lights get dark when at idle

[zeusmoto]

hey guys i know that mustang alternators have never been very good and i was wondering if you can tell if one it about to go out on you. it seems that if i ever rev my engine for my friends or whatever it makes it so that when i am sitting at a light at idle, my gauges go darker and the car seems to lose some power. but when the light goes green and i give it some gas everything gets brighter and looks normal. soi was wondering what kind of alternator i should get next cause i guess mine might be about to go out.

 

[HyPer-50]

Yup, either your idle is too low or your alternater isn't putting out enough charge. May want to have your alternater checked. Do you happen to have a sub or amp or anything else that would be draining charge more than usual?

 

[zeusmoto]

nope just my massive engine

 

[zeusmoto]

oh yeah and how do you test an alternator also what would be a good solution

 

[NeQX]

it is your underdrive pulleys, either upgrade alternator or put on stock pulleys if it bothers you that much.

 

[Mustang5L5]

It's the underdrives.

Either put the smaller stock alt pulley on or buy the ASP 1 7/8" Overdrive pulley from summit ($20).

The smaller pulley will speed your alt up more so you can get better charge. If it doesn't work then, you'll need to go back to stock pulleys.

I have a 130AMP '95 GT mustang and still had the same prob. Alts need to spin to make power. I put the ASP pulley on with my underdrives and it fixed the prob

 

[zeusmoto]

hey also i dont have my ac in my car anymore that would take away one pulley right? so that would make the alternator give less power right?
so basically what you guys are telling me is that it is normal and my alternator is probably ok, you dont think there is a problem with it?

 

[Mustang5L5]

Having A/C or not isn't going to make a difference with belt speed.

It's not normal, but it's common. Like i said, it's because the U/D pulleys slow down the belt speed at idle. To compensate, put a smaller pulley on the Alt.

 

[zeusmoto]

so you guys think its my u/d's and not my alternator. i was alos thinking of putting a system in my car and i was wonder if the extra needed power would harm anything or would it make my alternator give out more charge? any ideas?

 

[87'GTstang]

Alternators today have variable outputs. Just because you have a 130 amp alternator doesn't mean it will put out the full 130 amps all the time (or the quoted 80 amps at idle). The more demand you put on them, the more they will give out - so in other words, relate that to your system to come, but not until you ditch the U/D pulley and then check you alternator. But even then, you 130 alternator should still put out the same if not more amps at idle than the stock 75 amp 2G alternator.......but I guess go for the O/D pulley first to see if it cures the problem.

 

[HISSIN50]

people sometimes still have low idle output (dimming lights and all) even after the 3G upgrade, so a pulley would be nice for now, as well as possibly nice for use later (if the shafts are the same size)....

 

[zeusmoto]

alright so sometimes it seems like the lights are right at idle and at other times after i gun it or rev it the lights dim at idle, is that still the u/d's and are all you guys asking my to get rid of the u/d's i thought they were good for your car

 

[Michael Yount]

zeus - don't guess at it; take it to Sears, PepBoys, AutoZone - they'll all load test the alternator and battery for you for free; that'll tell you if you have a charging system problem or not. Like others, I suspect it's just that your underdrives have slowed the alternator down to the point at idle where it can't keep up with the electrical demands.