Hey guys thanks for answer my call for help.


I have a problem and im not sure what it is so i will describe it:

When all the lights are on (execpt high beam) and i press the brakes, all the lights dim down. When i let go of the brakes everything comes back to normal.

When all the lights are on (execpt high beam) and i press the brakes, my engine speed goes down. When i let go of the brakes the engine speed comes back to normal.

They both happen at the same time


Coincidence? I think not.

Any solutions anyone? and once again, Thanks for the help!

 

The lights dimming is caused by a crappy alternator. If it's not putting out enough power, the lights dim (and other stuff suffers) because they're forced to run off battery.

Check the output of your alternator per the FSM instructions. Or, for quick reference, is it putting out at least 13.4v?

As for the engine speed... not sure.

 

Actually, the alternater is about a year old, so its pretty new. And yea the car voltage is more than 13.4ish

 

Age doesn't really matter. It can still be bad. Less likely... but still possible.

Engine running, headlights & heater fan on high:
Alternator post to alternator frame = 13.5-14 volts steady (verifies the alternator output)
Alternator post to battery (+) = 0 volts (verifies the primary + wire)
Alternator frame to battery (-) = 0 volts (verifies the primary ground)
Turn off the motor, but leave the lights on.
Battery (+) to battery (-) = ~12.5 volts and holds steady. (verifies battery)

 

hmm.. alrighty so i guess ill get a mulit meter and do this?

 

Yeah. Shouldn't take more than 5 minutes.

If you don't own a multimeter, go buy one. It's the 2nd best tool we can own. 1st is a rubber mallet to beat **** with when we get frustrated (preferably nothing on the car... stray cat maybe...).

 

could some bad wires be the culprit?

 

Yeah. Messed up wiring can cause electrical wiring. Look for melted spots, corrosion, etc.

 

No, poor voltage is the culprit

If at any point the voltage is under 13.5 volts, you no longer have enough juice coming from the alt to charge the battery.

And if it is dropping under 12.6 volts... well at that point you are running on your battery.

At idle with a good condition alternator and battery, the voltage should be 14.4 volts. Foot on the brake or not.

Factory alt even on a S4 put out enough power to run an unmoddified car with all the lights (including brake lights) on and the engine running.

Now poor voltage could be caused by poor grounding of the battery, or of the engine, but that is about it, as far as what wiring can cause if the plugs for the alty are tight.

 

Can't bad wiring cause poor voltage problems?

 

Well in the case of a corroded to failure ground wire, yes.

But lets face it that is pretty damm unlikely.

The alternator is really only three wires, so bad wiring is so unlikely it should not even be considered.

You have the feed, the ouput, and the run signals coming and going from an alternator.

Of those three, you can throw away the run signal, because it only tells of complete alternator failure and has nothing to do with actual output of the alt.

So now you have a feed wire and the main output wire. The main output wire is a 6 AWG wire, so the odds of it failing between the alt and underhood fuse box is pretty minimal.

So the only other thing you have is the feed wire which the regulator in the alt monitors the voltage of the car with. If the voltage is above 12.6 volts, you know the feed wire is working.

So the only thing then left is a main ground to the engine, and you can pretty much rule that out if the car cranks.

So , no... no wiring issues based on his description

 

Ok, so it's possible, but very unlikely. Thanks for the clarification. I'm still working on this whole electrical thing-a-ma-bob.

 

oh.. soo how can i fix my prob?

oh and thanks you guys for answer my questions

 

oh and the voltage drops when i turn on the fan on hi

 

again, what is your voltmeter reading?

Sounds like your alternator is failing, but without knowing the voltage no one can say for sure

 

on average its above the 12, well above and when its hot it gets way above the the 12 but still i have the problem

 

I don't think you understood the question.

What is the voltage?

It needs to be above 13.5 volts just to charge the battery and should be at 14.4 volts.

 

it could also be the battery. if the battery isnt in good condition, it wouldn't be able to "absorb" the initial current draw before the voltage regulator picks up the voltage. In essence, the battery actually works in the electrical system like a capacitor does in a sound system.

I may have explained it kinda strange, but im doing the best i can. Someone correct me if i'm wrong.

 

Not on a S4. S4 models reference the regulator to the power wires for the ignition, so the regulator cranks up output right away.

He has a 86 Sport listed in his profile.

S5 and S6 models could have what you described though.

 

its hard to tell what the voltage is because everytime i press the brakes or let the idle go a little to low or turn the fan on, the voltage keeps going lower. and also my voltmeter is at around 14.4 area when im on the freeway for a while with lights of and around 13.5 when im on the freeway for a while with the lights on. so im not really to sure how to give you an exact voltage reading, sorry =( i hope this description helps

 

sounds like the alt is starting to fail or the alt is too small.

With normal lighting load, running at freeway speeds, you should be at 14.4 volts (just above the 14 volt tick on the guage.)

You mention fan. There is not an electrical fan on a FC that is switchable. If you have added an aftermarket fan, chances are the draw of it is unsuitible for the stock FC alternator. Most electric fans cans draw up to 20 or 30 amps, a borderline additiional load for a stock alternator.

and a electric fan should not even be on, at freeway (50 MPH+) speeds


.

 

oh i ment the inside fan, like the heater and a/c and stuff like that

 

ah, you meant the blower

 

yea, mm.. so is it the alternator that is weak? can i change the pully to produce more juice? can it be the grounding wire to cause these problems?

oh and one additional observation: The voltage gauge is moves around fron 12 to 14.4 a lot. It is usually 12 when the weather is cold (night) and 14.4 when the weather is hot (daytime) but it is not limited to that schedule. The voltage just keeps moving around but nonetheless, the light still dims and the engine speed goes down when i press the brakes whether the voltage is at 12 or 14.4

 

oh and i forgot to add:

Would a grounding unit be any good for my situation?

(Sorry for the multiple posts. I just forgot to mention this in the previous post)