Battery or Alternator

[SR77]

When I come to a stop in my 96 explorer with a few things on like the heater, Headlights & radio, the rpms will drop down to 500 or alittle less and the Volt gauge will drop into the lower half of the gauge and all the lights will dim like its about to stall. Then after a few seconds the rpms will kick back up and the volt gauge will return to the normal position. Is this a sign that my battery needs to be replaced or is it a sign that there is a problem with my alternator? I would like to get this fixed before the winter hits so I am not stranded one day when it does finally stall out and I am hoping it just needs a new battery. thanks for the help.

 

[FreeWheelin4x4]

Got a voltmeter or multimeter? Measure the voltage at the battery, with truck off and a loaded battery (key on, AC on, lights, etc) see how far they drop, if less than 11.5V change battery.

Then try with car running and a load on (to duplicate your issue), if voltage is lower than 11.5V might be alternator also.

truck running should produce 12-14V at the battery due to charging and conditioning. Truck off, it should show 11.5-13.5V at the battery due to not charging and being battery only.

 

[budwich]

This is a sign your idle speed it too low and probably has nothing to do with your alternator or battery although you are seeing the effect (ie. low voltage). I would think that your idle should be a little higher. Check your IAC and MAF.

 

[410Fortune]

idle should be 800 RPM, 500 is too low.

Check voltage at battery duting idle as stated above, I like to see 14.4V with no accessories on. This indicates a perfectly working alternator and voltage regualtor (built in to alternator)

If the battery wont hold over 11.8V or so after being charged it is likely bad.

Any auto parts store can test both battery and alternator in or out of the vehicle.

the Low idle could indeed be a symptom of not enough voltage.
Does the low idle occur when you are not loading up the electrical system with all that stuff (headlights, heater, stereo, etc)?

 

[96limitedX]

i'm sorta in the same boat..

i now have a optima red top(not even a year old) and my truck used to dim and have the volt meter drop down alot. now with the optima i can have the heater on full,headlights/fogs wipers and it doesnt move. but if my ARC compresser kicks in or the rear defroster is on. it will drop alittle. my truck also idles at about 600rpms when stoped and warm. its fine when its cold and it idles at 1k rpms.

i would like to get rid of this alltogether tho..bigger alt? dual batterys?

BTW i have a load tester and i have tested the batt(new optima) and its very good. and the charaging system. the tester says they both are on the very high end of good. so what can be done about the moving volt meter/diming?

 

[SR77]

thanks for the replys. I don't think it is a problem with the IAC or idle speed because it only drops down to 500 or so for a few seconds when i come to a stop and then it will kick itself back up. Also this only happens when there is some load like the heater, radio and headlights on, etc. Doesn't happen when nothing is running. I am hopeing is just the battery going but wasn't sure. The battery I have now is about 5 or 6 years old. thanks again

 

[blast7]

Go to autozone and they can test your battery.

 

[96limitedX]

BTW this might help...check your battery cables at both ends. i just checked mine and i will be replacing my neg one hopfully tomarrow that should fix it(rubber is pulled back at the end where it bolts to the starter and i can see its corroded)

 

[xmodster3o3]

I have the same problems, i'm going to first replace my battery as it is kinda old more than 5 years old to be exact. If that doesnt work I'm going to replace the IAC. i'll post my results.