940 Battery/Charging System

stereomonostereo · Post by **stereomonostereo** » 29 Jun 2012, 11:24

Hey guys,

I just had my head gasket, timing belt and water pump replaced on my 1993 940. Everything seems to be as it should, but occassionally when at low RPM, all of the dash warning lights come on. I understand that means there's a problem with the charging system. After driving about 30 miles round trip, i checked the battery, which is dead on at 12VDC. My alternator belt looks good and seems to have the right tension. The car hasn't been performing any differently, and the lights are only coming on from time to time when my RPMs are below 1000. Anyone have any insight on where to go from here?

Thanks in advance!

Post by **jimmy57** » 29 Jun 2012, 12:11

A battery with 12V without key on and with interior lights off is not well charged. New battery full charge is 12.72 or a little more. below 12.5 in the same situation is not being charged or if charging system is working properly the battery is on its very last leg.
All of this testing would be 4 hours after engine is run or more to assure a higher voltage is not what is known as "surface charge".
Belt can be snug and still slip due to the rubber drying out and getting polished and having poor grip as a result. Slipping belts don't always screech.
Tighten the belt some more to see if that has any effect. Easy first step to figuring it out.

stereomonostereo · Post by **stereomonostereo** » 29 Jun 2012, 15:51

Well it's definitely the alternator. Now comes the task of finding a replacement.

Mine is a 100 amp, i believe it's the Nippon Denso unit. Does anyone know if a Bosch is interchangable?

stereomonostereo · Post by **stereomonostereo** » 03 Jul 2012, 15:10

I ordered a replacement alternator, but while waiting for it to arrive i installed a used one that a friend had. My service lights aren't coming on anymore, but i'm not getting the charge that i should. I did some light running around last night, but this morning when i went to start the car, the battery was drained. I stopped at the local auto parts store and had them test the battery and it tested good.

Next i did the recommended Chilton alternator test. With the car not running i'm getting 12.1 on the battery. Once started with no real electrical load and the engine at 1500rpm i'm getting 13.1. Once i turn on the fan and the high beams and rev the engine to 3000 it drops to 12.9.

I checked the alternator brushes, which seem to have some life left to them. I'm kind of wondering if it's the voltage regulator. The new replacement alternator from SwedishAutoParts is arriving on Thursday, but i'm just checking to see if there could be something else wrong in the charging system. From what i gather it's pretty much just the alternator with the internal regulator, and the battery. Any ideas?

Post by **jimmy57** » 03 Jul 2012, 16:29

I can't remember if that year has the alternator mounted with rubber bushings at all mount points or not. If it has the rubber bushings then there will be a ground wire. If it is broken it will not charge nor will all the warning lights come on when key is turned on before start. (see your other post)