Alternator Charging Issue

[Original Trailster]

Yesterday was the first time I drove long distance with this problem. About an hour after the gauge died I lost power to my radio and instument lights, about half hour after that the engine died. It seemed to me that the battery was not being charged and everything ran until the battery was depleted. After sitting for half hour the engine cranked right up with a problem, I let it idle for 15 minutes to get some charge back in the battery then the guage died a few minutes after I started to drive again.

My alt gauge shows as working when I first start my jeep then within a few miles the gauge goes dead. If I turn the ignition off then back on it works again for a few moments then quits. It will idle in the driveway with no problems but most of the time quits soon after I start driving. My battery is new and this issue was present with the old battery so that should not be the issue. I have had my alternator tested 3 times in the last six weeks by different parts stores and it seems to run perfectly. I have cleaned the connections and tightened everything. This is a 2000 wrangler and I believe the original alt. Any suggestions on what to check or replace?

I am still suspecting the alternator but I read about one issue with kinda simular syptoms where the ignition switch was the problem. I'm just totally confused and do not want to buy an alternator if it is not the issue.

 

[SteelHeadz]

Possiblly a faulty battery temp sensor.
A battery temperature sensor, located in the battery tray housing, is used to sense battery temperature. This temperature data, along with data from monitored line voltage, is used by the PCM to vary the battery charging rate. This is done by cycling the ground path to control the strength of the rotor magnetic field. The PCM then compensates and regulates generator current output accordingly.

 

[Original Trailster]

I found that the ecu sends 5v to the sensor so I can test for that. Anyone know how to test the sensor?

 

[Sid1966]

I had intermitent charging problems on 97 tj.on my jeep it was brushes,easiest ones i ever done,you dont even have to split the case.while trying to find problem noticed voltage changes from 13.2v to 14.8 vwith battery sensor hooked up when unhooked stayed at steady 13.5v

 

[Sine Deviance]

If the alternator tests good and the system still isn't charging, the PCM could be shot. The voltage regulator is on the PCM and they do go out. This causes your alternator to not kick in.

It's just another possibility. I just had to replace my PCM because of this same problem.

 

[TJExtreme]

I saw some PCM on ebay last week for $25.

 

[SteelHeadz]

The voltage should vary between 5V to 0 volts.
The BTS is used to determine the battery temperature and control battery charging rate. This temperature data, along with data from monitored line voltage, is used by the PCM to vary the battery charging rate. System voltage will be higher at colder temperatures and is gradually reduced at warmer temperatures.
The PCM sends 5 volts to the sensor and is grounded through the sensor return line. As temperature increases, resistance in the sensor decreases and the detection voltage at the PCM increases.

 

[jfrabat]

The voltage should vary between 5V to 0 volts.
The BTS is used to determine the battery temperature and control battery charging rate. This temperature data, along with data from monitored line voltage, is used by the PCM to vary the battery charging rate. System voltage will be higher at colder temperatures and is gradually reduced at warmer temperatures.
The PCM sends 5 volts to the sensor and is grounded through the sensor return line. As temperature increases, resistance in the sensor decreases and the detection voltage at the PCM increases.

Is this a TJ thing, or does it apply to YJ's as well? I dont remember any sensors on my tray... By the way, I am asking to expand my own knowledge, not because of the original post.

I saw some PCM on ebay last week for $25.

I saw one like this for mine and bought it as a spare, as ECU's can be VERY expensive, and they tend not to be on eBay when you blow yours (for some strange reason!). I would pick up one if I were you...

 

[Sid1966]

start it drive it until the gauge shows discharge leave running getly tap back of alternator check your gauge.if tapping alternator makes it charge it is probably brushes,that means a new alternator or put brushes in yours.it onnly took me about 40 minutes to pull alternator change brushes and reinstall.

 

[Sid1966]

if it is a nippon denso you only have to pull cover plate on back of alternator the brushes are right there no need to split the case

 

[SteelHeadz]

Is this a TJ thing, or does it apply to YJ's as well? I dont remember any sensors on my tray... By the way, I am asking to expand my own knowledge, not because of the original post.



I saw one like this for mine and bought it as a spare, as ECU's can be VERY expensive, and they tend not to be on eBay when you blow yours (for some strange reason!). I would pick up one if I were you...

I don't remember when this BTS was first introduced in the Jeep family, i doubt that the technology was that advanced with the YJ. I know for sure that they are commonly found on the WK, some XJ's, KK, Jk, TJ and the rest of the Chrysler product line that's equipped with the J-tech PCM's and newer.

 

[Original Trailster]

The BTS tested ok so I went ahead and put a new alt in this afternoon since it is cheaper than a PCU and I could get one right away. Everything seems to run fine now. I ran about 15 miles without an issue. Weird how the alt kept testing fine. If I have any more issues indicating that the alt didn't fix the problem then I will post up.

I thank all of you for your input.