97 TJ charging system isn't

BENG · 09-25-2008, 04:06 PM

1997 4cyl TJ (one of the first ones in '96 I might add) 186,000 miles

Original problem--about 6 months ago or more my volt gauge would start at its normal position, then go down to about 9 volts, then down to zero. Start it up again, the gauge reads fine. Intermittently the gauge goes to zero.

Pulled the alternator to bench test...it's good. Battery, good. Everything else working ok. So I write it off as a bad gauge and drive it.

This week, lights start to dim, radio goes out and Jeep starts sputtering. I get it to work and park for a few hours. Drive it to the local autoparts, test the battery, good. Load test battery...BAD. Charging system test...BAD, but I had searched on here and found out the alt needs a good battery to work properly. So I replace the battery. Check charging system again...BAD. But at least I can make it home on the new battery.

Remove alt for benchtest. Alt tests GOOD. Dang!

Checked all the fuses, both underhood and under dash...all good. Dang!

My guess is the computer is intermittently feeding a charge to the battery, then shutting it down. And for the past 6 months I have been running on battery only at times until the computer said to charge it...finally the battery bit the dust and couldn't run like that anymore.

Before I go with a new computer, am I missing anything? A hidden fusible link somewhere perhaps?

And if computer is my only option left, do I go $250 out the door for a new one or take a chance on used for 125...My way of thinking is any used one is going to be 12 years old and probably close to dying as well...thoughts?

Thanks for reading and thanks in advance for any ideas. I hate electrical probs!

**Jerry Bransford** · 09-25-2008, 05:14 PM

I'm a bit confused, what exactly is the problem you're having now since replacing the battery?

**Skyryder** · 09-25-2008, 05:46 PM

Not real sure what it sposta do, but there is a batt. temp sensor in/under the battery tray. This sposta "prevent" over charging, , hmm wonder it that do-dad went ti's up ?

I'm sure someone else here has more expertize with 'em

BENG · 09-25-2008, 06:36 PM

The problem now is that the battery is good, the alternator is good, but the charging test is still negative.

Basically charging system is dead according to the tester so I am just running on the battery.

And thinking back, until this week I really never drove that Jeep at night, so I wasn't drawing a lot of juice by using the lights, the intermittently charged battery was able to keep up with the minimal draw.

I should mention it also registered a 47 code on the odometer before the battery change, but is NOT showing a check engine light.

thanks

BENG · 09-25-2008, 07:06 PM

Hmmm...here is something from a post deep in the archives by rm2001wj: "While working on the the AC, fan relay, etc., did you ever unplug the PCM? I have heard of the connector making a poor (and intermittent) contact on one or more pins even if the harness has not been unplugged."

It's from a totally different problem, but the other code I forgot about besides 47 was 12--direct battery input to the PCM was disconnected within the last 50 key-on cycles.

I discounted that as some sort of glitch, but first thing a.m. I will play around with the PCM connector.

(and I notice my name doesn't say Jeep Forum supporter anymore, so I guess I better go and renew!)

**Jerry Bransford** · 09-25-2008, 07:10 PM

Quote:

Originally Posted by BENG

The problem now is that the battery is good, the alternator is good, but the charging test is still negative.

Basically charging system is dead according to the tester so I am just running on the battery.

If the battery is fully charged, the alternator will barely be outputting any power at all. It only puts out power when the battery needs charging but most of the time during the daytime when the lights are off, the alternator is doing little more than loafing.

BENG · 09-25-2008, 07:48 PM

That would be too simple...No problem at all.

But we tried loading it up with lights when we tested the charging system, and nothing. Wouldn't it show some kind of charging even with just the lights to tweak it?

BENG · 09-25-2008, 08:10 PM

Skyryder, thanks. I have been searching on the batt temp sensor...finding other tips along the way, but it doesn't sound like my problem.

Hopefully Jerry is right and I don't have a problem! And maybe my volt gauge really IS broken and not related to this charging thing at all.

The good news is I am a JeepForum supporter again...my renewal just went through!

Thanks again.