is it the alternator

[hutch]

the past 2 days the battery charge on my truck has been reading lower and lower. my dad told me to test the alternator by starting the truck then pulling off the positive terminal from the battery. he said if the truck died then it is the alternator. i tried it and the truck did die immediately. is this a valid test? is there anything else i should check before replacing the alternator? the battery was just replaced a few months ago so it should still be good.

 

[KELLY88]

If you can make it then take the truck to Advance Auto or Auto Zone and they can test your alternator in the parking lot. If it's bad they'll let you know right there whether or not it needs replaced. Or if you can't make it then pull the alternator and catch a ride, they can bench test as well.

 

[hutch]

sweet thanks! i'll give it a shot.

 

[almostclueless]

God, I wish that hillbilly testing method would die.


Anyone who removes a battery cable while the engine is running stands a good chance of killing the alternator, regulator, or both.

 

[hutch]

good to know. now i can make my dad feel stupid! haha but i looked under the hood and noticed the alternator pulley isn't moving so thats where im statrting.

 

[Bob Ayers]

Not only can you kill the alternator & regulator, you can kill the PCM, GEM, anything electronic powered by the battery!! NEVER remove a battery terminal when the engine is running!!!

 

[shadetree]

The problem in removing the battery cable with the truck running is if the regulator in the alternator is no longer regulating, when you disconnect from the battery, it can allow the alternator to go to full amperage output, and burn up a lot of stuff. If the alternator is dead, as it apparently is in your case, the truck simply dies same as turning off the ignition key when you remove the battery cable.

Next time, invest in a $5 Radio Shack volt meter, and check voltages.shady

 

[hutch]

thanks for all the advice guys. it does seem that its just the pulley on the alternator. i got it spinning again and the truck was running fine but it keeps catching every once in a while. any advice on keepin it from stopping?

 

[shadetree]

The pulley on most alternators has a key in a slot on the shaft to keep the pulley from slipping. If the nut holding the pulley has come loose, it could have damaged the pulley,or allowed the key to fall out/break, or simply needs to be tightened up.shady

 

[Bob Ayers]

The problem in removing the battery cable with the truck running is if the regulator in the alternator is no longer regulating, when you disconnect from the battery, it can allow the alternator to go to full amperage output, and burn up a lot of stuff. If the alternator is dead, as it apparently is in your case, the truck simply dies same as turning off the ignition key when you remove the battery cable.

Next time, invest in a $5 Radio Shack volt meter, and check voltages.shady

It's the di/dt that creates the huge voltage spike when you remove a battery cable. This can happen just with the current load on the battery.
The load isn't sufficient, for the alternator to go "full amperage", but large voltage spikes will be created. The voltage output of the alternator
is controlled with the "voltage" regulator, not the current.

 

[StanDeSD]

Geez, Bob, I'm a bit rusty of my calculus. How about if I just take the integral of d2I/dt2 instead? In any case, that might explain why my 95 XL 2.3 has a terminal case of ammeter needle bounce. I continually have voltage regulator problems and need to replace the alternator every couple of years. Am I frying one of the diodes in the voltage regulator (I have a 95A integrated alternator/regulator...)?