Could my bad alternator cause this too??

[ran1078]

O.k I've been having problems withe my voltage. When I drive the battery is between quarter abd half way but when I stop my voltage drops to almost nothing. Talked to a mechanic and he said go home with the car running unhook the neg. on the battery and if the car shuts off its your alt. Is he right?? And this problems been driving me crazy and costing me alot of money too. The problem is when I come to a stop if I don't have my air cond. on my car shuts off!! If its on its o.k. plus when I come to a stop my rpms bounce up and down from a quarter way to 1 up and down. Now does this have to do with a bad alt. or why does it do this?? Please help cause I had enough of reving it up at stops or the damn thing sometimes stalls even with the air on. HELP ME HELP ME PLEASE. THANKS

[ran1078]

no one can help me??

[NickR]

Disconnecting the battery with the engine running, and seeing if it stalls, is one common way of testing whether the alternator is working. But I have heard some people say it can cause damage to do this. A safer, and more accurate method, is to buy a multimeter (say about $20 or $30 for a cheap one) and test the voltage across the battery terminals with the engine running. It should be 14+ volts. But I can't think why your mechanic didn't try this. It only takes 2 minutes, and every mechanic would have a multimeter.

When you turn on the AC, it automatically raises the idle rpm of your car, so the alternator spins faster, and produces more power. I cannot tell whether your idle problems are caused by a bad alternator. It might be something else.

But the low voltage is probably caused by a bad alternator. Other possible causes are dirty battery terminals (disconnect them, and clean them with sandpaper, then reconnect them) or a bad battery (can be tested with the multimeter- 12+ volts with engine off -- or tested for free by most battery shops).

Best thing to do is to clean your battery terminals, then buy or borrow a multimeter.

[crazyman]

disconnect the battery while engine is running - you are asking for trouble. any car with a computer, this should never be done. this was a good test for the cars without computers back in the day. nowadays, when the battery is disconnected and reconnected while the engine is idling, there is a voltage spike that can go as high as 50,000 Volts, and it doesnt take very much to fry any electrical circuit. proper way is to get an AVR test done, or just get a multimeter and check the voltage across the battery terminals. if it still isnt charging, check the wiring on the alternator also.

[94KYGt]

well first off they are right about the multimeter, it is a safer way to do it. Also, the battery cable test is for the positive terminal not the negative. The car will stall every time if you do the neg. The point of the pullling the terminal is to make sure the car is not running off the battery. If the alternator is not working then there will be no current going to the car when the pos is removed. If it is working the car will still run fine. I have never heard of any problems from removing the terminal while the car is running.
Steve

[96GTZE]

also if you have a vac leak on the air conditioning... it will cause your car to stall used to happen all the time on my ze

[ran1078]

also if you have a vac leak on the air conditioning... it will cause your car to stall used to happen all the time on my ze

Thanks for the advice but my car stays on at stops only when the air is on. I have no vac leaks on my air. Back to my question which I don't beleive was answred here. Everytime I go to start my car its dead. I have an optima red top batt I got in June. When I drive my voltage is close to halfway but when the car is at a stop idlinging its reading on low in the red. Does this seem to you guys that my charging system/alt. is not charging my battery? Thanks

[PGT96AJT]

is the idle set too low? this might cause the alternator to not spin fast enough. it would also cause the air conditioning to not blow as cold.
also when you turn on the AC the idle speeds up to compensate for the extra lag so the higher idle might be high enough for it not to stall.