Weird Voltage Issue

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SwampSurvivor

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Vehicle is my PoS 2000 Jeep Cherokee. I am quite close to sending the thing to the scrap yard. Tired of it constantly breaking down.

Driving home tonight, I noticed the headlights were flickering. Then the voltage gauge went all the way to the max and Igot a check gauges light.

I got home and shut it off and went to restart it and it would just click the starter solenoid but not enough juice to turn over. I was able to get it to start (but it cranked verrrrrry slow) and when it started, voltage was at 14. As soon as turned on the head lights and blower motor it dropped down to 12, gavei t more revs and it was back at 14.

Obviously Iam going to pull the battery out and charge it tonight.

Any ideas on this|?
 
Probability Is high that its a bad voltage rectifier. Could be a dead cell in the battery. Do a charging system test at a parts store, or shop if available
 
Where would the rectifier be in an ECU regulated system?

I am going to clean the cables tonight.

I think the battery may have lost a cell. Really strange that it was find when I started the Jeep to head home and it just died on the highway like that.

Oh well. I will recharge the battery and clean everything out tomorrow night and see what happens.
 
Where did you get the alternator from?

My mechanic is a Jeep guy, daily drives a Comanche. He's had so many issues with O'Reilly alternators not just with his Jeep buy with all types of other cars that they work good out of the box then die or are dead out of the box.
 
Originally Posted By: Chris142
Clean the cables


Yes, these vehicles are pretty sensitive to this.
 
IT is likely the rectifier problem from the alternator, this will typically need to replace the chip inside the alternator. It is a simple job if you can get the same chip and handy with the tools.
 
Your battery is toast.

You may have other problems, but your battery is toast.

Any evidence of boiling near the vents?

If you short a cell, you're charging the remaining 5 cells with 6/5 the voltage they're supposed to see, and they hate that.
 
Originally Posted By: eljefino
Your battery is toast.

You may have other problems, but your battery is toast.

Any evidence of boiling near the vents?

If you short a cell, you're charging the remaining 5 cells with 6/5 the voltage they're supposed to see, and they hate that.


That's what I'm thinking too.
 
You need to test the battery after charging it. Do you have a carbon pile load tester? Or one similar to Midtronics.

The alternator will still have a 6 diode bridge as it puts out 3 phase AC that needs to be converted.


A alternator rebuild shop will have an oscilloscope to look at the output waveform.
 
Last edited:
Now that I think of it yeah also have the battery tested.

My dad had a 2004 Silverado Duramax (dual batteries) and he had 2 Optimas in it. One day the voltage was all the way up on the gauge, like 19 volts and it turned out one of the Optimas died and screwed up the voltage. New batteries under warranty replaced and it was fine for years afterwards. Also cranked a lot faster with 2 new batteries.
 
Back! Jeep was supposed to go on an offroading trip but did not want to.

Battery is from 2012.
Alterantor is new from Advance Auto (Jeep took a swim in September)

I went to start it today and the voltage was 12.5. Interior lights were good. I hit the starter and everything went dead. I think the battery is shorted.

Last night\ Idid get it started after the pegged volt meter thing. It wouldn't keep 14 volts.

I threw in a battery that I have from 2007. It had 12.3 volts as it has been sitting for a long time. Jeep started right up. Turned on the high beams, blower motor to high and the electric fan and it held a steady 14.4 to 14.5 volts the entire time.

Put the old battery back in and nothing.

The battery is 3 years old. As i recently found out, the vehicle has had a bad alternator since I have owned it. So the battery has been drained 3 to 4 times just from the alternator draining it. Also, the alternator would not charge well at idle so it had a rough life there. Back in september when the Jeep took a swim, I had to drive the Jeep until the battery died and get a tow. When I got said alternator working temporarily, it died again and Iended up killing the battery twice driving with no alternator.

So I think 3 yearso f a bad alternator, dieing many times and getting contamination from the Jeep going for a swim killed it.

I am going to buy a new battery and see what happens.
 
Originally Posted By: cat843
One of the best batteries for the money is the Walmart MAXX. Many are made by JCI.


We have a JCI distribution center locally and they sell unlabeled batteries for $40. 1 year warranty
 
high voltage reading is usually not a battery issue, since the alternator is the only item capable of generating over 14 volts, and that is at the behest of the ecu. However, the battery could be damaged.

Alternator output is controlled by the ECU. if the voltage went high, the ECU is not sending the proper feed to the alternator-- this could happen if power to the ecu is weak and it is over compensating, or same if there is bad ground to the ecu (more likely). so when you look at connections, it's not battery connections you are concerned with as much but every ground you can find, maybe run some of your own to tie frame, ecu, engine, battery together.

the rest of your issues sound like weak battery, especially the weak starting. the battery may be weak from poor connections and poor charging.

flickering is not uncommon with chryslers. I had 1 that stopped that after adding extra grounding. another was reduced with a new battery but never completed gone.
 
14v is not high for a 12v system when the engine is running, 14.4v is the top spec. And if the battery is shorted it will not read 12v when in open circuit.

What does the battery read when fully charged, lights on, engine off?

I agree to check your cables. And some times the brushes will stick win the alternator when they get worn down or the slip rings is worn.

http://www.alternator-parts.com/
 
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