99 E300D Battery Light
 

Hello,

I am trying to figure something out on my Mom's car...I searched the archives but could not find anything.

This morning as she drove the battery light came on and the engine almost seems to have what sounds like a miss-fire following this light coming on.

I hooked a meter and find voltage is low, suggesting the system is not charging. My bigger concern is, as I described, what sounds like the engine is mis-firing.

I know there are many more electronics on this engine than older ones, and my experience is all with older diesels. I'd like to get it to a shop, but I am afraid of driving it with the low/no charge and doing some damage to the engine or injection system. Back in the days of yore, the battery was mainly for starting unless you needed lights, but this is a different animal, and I don't want to make a costly mistake.

I would sincerely appreciate any advice.

Thanks, Tony

What voltage are you getting at the underhood battery connection when the engine is running?

If you have a Bosch alternator you can remove the voltage regulator/slip-ring brushes from it quite easily as they come out as a unit. See if your brushes are worn beyond their serviceable length. Phil has them for $31.00.

How many miles on the car?

Hi, Thanks for replying. The car has "only" 185,000miles on it so we are outraged the original alternator seems to have failed so early!! :D

When the car is running it is at 12.0volts or slightly less.

Unfortunately I will be out of town and can't take care of it myself (and looking at position of alternator...not sure if I want to!), but was worried about driving the car anywhere to get someone to take care of it for me. As I wrote, it almost seems to have a miss-fire. Back in the olden days, I once rescued a stranded friend by taking the battery of out of my old VW diesel while it was running, and put it in his gas engine car so we could get it home. The diesel car drove normally the whole way...just no radio! Now, the diesels have a whole different level of electronic needs, and I was trying to find if driving it with low or no charge can cause engine damage.

Thanks again for your help.

How old is the battery? I find it hard to believe that it would still have the original battery in it, but if it does throw it away and get a new one.

Len

You should be getting over 13 volts if the alternator's doing its job.

Try this:

DISCONNECT the battery under the seat and THEN connect a charger to it. If it accepts a full charge, reconnect it and see how it drives. You may be able then to get it to someone to fix it for you before it totally dies.

That misfiring noise is normal, when you have low voltage. Its probably your battery, you can check alternator voltage on the climate control by pressing "ec" for a long period of time. I get high 13's that is normal I guess.

pull out the black plastic piece on the back of the altenator (voltage regulator-2 screws- if the 2 springy bars are worn that is your $25 problem) car should get over 13.5-14.02 volts with a good alt/voltage reg.

if your battery is over 4-5 years this could be it, but pull the volatge reg to be sure.