Searching4Sierra

iTrader: (27)

On my way home today the car was running fine but then all the lights in the cluster started to go on and off. The radio faded in and out along with the headlights.

When i got home i could not start the car again, it just clicked.

is the battery dead, or the alternator?

the connections on the battery look good

NBM-LS1

iTrader: (7)

jump the car.

If it dies right away its probably the alt.

If it stays running Its probably the battery.

You can check the output of the alt with a volt meter. If its putting out 13-14.5v it may be ok. That does not mean the diodes in the bridge are good though.

Also it wouldnt be bad to have the battery checked.

How old is that battery? I dont think LA gets cold enough to make a difference?

Does all the other stuff turn on in the car?
Turn the headlights on. Note how bright they are, then jump a good known battery too it. Do they get brighter?

98TAjwh

iTrader: (4)

i had a similar problem. all the indicator lights started coming on and such. turned out to be the alternator.

chaman

iTrader: (5)

When the gauges go crazy like that most of the times is the alternator. Charge it up and have it checked if in doubt with your local Autozone or PepBoys.

Searching4Sierra

iTrader: (27)

i know how to check the battery, but how would i go about checking the alt.

btw i have no idea how old the battery is, it was in the car since i got it 2.5 yrs ago from NJ

thanks for the input

chaman

iTrader: (5)

One thing I do is with a voltmeter and car at idle measure how much charge (in terms of voltage) battery is receiving. Increase RPMs and again see if the volts increase accordingly. It should climb up to 14V or 14.5V...at idle it can go from 11.5 to 12.5...thats aprox. GM states that a idle voltage of 11.1 (in F-bodies) is acceptable although I feel a bit uncomfortable with it.

tom falco

NEVER NEVER NEVER NEVER NEVER NEVER NEVER NEVER EVER DO THIS. The battery controls voltage spikes and if you do this it will be your worst nightmare. Check the voltage at 1100 RPM'S it should be between 13.5-14.7 depending on battery state of charge. At idle with a meadium load it should never drop below 13.1V. Have the battery load tested at the parts store. You can also have the alt tested as well. Once again NEVER DISCONNECT A BATTERY WHEN A CAR IS RUNNING.

chaman

iTrader: (5)

Bad info...not ever attempt it. That applies to older cars but not to the complex and powerful systems modern cars have....Scratch this post.

chaman

iTrader: (5)

Agree....the values of 11.5-11.1 are with a FULL load according to GM...thats all lights running, AC, stereo...the whole thing.

Jeff Smith

iTrader: (44)

Agree..Never disconnect battery whhen motor on running..

horsepower_junkie

iTrader: (4)

Alright guys my bad... I knew better than that I just had a brain fart. I've played with old small blocks that you could do that with WAY too long. A voltage spike would fry some stuff in a hurry if you unhooked the battery on that thing running. Words of wisdom: DON'T POST STUFF WHEN YOU'RE HAMMERED!!!! Once again my bad guys... Im really not an idiot... Just used to the old school stuff.

chaman

iTrader: (5)

LOL!! Dont sweat it man....thats why boards like these are great for leraning new things. I learn new crap here almost everyday!

02v8ta

iTrader: (8)

we don't disconnect the positive cable from a battery why exactly? it'll fry the newer computer systems? is that right?
i just did this to my friends (1999?) dodge to see if his battery was dead or the alt. but i learned that trick from autoshop. my teacher was an "old timer"

tom falco

That spes is the maximum output of the designed alt capacity. For some reason GM gives that number and it is useless. AT that voltage you are running on battery power and discharging the system. All in car voltage readings must be higher than 12.9V. Example police cruisers and ambulances would conk out when the voltage goes below 10.9. If left to idle at 11-12V you are discharging the battery. I have a contract with the local town and we service all the municipal vehicles. If a police car is at an accident or with the light bar on and all the other accessories it would eventually kill the battery. If left that way for an extended period of time with a low voltage output It will conk OUT. It will also set a code in the ECM . (LOW ALT OUTPUT). The old theory of disconnecting the battery to test a ( GENERATOR ) is a holdover from the old days. Alternators are EXTERNALLY EXCITED and will go nuts without a voltage reference from the battery. Remember an alternator has a VOLTAGE REGULATOR not a current regulator. Generators have both voltage and current regulation. Remember you need .2 volts for each cell over voltage to keep the battery charged and healthy . 12 volt batterys have 6 cells so the charge rate should never be under 13.2 V. Modern batterys have memory. If they are always undercharged they will never be able to be at there full capacity. Never undercharge a a battery. Especially GEL CELLS. (OPTIMA ETC) Hope this explains this. Nice discussion guys thats what its all about. Peace TOM

toadzq8

iTrader: (43)

Guages going nuts, no radio means you have a low voltage problem.

tom falco

Totally Correct.

Z28/2002

iTrader: (27)

my car was doing this last week and I swapped the battery and it hasn't happened since

Searching4Sierra

iTrader: (27)

thanks for the help. it was the alternator....that solved this problem

chaman

iTrader: (5)

Thats great but watch out for the alternator...if it is going it will take the battery with him.

chaman

iTrader: (5)