Need Help! Won't Start...Stuck At Work!

[pancake]

Hello Folks,

While on my way to work, this is what happened...

-Turned on Air Conditioner and it ran fine, but then the radio started to cut out.

-Turned off Air Conditioner and the problem went away

-While driving down the freeway, the battery voltage gauge jumped from the normal ~14v to 19v!!!

-I pulled over to check things out, and now it seems the battery is toast. I have no lights, no power anything, and no start.

Here is what I did this weekend...

-Changed tranny fluid and did a flush. When I removed the tranny oil pan, I first pulled the tranny dipstick tube out of the engine compartment to free up the pan. When bolting the tube back in the wrench hit part of the starter, and sparks went flying. I should have disconnected the battery, but I was in a hurry.

The Cherokee ran ok yesterday (I did the work on Saturday, today is Monday) but now it's dead in a parking lot ~2 miles from work. I searched the board, and I suppose it could be a ground wire...but could I actually have fried one of those?

I could stop and pickup a new battery since I have no idea how old this battery is (just bought the vehicle used ~3 weeks ago) but I don't want to damage a new battery.

Please help!!!!!!!!!!!!!!!!!!!!

[Lou]

Not much help, but . . .

Check main fuses, and connections to alternator, starter, battery.

[pancake]

Hi Lou,

Thanks for the response. Well, I checked those and they seemed ok to me. No blown fuses at all. *sigh*

I might try jumping it...

[ZmOz]

If your voltage went up to 19 volts, I would think it is your alternator, I don't see any other way that could happen. Maybe the voltage regulator is toasted or something...

[Matthew Currie]

Originally posted by pancake
Does this vehicle have a seperate voltage regulator? Also, what could cause the increase in voltage to 19v? I doubt it would be the alternator, but voltage regulator does make sense.

btw...I had a buddy take me to the XJ and we jump started it. It runs fine, but the voltmeter jumped back up to 19v again for ~40 seconds while I was driving, then dropped back down to 14v.

Are any of these typical symptoms of a dead battery in the XJ's?

I would guess this as a symptom of a bad battery connection. The battery acts as an additional voltage regulator in the system, and it can overcharge if the battery is either stone dead or temporarily disconnected. If the battery were that dead, though, I wouldn't expect the problem to be intermittent. First thing I'd do is a good cleanup of battery terminals, and a check of cables at both ends.

I hope it isn't the regulator itself, because that's built into the engine computer. OUCH!

[pancake]

Originally posted by Matthew Currie
I hope it isn't the regulator itself, because that's built into the engine computer. OUCH!

Oh, that ruined my day.

Why the heck would they build that into the ECU? Wouldn't it cause the computer to run very hot???

[AZ Jeff]

Originally posted by pancake
Oh, that ruined my day.

Why the heck would they build that into the ECU? Wouldn't it cause the computer to run very hot???

No, not really. You are thinking in terms of using resistors to regulate voltage, and resistors DO generate heat, but the ECU does not use a resistor approach.

All they do is turn the voltage up or down to the field coil of the alternator to regulate the voltage out of the stator windings. Nominally, both sides of the field are at 12V (battery voltage). When the ECU senses the need to charge, it drops the voltage on it's connection to the field, creating current flow through the field winding. The actual amount of current through the field coil, in terms of amperes, is fairly low, so the amount of heat generated is small.

I agree with Matthew that it could be a dirty battery connection. It happened to me a few weeks ago.

My volt meter was erratic and I could hear the engine "whirring" over the AM station I had on the radio. We had stopped to let the rigs cool a bit after wheeling them. When I went to re-start mine, nothing. I popped the hood and cleaned the negative terminal.

No probs since.

Bill90XJ

[pancake]

Well, here's the update...

I did some testing with a voltmeter, and the battery 'appeared' to be the problem. I had cleaned the terminals and connectors really well before testing. I headed to the local Autozone and had them test the battery...dead!

I bought a new battery and had them test the alternator just in case, no problems there. So, with the new battery the Jeep runs fine. The voltage spike really confused me...

Thanks for all the help!!

[DaveD in Canada]

Not uncommon for alternator voltage to jump to 18-19 volts with an open-circuit battery. Sure is hard on accessories, lights, etc tho...

[5-90]

Hey pancake -

San Jose, CA? Need some troubleshooting help? I'm here in town...

5-90

[pancake]

Doõz this Öohicle ¨mve a ster`te vilt`ge òagulator? Also, what could cause the increase in voltage to 19v? I doubd-it wou|e bd thô/alternðqor, bu¤.voltagô/regulator does@make sense.

btw...I had a buddy take me to the XJ and we jump sta²ed it.ðOt runspcind, bÔw the v>otmdter oumped âick up to 19v again for ~40 seconds while I was driving, then dropped back downà}o 04v.|
Are any nf tøkse typxmal symptomr ofph dead battery in the XJ's?