Charging System Problem

[az735i]

Just trying to confirm that the alternator on my 98 ls has died. Charging voltage with lights and ac on was at 9.8 at idle, went up to mid 13s at around 3000 rpm. The charge indicator comes on only when the voltage drops below 9.8. With the lights off, ac on voltage is at 11.5. The car has 124k miles, and no PS leaks. I replaced the PS pump last year, because it was noisy, but not leaking. The battery is OEM and a year old. I also got the VSC indicator yesterday while stopped at a light, which prompted me to check the charging system.

Voltage on my 735i was at 13.6 at the same conditions as above.

So this leads me to believe that the alternator has died.

[SRK]

Sounds like it has -- so remove it and have it repaired by a good automotive electrical shop, or diagnosed there. Probably just needs a set of brushes, if not a diode or two is blown.

[curiousB]

Yes Alternator definately not putting out enough power at lower RPMs. Do you have a PS leak as well? This fluid is known for damaging the brushes and causing early failure of alternator. If you have that leak you need to fix it too or you'll be doing the alternator again.

I'd bet its 99% the brushes. The fact it works some suggests the rotor is just being starved for field current so it under performs at low RPM. Its possible to replace brushed yourself if you are adventurous.

[az735i]

Thanks for confirming.

I would replace the brushes, I just don't have the time due to my work schedule, so I'll replace the alternator.

The car does not have a PS leak, though I saw that the pass. side valve cover gasket is starting to weep.