[MBZ] My adventure of driving a OM642 powered vehicle with a dead alternator

[Kaleb C. Striplin via Mercedes]

So as I posted yesterday we went over to Branson MO for the weekend 
intending on returning late this afternoon.  After spending a few hours 
at Silver Dollar City we then headed to the hotel.  When I parked it I 
noticed a strange smell that was sort of a mix between hot brake pads 
and hot electrical.  With the stop and go traffic and the hills over 
there I did not think much of it.  Later in the day around 5pm on the 
way to dinner before a show the red battery message came on.  Crap.  So 
we get to where we were going and I check everything and I still smell 
that smell but nothing under the hood seems amiss.  After the show gets 
out around 9:30 I go out to the car and get the display up with the 
voltage reading.  It showed right at 12 volts.  I start the car up.  It 
drops but then comes back to about 11.9 while running.  I thought the 
wife was on the way but 15-20 minutes later while the car is sitting 
there running further draining the battery she shows up.  By this point 
it was down to 11.8 or so.  We head across town with the headlights on 
as it is dark.  We get back to the hotel and the voltage is at about 
11.6-11.7.  I shut it off.  So this morning we get ready to leave the 
hotel and voltage was about the same but the darn thing started right 
up.  Ok, so I located the nearest FLAPS and spent $189 plus core on a 
AGM battery and bought a HF type socket set for $40, all of this in case 
I had swap the battery out.  If it dies half way home I figured I could 
pop the new battery in and continue on my way.  The battery is located 
under the passenger seat in the R class, like it was in my former GL but 
in the GL I could get it out by moving the seat all the way forward.  On 
this car the seat has to basically be removed.  In prep for not being 
able to move the seats forward or backward with a dead battery I moved 
it all the way back to remove the front 2 bolts, then moved it all the 
way forward and left it that way in case worse came to worse.  So we are 
on our way.  Car jumped voltage up to 12-12.2 for a couple of brief 
moments but for the the most part ran in the mid 11s the first part of 
the trip.  When the air suspension pump kicked on it dropped the voltage 
for a few minutes.  I probably should have just pulled the relay for the 
pump so save power.  After a while we were dropped to around 10.8-10.9.  
About 8 miles from home we were at the low end of the 10 range and the 
suspension pump kicked in and dropped the voltage below 10, at that 
point the ABS and traction control systems went offline. After the pump 
kicked off the voltage came back up and those warnings went off.  Got 
about 3 miles from the house and it starts sprinkling.  I was worried I 
was going to run into a rain shower well before we got home which would 
have really screwed us. About this time the voltage drops to about 8.9 
and further systems shut off, the transmission starts downshifting, and 
the fuel system seems like it starts shutting down as the car was losing 
power for a minute.  It did this a few more times but we got it all the 
way home.  I pulled in the driveway to unload the car real quick before 
pulling it into the shop.  By this time the transmission was now in limp 
mode as it only had 1 gear and moved very slow across the yard to the 
shop.  So, I can tell you for certain with minimum power usage you can 
drive a 642 powered vehicle about 2.5 to 2.75 hours or about 180 miles 
with a dead alternator.

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