alternator?

[kyle2blue]

Hey again,

I have another question. When ever I turn on my lights at night, more so when i do it with the fog lights on at the same time, my idle drops for a split second. could this be a sign of alternator going bad. battery is only about a year old. I do have a stereo system that's about 800w. but even with the stereo off it does it too. any ideas?

[Pirate_copy]

Have you checked your Alternator belt is not too slack buddy?

[kyle2blue]

we just changed the belt yesterday when I changed my water pump, tstat and housing.

[Pirate_copy]

Any grinding when you first start the car? maybe a bearing is on the way out in the alternator

[kyle2blue]

no grinding. it starts up pretty quick.

[Pirate_copy]

Well unless your battery isn't charging properly, i am out of ideas mate

You are loosing juice somewhere :(

[fun2drive]

Measure the voltage at the battery with the engine at a fast idle like over 1600 rpms, 2000 is better. Allow the engine to run at this rpm setting for a while before you measure the voltage. The voltage regulator gradually ramps up and it will take a little while say around a minute to be up to max voltage. You should see a max of 14. 5 V and a min of like 13.2 V. Allow the engine to idle and see what you get. Anything below 12.5 V is a strong indicator of a voltage regulator going bad. Remember for your car there are 2 different regulators depending upon the manufacturer. I think on is Bosch and the other Valeo.
Pull the alternator to replace the regulator which is bolted to the back of the alternator.

If voltage is good then either you have too many appliances running or most likely a diode is shot thus requiring a new or reman alternator...

[Conehead]

Could just be the extra load put on the electrical system by the lights.

I wouldnt worry about it to much, unless the car starts stalling

Cone
xxx

[BMWredneck]

If voltage is good then either you have too many appliances running or most likely a diode is shot thus requiring a new or reman alternator...

hahahaha we are talking about a car not a kitchen!:rofl:

[Bimrpwr]

I am with Cone. When turing on headlights and fogs it will drain a little power from the battery/alt. My alt is fine and battery is fine and i it will do it to me as well. Even when the A/C turns on. My radio is always checking the volts on the car and i can watch that move down a couple of numbers when this happens and then goes right back up

[jason_recliner]

Here's what's going on.

Battery voltage sits at point X.
When you start your lights, particularly halogens which have a higher surge current, the battery voltage drops slightly. The more lights at the one time, the larger the drop.
Your voltage regulator notices your battery at X minus a few volts and switches in the alternator to make electricity.
The Alternator requires more turning force (torque) to generate electricity.
This increased physical load drops your RPM until the engine management kicks in a little more throttle to stabilise the RPM. It may still even sit lower than it did with lights out.
Once the lights are up to operating temperature (say 200ms ???), they also draw about half the current they did at the switch on instant.

It's actually a sign that everything is good. If your alternator was bad, you would not get the same RPM drop.
It's also reasonable that your RPM can increase for a short time when you reduce a heavy electrical load, such as turning a lot of lights out.