looks like I'll be getting an alternator

tulsaBill

Went to drive my car to a club meeting last night and had to jump start it. Went to O'rilieys and their tester said the alternator was making less than 30amps at idle. I've got a charger on the bat for now but it looks like i'll be swapping out the alternator this weekend.

I'm torn between keeping the car original with an OE replacement (complete w/ GT label) or rebuilding the original or upgrading to the 3gen 130amp model. BTW, does anyone know what the OE unit produces in amps when new?

So what if anything has anyone else done for charging?

92LX

I believe stock is 75 Amp. Every one has to do "their own thing" but when mine go's out I will stay stock.It's been good for about 18/19 years why change now!

tulsaBill

I found a doc that shows that the OE unit only makes 25amps at idle by design 75 a max. So when the tester showed less than 30amps that what it is suposed to do. I think I'll find somepleace else that can give me an accurate mesure of output rather than just < 30. If it's making the designed 25amps then I won't worry about it.

I'll see how things run once the bat is back up to a full charge and go from there.

tulsaBill

Turns out I don't think I need one anyway. When the car did not start I fiddled with the lights and what not to see if the bat was totally dead. I jumped the car and got it started and then realized that the map lights were on. I'm not sure if I turned them on when I was fiddling so they may have been on for a few days and killed the bat. I also disconnected my hood light 'cause I don't trust that mercury switch.

Anyway after putting a full charge on the bat I get 14.5v at idle w/ no accessories running and 12.9 with everything running. I think I'm good for now.

Today is one of our last nice days before the arctic air moves in so I'm rolling in the LX today. Just turned 31000 miles this week.

Stangfan

I did the same thing a couple of years back...played with the lights and didn't realize that I had left the map lights on. Came back a couple of days later to a dead battery.

kechme93

From my understanding, if you disconnect the POSITIVE cable from the battery and the engine dies, it usually indicates a BAD alternator.

tulsaBill

I would not recommend disconnecting the cable while the car is running. That method works fine on older cars but disconnecting the bat while the engine is running on a new car can fry the ECU.

The trouble I ran into comes from the test gear. Most in car alternator testers (like they have at Oriley's or Auto Zone) do not give you the actual alternator output stated in amps but only tell you if the alternator is making less then 30 amps. Since our cars are designed to only make 25amps at idle a modern tester will flag the alternator as bad when in fact it is working as designed.

kechme93

Installed a new alternator today on the Feature.

VibrantChick

Since we are on the subject:

Is it normal for your headlights and dash lights to be dimmer at idle
and then when your RPMs go up the headlights and dash lights get noticeably brighter?

This is how my Feature does, I want to make sure this is normal,
or do I need to think about an alternator?

Also, I have an Optima Red Top battery with 1000 CA and I think 800 CCA

tulsaBill

It's not normal for the lights to dim at idle but it could be any number of things.

To test get a good voltmeter that you can plug into your cigarette lighter and do some testing. Do all of this with the lights, ac, radio all off:

Start the engine and let it get past it's warm up cycle and see how many volts you are getting at idle.

Then take it for a drive and see how many you are getting at various RPMS.

After a run around town let it get back to idel in the driveway and see what you get.


Then repeat these test with all of your accessories on; bright lights, AC, radio, ect

If at idle you are dropping below 12v then you are draining your battery. It takes 12v to run the engine and various electrical components and any volts in excess of 12 are used to charge the battery. If your lights are dimming it's because the alternator is having to share it's limited energy with the engine and the lights leaving nothing left over for the batterty to charge so extra energy is drained from the bat to run the lights.

My car with a fully charged battery, new belt, and original alternator is making between 13 and 13.5 volts at idle with all the accessory on.

It could be as simple as a loose belt or worn belt tensioner. It could be bad cables, or it could be a worn alternator. If you do the test and you are getting less then 12v at idle then goto a good shop and have them run a battery and alternator test. Ask if their tester can show exactly how many volts and amps your alternator is making. My experience with Orily's and Auto Zone is that their in car test rig only give a green or red indicator on in car amps. In my case the tester showed red on the amps because the car was producing less than 30. But remember that by design our alternator only makes 25 amps at idle so to get a good test you need the actual number not just a red or green from the tester. If you are so inclned you can remove the alternator and have it tested out of the car and get a better reading. If the alternator is making plenty of amps out of the car then it points to something else.

If it's been a while since you changed your belt do that first. It's cheap and good insurance. See it that helps. If not then dig deeper. Check the cables that go from the alternator to the battery. Check the belt tensioner. Check your idle quality if it's poor you may need a tune up.

Your car was in the shop for quite a while wasn't it? You may just need to put the bat on a charger for a while.

hope this helps.

92LX

If you or someone has ever installed under drive pulleys ( for more power) that will happen even if every thing is good.

VibrantChick

I did install under drive pulleys.
Maybe that's it then?

She always starts up without a problem ;-)

Thank you guys for the input

92LX

That is exactly what happened when I installed underdrive pulleys on my 63 Falcon (5.0) and my 94-95 Mustangs. Voltage drop at idle, lights at night would dim and voltage gauge would drop , every thing would be fine when I went back to driving. Always started well. Just have to live with the problem at idle.