 08:25 AM   #15
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Also this. Those signals run through some pretty old connectors.....

I suggest unplugging EVERY electrical connection in the engine bay you can find, whether engine related or not, and spraying it out with a good electronics cleaner, visually inspecting the terminals making sure they haven’t retracted into the plastic holder, and then plugging it back together. There’s a critical 10-pin connector for the front lighting system located in front of the air cleaner and behind the left headlight assembly. Don’t miss that one
. Also be sure that the connectors to the ballast resistor mounted near the air cleaner housing are clean and tight.

ALL of the relays should be removed, the terminals wire-brushed until shiny, and the receptacles sprayed out with contact cleaner. Then plug them back in. I do this on every Renix Jeep I purchase or work on for someone else.

Revised 07/23/2012
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Cruiser's Mostly Renix Tips can be found in the pink link below:

An index to over 25 helpful write-ups is in Post #1.


http://www.cherokeeforum.com/f51/cruiser54s-mostly-renix-tips-153657/

Refresh*Connections*Before*Replacing*Components
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Old 05-20-2013, 08:25 AM
 
 
 
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