RedScoob

Every now and again, I'm experiencing what I think is a voltage fluctuation problem in my car (a MY95 WRX). The headlights will dim and brighten (cycling between the two around every two seconds) for a few miles and then they will return to normal. When this is happenning, the hot air fan slows down and speeds up, and the instrumentation lighting dims and brightens aswell.
The connection to the battery is fine, and the battery never looses charge. I'm thinking that it could be the alternator, but is there any way to make sure before replacing it on a hunch? Also, if it was the voltage regulator, would the symptoms be the same?

scoobian

it sounds like theres an additional load coming into play, to me
is there anything else switched on in the car which only operates occasionally?
...something 'automatic' perhaps?
try and work out under what circumstances you get the dip (turning/braking/night/day/accelerating etc etc

scoobyboy

aircon maybe?

RedScoob

Thanks. The aircon is switched off and the fan set to manual, I can't think of anything else that could operate occasionally (radio off, etc.).
I'm praying it's not the alarm as I have no idea how the wiring works for that and I can imagine it would be a nightmare trying to locate an intermittent fault of this nature.

mit

iTrader: (10)

Im having the exact same problem!
It's not the aircon, or engine fan (happens 1 min after starting with no reading yet on the gauge), not the radio as it's off.
I was thinking about the voltage reg on the alternator too, as if it was faulty, then the output would be AC, not DC.
Can these be changed?

Mit

tanyatriangles

iTrader: (2)

I'd get my alternator checked out by an auto-electrician sooner rather than later

mit

iTrader: (10)

Trouble is it's an intermitent fault, so unless it is playing up when tested, you won't see a fault. I've found a new one for £85 + post, does this sound right?

Mit

RedScoob

Maybe worth putting a voltmeter in the glovebox, then measuring the battery terminals when the problem occurs? I don't know if that will actually tell me much though, the voltage is bound to go up and down.
mit, I take it you don't experience a flat battery or any other symptoms?
The only other symptom that I experience is that very occasionally the car will crank over but not fire, but I think that is alarm/ immobiliser related (and only happens once every 3 months or so). Resetting the alarm cures it.

mit

iTrader: (10)

No problems, other than the battery light has flashed once. The revs do drop at idle when it happens.

mit

iTrader: (10)

Well im soon to find out if the alternator fix's it as i've just ordered one! I'll keep you posted.

RedScoob

Good luck!!!
My plan of action is to check the earth straps (once I find them!), check the fuel pump connector under the rear seat (I've heard they can short out - I know, a bit of a long shot!), check all the fuse box connections and wait for the next time it does it...... I'm tempted to take it to an auto electrician as tanyatriangles suggested, but with it being such an intermittent fault I don't think the problem would show itself.
Let me know if swapping the alternator out cures it for you.

mit

iTrader: (10)

Wait a couple of days, i should get it monday. An auto electrician could cost the price of an alternator!

STI_Baly

iTrader: (23)

Sounds like the alternator is on its way out to me....same issues with a focus i repaired 2 weeks ago....abs light and traction control light on due to voltage dropping below 6V, battery light came on and it all died eventually.

But First if the headlights brighten or the blower motor picks up speed when you rev the engine you may have a weak battery this indicates the battery may not be holding enough current to run the car and is working off the alternator. (get the meter out again)

Good Luck

mit

iTrader: (10)

Right an update.....
I fitted the new alternator a couple days back, and it's cured the problem! The car feels better, idles better, and the lights are not pulsing anymore!
Also, it's all shiny, and looks smart!

Mit

adzer

iTrader: (13)

yip i also had this problem, you could hear the idle of my engine change and the volt gauge i have fitted would drop from 14v to 10v then bounch back up.

i tought i had a loose earth or summit but never looked as car run fine then it just lost all power and died, fitted a spare altenator i had and fitted it and hey presto the car was sorted and felt faster than ever before

RedScoob

Thanks mit, I have ordered a new alternator. I hope it sorts the problem as it did for you.
Merry Christmas everyone!

RedScoob

Sorry for the huge delay, ordered the alternator and didn't have time to fit it until last week.
The result is that the car runs smoother, the lights don't pulse anymore and I'm no-longer hitting fuel cut!!! Result!
Thanks to everyone who offered advice!!

mit

iTrader: (10)

Glad you've sorted it, mines still fault free!