I have a 98 Cherokee Classic 4x4 4.0. Randomly my battery volt reading will drop to zero and then for no reason return to normal. I have pulled the alternator and it shows to pass when tested. When load tested the voltage regulator reads low. I was told the voltage regulator is in the computer and not the alternator. I am adequate at repairs but not an expert, ideas?

 

correct, voltage regulator is in the computer.........is the gauge reading zero? or are you seeing zero on a meter?

 

No its zero, running off battery, alternator is not charging battery but alternator has passed bench test.

 

It happened again on the way to work today, tightened the bolts to the ecm and blew out the connectors. It started charging just fine with doing nothing else to it. I was thinking a grounding issue with the ecm, going to ground it additionally this weekend but will also take another look at the alternator

 

Ok, not fixed lol

 

I have no experience with this, but I'm thinking you are on the right track with checking grounds. Seems like you have voltage, then you don't; so something is loose some where, or you have a bad wire or crimp. I would check all your connections for everything. Go over the entire vehicle. It would help if you jiggle the wires while someone watches the meter too................either that or the voltage regulator is going bad inside the computer.....

 

Check and clean all grounds and cable conditions. Fire wall to Head, Battery to Body, Frame to Engine. I suggest upgrading to a higher guage cable while you are at it. It is extremely rare for the Volt Regulator inside the ECU to go out.

 

I experienced this, and it was a leak on the tstat housing spraying coolant into the alternator. voltage drop right out then come back. Advance has a great alternator tester, and is free takes 5 mins.

 

my 2000 did this today for first time, was going to work about 200 yards from house the battery gauge went to about 8 than to zero. At same time my red "check gauges" light came on. I turned around and drove my truck .so I haven't had time yet to troubleshoot the problem, will be keeping an eye on this thread. Thanks

 

had my alternator tested at 2 o'riellys and two autozones on the way to worktonight... 3 passed 4 failed. it would pass everytime on the first test and pass/fail randomly after that.soo I bought one see what it does

 

Tel Tale sign of a fading alternator. Go ahead and just replace/upgrade it.

 

yup drove into work 65 miles no problems on new alt so far

 

I added a 10 ga wire to insure my ecm was grounded and have not had another issue. If it does return I will replace the alternator