Hi guys, I recently replaced my alternator on my 90 l98 and the person I brought it to said he replaced it with a "rebuilt factory original". It's been running fine up until a few days ago when I sat in the car with it running for a while with the heat on and noticed the voltage was @ 16 and dropping off to 13 or so and then going back up again. Also sitting at a stoplight today with my headlights and right blinker on the voltage would go up and down with every blink and also when I step on the brakes. Can anyone help identify the problem. Sorry if it's completely obvious and a stupid question. I am assuming it's the alternator. Thanks a lot guys.

 

Just take it to Autozone. they will run a free charging system diagnostic in 5 minutes with the car running.
That way there will be no guessing what the problem is...

 

Uhhh, I'd love to except I live in minot ND and we don't have those great fancy stores I used to have the pleasure of going to in NH...we have a checkers and they will only read trouble codes for free, so does any else have any suggestions on how I can diagnose this problem? I can always take the alt back out and bring it back but I'd rather not unless I have to.

 

16 volts is still within GM's allowable voltage, but its a bit abnormal. The more common output is 14.3 volts (on the dash voltmeter) when the alternator is cold and this will drop to 13.3 volts hot. If your alternator isn't charging the battery the red battery symbol light will come on on the dash. The voltage regulator attempts to maintain constant voltage across the battery but it cannot react instantly to sudden loads like turn signals flashing or brake lights turned on. If the load stays on, like keeping the brake depressed, the voltage regulator will drop and then recover to its normal charging voltage. I don't think you have anything to worry about unless the alternator doesn't charge the battery or if the voltage goes over 16 volts.

 

Ok, thanks alot. Yeah the voltage is usally around 16 all the time, seems higher than what it used to be and it does keep the battery charged though. I just thinks somethings up with the "rebuilt" one I got back. I think it may be incorrect for my car since the alternator bracket and air pump to alt bridge thing didn't line up right. Oh-well, I guess I'll have to wait til I can get a high output one made for my vette in the future. Thanks again.

 

Any auto service or garage can check that for you. It should not cost much!

 

You better have it repaired fast. 16 Volts in a healthy battery means a whole lot of charging current what may result in problems. First is may toast your dynamo. Second (out of experience, depending upon the type of battery), Acid may boil out of the battery. I had that with an other car and found out too late because the lights went bright sometimes. The acid had boiled out and entered the chassis beam. Half a year later I could dump the car because it did rot away. Ours are fiber, but acid still can do a lot of damage at cables and parts. Reason was a bad regulator. (for our generators it costs approx 10$ and is easy to change.)

 

you should double check the charging over 16. it will fry other componets. been there. i would say check grounds around the bay but if your 16 or over expect other replacments......

 

I'll look into the regulator...may sound stupid but haven't heard of that til now. Hence why I'm here right? To learn more each day. THanks a lot guys. Oh yeah, any tips for replacing regulator? All I have is a haynes manual tucked away somewhere in the garage, so I'll look in there when get a chance.

 

Have you checked the charging voltage at the battery with a good meter?

 

Take the generator out and place the front part in the vice. Remove the 4 nuts and pull the halves apart. The carbon brushes will click out of the holders, no problem.
The regulator is the white plastic box where the brushes are connected to. You need to take the nuts off the connections to the diode bridge That is the 3 connection block where the wire from the coil run to. Than take the brass connection off those screws that hold the regulator , remove the other screws that hold the regulator and remove it. Take care not to loose washers and put the washers at the same place they came from. Mount the new regulator the same way you took the old one off.. Now push the carbon brushes into the holders and put a 2 mm pin through the hole in front of the brushes. The pin should come out of the back of the case. That holds the brushes into place while you mount the two halves together. When mounted, pull the pin out and click, the brushes are back where they belong.
Take care to clean the copper sliprings with very, very fine sandpaper before you assemble. Do this while turning the rotor so the paper marks are in line with the movement of the rotor. Otherwise the carbons will have a shorter life.
Good luck

 

How Is Your Battery? Had A Bad One On My Other Car. It Didnt Have A Ampmeter Like Our Vettes, But The Lights Would Dim Ea Time The Turn Signal Flashed Or When The Air Condidtioning Came On. Had It Checked At Sears. Alternator Perfect, Battery Gone.

 

Nico has given you some very good advice. The only thing I'd differ on is using the sandpaper on the slip rings. If they look clean and smooth, I'd suggest you clean them with clean paper towels and Isopropyl alcohol instead. If they won't clean up this way, then some extremely fine grit sandpaper may help, but I'd save this for the last resort.

16 volts may be within spec, but as a constant condition it's not good for your battery, and it may shorten the life of other electrical components as well. It suggests to me that your regulator is not working optimally, and may be preparing to fail completely. I'd replace it.

A straightened-out paper clip works very well to retain the brushes in their housing while you re-assemble the alternator casing. As Nico said, you can pull the paper clip out when the case is assembled, and the brushes will snap back against the slip rings.

Be well,

SJW

 

IMO it sounds like the Battery is on its way out more than the alternator. I've been through this, and if it is infact your battery, then if you don't replace it, it will in turn ruin your alternator. I had a weak battery in my old '86 I had. I finally replaced the battery after having to get jumped a 2 days in a row. Then the alternator went within a week because I had been over working it to keep the other battery going as long as I could (broke college student at the time). And I know it was the battery first because I had it tested and it came back only able to hold about 10 volts or so. I had a good mechanic friend thats been doing it for many years and said he sees this all the time. He also told me it works the opposite way as well, if the alternator is going out and not charging, it will put undo stress on the battery, and if not fixed, will cause a dead cell in the battery.

 

Thanks for all the advise guys. I appreciate it alot. That's why I love this forum!