bad alternator ?

[wishbone83]

I have a 96 Cherokee Sport, inline six 4x4.
I think i may have a bad alternator but i am not sure. i just replaced the battery about 9 months ago and and it seems like the truck is having a hard time maintaining a charge. now i barely drive it but i start it at least once a week if not twice and have never had any problems untill last week. i had to jump start it with my company car (07 taurus) to get it running.... after doing that the only way i could get it to start or stay running was to give the jeep some throttle. and if i took my foot off of the gas (or braker bar) the jeep would stall allmost instantly, and than would not have enough juice to restart. if i would get it running and turn evrything on, i would get flickering lights. so what i really want to know is if anyone knows what reading i should get if i thrwo my multi meter on the alternator too see if it is pusing out the right voltage and aperage. i have a real nice multimeter that i use at work (hvac-r service work). id rather test it my self than take it off and go to autozone with it just to find that there was no problem. and if anyone else thinks they know what the problem is let me know.... last year i had a problem like this and i had to replace the batt.... my dumb ass lost the recipt and im hopeing i dont have to buy a new one.

[MagicRat]

Test the battery voltage with the engine off. It should read about 12 volts, when it has a good charge. It sounds like your battery may be discharged so it may read a bit less.

Then test the battery with the engine running. The voltage must read between 13.7 to 14.5 volts. Any less means the battery is not being charged. Any more means the battery is being overcharged and will eventually fail.

If it does read within the acceptable range, try turning on some electrical accessories (lights, rear window defog etc) , rev the engine a bit and see if the alternator can maintain voltage under load.

[Scrapper]

sounds like alt or something draing it you never left no lights on did you. first thingy you can try is to unplug his alt and just jump start using battery on his car it then you will know witch one it is leave yours pluged in. just see if it works and shut it off because you'll be running on his battery.

[fredjacksonsan]

You may also want to check your positive battery cable; I've had vehicles that had corrosion in the cable about 6-8" in, and that killed the whole car.

[Scrapper]

reson why your pos cable gets build up is your alt is putting to many amps than the battery can handle.

[gtmud]

Its your alternator! Just to double check, get the battery fully charged and checked. put it back in the truck and start it, with everything on, your volt reading at the batttery should be about 13 volts. Let the truck run a while and watch the voltage, if it steadily drops below 12 volts @ idle with load, then you alternator is toast. Get one from Napa or auto zone, NOT from advance, unless you want to replace it agian soon.

[gtmud]

WHo told you that!? (too many amps to the battery) Do you realize that there is no possible way an alternator could over power a battery.( Battery is at average about 540 CCA, Alternator out put at about 70- 90 amps) Over charge maybe, but there would be other issues.

[Scrapper]

when i worked at shied we had a battery meeting with interstate battery the guys in suits said it was a myth that you couldn't charge battery on cement. then i ask a question about the pos side of battery caroading up he said good queston then he said the battery cant carry the amps that the alt was putting out. so really it boils down to the battery not having enough cca or you got to big of alt.