whos up for a challange?

[allbentup]

So i have an 88 sami other than tires, rims a header and msd coil it is totally stock Its my daily driver got to love that 25mpg. My wife was driving it around one day and it died on her. I was at work in a meeting and she couldnt get me on the phone, so she took it to local shop. they diagnosed it with a bad alt and dead batterie. So they put in new. a week later the same thing happened, still under warranty they put another alt and batterie in at no charge. Well that lasted for about 6 weeks now the same thing is happening. So, i wanted to diagnose it myself here is what i came up with: i first did the old school check on the alt, ya know disconnect the batterie while it is running. and it did run so alt is good. then check the output voltage of the alt. it is putting out 16 volts with no load on it (not connected to the batterie) but once connected to the batterie it only puts out 12.58 with no accesories turned on and 12.89 with heater on full, lights on high beam. That doesnt sound right to me. i thought it sould be in the 14volt range so one question that i have is where does the alt get its signal on how much to charge,correct me if im wrong. but i think the voltage regulator which is internal on sami alts does this. second question what are the 2 wires on back of alt? I took the car to a local diagnostic shop and told them what is going on. they hooked it up to a machine that checks the charging system and they gave me a print out saying that the charging system works just fine. So i drove it in this morning and by the time i made it to work i almost could not see my dash lights. when i checked the volts on the batt i was 10 volts im at a loss W.T.F. any suggestions are greatly appriciated thanks in advance.....

[purevil71]

have you checked ALL of your grounds? Samurai's are VERY picky about there ground wires. Mine was doing something close to this, and I had a bad ground wire.

One runs to your Alt light on your dash, not 100% sure what the other one does....lol

[bildo]

then check the output voltage of the alt. it is putting out 16 volts with no load on it (not connected to the batterie) but once connected to the batterie it only puts out 12.58 with no accesories turned on and 12.89 with heater on full, lights on high beam. That doesnt sound right to me.


You're correct, you should be reading something close to 14 volts or more at the battery while the engine is running. Given the information that you have provided I would guess that you have a wiring problem. I had a similar problem years ago where one of my alternator wires had worn through the plastic insulation because it was rubbing on something. A bench test of the alternator and battery showed that both were good however I still had a charging problem. Once I found and replaced the bad section of wire, the charging problem went away.

[allbentup]

i checked all the grounds and even ran a new wire from batt to fuse box....problem still there so well see i have a couple ideas to try this weekend. i had old dodge like 10 years ago that had similiar problem cant remember what it was though................................
i will post results on monday....thanks purevil71 and bildo for your suggestions.................later.....

[allbentup]

so i found 2 things 1 there was a problem with the orbital battery that i bought from 4wp it was shorted internaly only once i got warm. the 2 thing was a short in the starter silanoid when warm also replaced both and it seems to be ok.... there is 14 v at the batt when running...so i guess it is ok..the crazy part about this is that i had 2 bad brand new batteries so my point is just cause it is new dont rule it out, check it any ways then rule it out.

[simonw]

Its not a really common problem to have a battery thats shorted internally. Does the voltage rise when the RPMs are brought up? On newer vehicles you should never take the cable off the battery to check the alternator. It can not only burn up diodes in the alternator, but can also damage your ECM if you have one. Check your grounds. You should run anywhere from approx. 13.5-14.5 Volts at the battery. if the voltage is low... like 12.5 at idle... and it increases to the normal range with higher RPMs under no load... then the diodes in the rectifier are bad (alternator is bad). Make sure all your battery cables are in good shape. Good luck.