wierd loss of battery charging

[Kiwi]

Hey fella's:

I have a stock standard 1997 TJ.  I went thru the big puddle in the gravel pit at McLean Creek too fast and had water coming over the hood (a little bit).  On the drive home after this experience I noted that the battery charging guage suddenly dropped to zero.  The jeep was running fine so I kept going. 

I let it dry out for a few days and then tried it again.  No problem starting, drives good, the battery charging guage shows about 11-12 volts (not 14v at the mid-point of the guage) but after 3-4 minutes the guage drops to zero.  I checked all of the fuses under the hood and they seem OK.  I took it to the pressure wash down the street and cleaned out the engine bay especially around the alternator.  After this wash the same sequence occurred.  Good start, good drive, battery charging guage at 11v, then after 3-4 minutes the battery charging guage drops to zero.

I guess the good news is that the guage works and that the jeep has spark. 

Anyone have any ideas what is going on?  Any ideas how to trouble shoot this error?

Cheers,  Kiwi 

[Immortal]

Welcome to my world.

Altenator. Wash the snot out of it. Keep an eye out for a new (or used) one.

[i_go_commando]

put a didital voltmeter on it and verify its not a guage problem. also pull aprt and conections in the charging circuit clean and put back to gether with some dialectric grease in the conectors. check your conections on the batteries and the alternator as well as body and chassi ground. also remove the baterie and clean up under the batteriy. most vehicles have a temp sender to tell the alternator to slow down the charging if the batt gets to hot. check your belts. disconect the belt and spin the alternator by had, and ugly noise or hard to turn is bad. failing that go find a alternator shop and get them to check. theyll know how to test and check everything.

basicly if your jeep is still running and the batteriy still has juice, the my guess its a gauge problem over a charging problem. EFI would kill your batt prettty quick with no charging. week charging my guess though.
any lights on the dash?

[Kiwi]

   Thanks for the advice!

I completed some cursory tests of the system with the following results: 
1. The alternator is only putting out 11-12 Volts according to a volt-meter.
2. The dash guage is correct at this time.
3.  After a short drive the dash guage drops to 9volts (bottom of dash guage) however the alternator continues to put out 11-12 Volts.

I'm not sure what this means.  Why does the dash guage drop?  I think I will get a new alternator...

Cheers,  Kiwi.

[TJ54]

been there, done that

New alternator should be the remedy, you should be seeing closer to 14 v with the voltmeter  and revving the engine a little

[i_go_commando]

pul apart and clean the conections. there is a definat problem there. may be a cheep fix