Dimming lights, HVAC Motor slowing with lower RPMs

[BlackSunshine]

Hey Guys,

So I have noticed somehting that I don't believe existed prior to installing some underdrive pulleys. This could be coincidence but I'd like some feedback. I've noticed now that when my car is idling and I blip the throttle the headlights and dome lights (if they are on) with brighten up a bit when the RPM increases and when it settles back to idle, they will dim a bit again. Also, the heater/AC motor will increase in speed and the decrease when the RPM's settle back to idle.

My question is if this behaviour is a product of slowing down the accessory system by the UDP's or could this be and issue with the alternator/battery? I have logged my charging system through my X3 and it will show 14+ volts until the car is warmed up and then settle down to 13.5-6 but the fluctuation in the values are not really affected by RPM speed, maybe .2-3 volts. In the old days this was usually a sign of a bad regulator or what not and I'm not even sure if these cars use an external voltage regulator to be honest.

Note that I am still on the original alternator and battery from 2005. Thoughts?

Cheers.

 

[JeremyH]

Sounds like an alternator issue.

 

[BlackSunshine]

Sounds like an alternator issue.

Any idea how accurate the voltage readings are through the OBDII port?

 

[JeremyH]

Nah, I always measure voltage at the battery while off vice running. Should see 14-15 volts while idling.

 

[skwerl]

I'd suggest a 130 amp PA alternator from American Muscle. They have a great reputation and a lifetime warranty, and AM is a great vendor that will back up any product they sell.

 

[BlackSunshine]

Nah, I always measure voltage at the battery while off vice running. Should see 14-15 volts while idling.

As would I if I had access to a volt meter. Through the X3 it seems ok, 14+ while idling and slowly drops after quite a while. It is my understanding that the PCM on these cars also regulates the voltage requested so I am thinking that the small drop (half a volt or so) is probably normal. I'm also wondering if the battery might be causing this. I think it's on its way out, already 7 years old.

I'd suggest a 130 amp PA alternator from American Muscle. They have a great reputation and a lifetime warranty, and AM is a great vendor that will back up any product they sell.

Trying to avoid an unnecessary expense at this point. Don't want to just throw parts at it if its not required. Thanks for the recomendation though.

 

[BlackSunshine]

Anyone else have similar behaviour and know what the cause was?

 

[08stang]

notice my head lights were dimming at idle while parked or if i came up to a light a couple weeks ago checked things out like you did everything seemed ok alternator shit its self last night and from what i can tell took the old battery with it as it no longer will hold a charge, got a new battery test drove the car and the juice was sucked right out of it so im pulling the alt at daylight. my you should at the very least have the retards at the local autozone test your alternator

 

[JeremyH]

$5 at walmart for basic votlmeter. Read the battery after the cars been off for 24 hours if its under 11 volts its time for a new battery.

 

[QWIKFIX]

I have that issue only when I turn on the rear widow defogger along with headlights and heater. Honestly to me its the udp's

 

[skwerl]

Batteries are not as bulletproof as some people think. If the alternator is going then you might as well replace the battery at the same time, otherwise you'll be replacing it after it dies on you a couple weeks later. Batteries simply won't continue to hold an adequate charge after they have been discharged to the point of failure.