After a year of chasing down why the battery will not stay charged on my son's 850 wagon I have reached the conclusion that either the alternator or voltage regulator needs to be replaced. A month ago I parked the car with a fully charged battery and took a reading last week (engine off) it read 12.64 V. That is down from 12.70 when it was parked. Not too bad.

I drove it to work twice and took another reading; now 12.30VObviously, the alternator is not keeping up.

My questions are can the voltage regulator be replaced? With the alt still in the car? Or does it make more sense to just replace the whole alternator? How big a job is that? The belt is nice and tight so it is unlikely that it is slipping although the front bolt through the alt bracket is missing??

Thanks for your help!

Tim Benner
Centerville, OH

 

voltage reg is/was available from fcpgroton, I new alt wouldn't hurt

 

I would take the alternator out and have it tested at your local Napa or other auto parts store that can test it. If it is not staying charged, I would strongly suspect the alternator. The main function of the regulator is to keep the alternator from OVERcharging the battery

 

Thanks guys. Now that you put it that way it makes perfect sense. I'll pull the alt and take it to be tested. Probably pick a new battery up too. This one (A-zone) is 8 months old. With a pre-charge reading of 12.3v, the charger indicates 100% charge after 5 minutes and the battery reads 12.95V. After 10 minutes off the charger it reads 12.5v. Something about that is just not right.

Thanks again,

Tim

 

Hmmmm. I would still check the alternator just to eliminate it, but it could be that the battery had a faulty cell in it.

 

I agree to all the above. Voltage reg is expensive, and it is better just to replace thealt with a rebuilt Bosch with lifetime warranty (Pep-boys has them).

Also, I would check for parasitic current draw. One time I had the same problem and was narrowed down to the glove box lamp. I got rid of the bulb and the problem never came back.

The replacement is not too bad, but there is one bolt that is hidden and you kind of have to feel it. Also, other components (idler pulley for the serp. belt, PWS pump reservoir) have to be either moved out of the way or removed. But if you have a good set of socket tools the job is not too bad.

When you install a new alt, make darn sure that the battery is fully charged, or the voltage reg in the new alt may be damaged. As to batteries, stay away from franchise brands’ cheap products. I would go with The Interstate Batteries.

P.S: MikeySq, good to see you! It’s been quite a while and I am not sure if you remembered me but I sure did remember you! How’s the weather up there?


JPN

 

Thanks Psabioc and JPN. This car did have a parasitic drain... never found but it miraculously went away when I replaced the exhaust header. After replacing that it held a charge for a month, going only from 12.74 to 12.6.

Since the battery is losing voltage when disconnected and reports full to the battery charger within minutes it must be faulty. We'll start there.

All of the usual parts houses have the alternator so I'll take the plunge there also. The missing frontalternator mounting bolt indicates that someone before me may have started in that direction.

Thanks for your help!

Tim

 

Please let us know how it goes

 

I would do the easiest (cheapest) thing first. REPLACE HE BATTERY because if the battery is reporting fully charged to the charger in 5 minutes, it is doing the same to the alternator as well. Also from my past experience, the regulators on alternators short and result in overcharging instead of under-charging. If the generator part of the alternator go bad, then you will see the batery light comming ON on the dash.

So......My bet is on the battery first.
Good luck

 

Hi guys, do you have the electronic circuit for the car ?

Thanks,

 

I have a PDF of the wiring diagrams for the car, but it is 58 pages and 2.7 Mb so I can't attach it. I can send it to you by e-mail if you want