kponti

Yes I know it has been beaten to death and I have read all there is to read on this matter and it doesn't solve my problem so any new ideas? I would hate to add to and raise another thread from years ago so here is a new one.

I recently had to replace both batteries and alternator (burning smell, left me on the side of the road) in the last week.
Batteries both tested and trickle charged to full.
Alternator tested several times out of car....Good
Replaced both batteries....Good
Replaced Aux relay...
Replaced voltage regulator again....should be good right?

All have left me with same problem. Occasionally the red battery comes on, and the convenience features turned off message comes on.
It usually goes off a few minutes later.
I can make it come on if I go wide open throttle

Any ideas??

biggking

Isn't there a battery regulator box in the trunk or something?

Critter

What are you showing for voltage, running should be as you know 14.2volts idling. With all accessories turned on, heater, defroster, AC anything that draws current from the battery, then check for 14.2V, slight increase in RPM maybe to hold the voltage at 14.2V, other than that possibly you have a diode issue inside of the alternator.
When you say the alternator was tested, what was the current output of the unit. Close to spec.
Does your car have a ground strap from the engine to the frame? Clean battery terminals with battery brush also cable connections cleaned.
MB Bosch regulator? or aftermarket piece?
Any more information?

kponti

When the car is being normal, the readings are always between 13.8-13.9 volts at idle and any other rpm no matter whats turned on. When the dumb lights come on, it drops to 12.1-12.4 and holds. As I drive, it will suddenly start climbing up and settle around 13.8/13.9 again and the lights go off
Current alternator was tested out of the car and within specs (I will look for sheet when I get home). I am going to have it tested inside car as well while running.
Don't know about the ground strap but if it not factory, then no I do not have it
Yes MB Bosch regulator from dealership
Yes cleaned out all connections

kponti

Yes the BCM, I am going to swap it out with another car and see but the odds of that being the issue is slim. I KNOW my alternator was bad before I changed it, When it went bad and I drove around on my battery power, that must have helped ruin the old stock batteries so I had no qualms changing all of those. I just do not want to repeat all the people who have changed all the charging stuff only to find out that none was the culprit

Critter

Normal operating voltage is 14.1- 14.2V.
I know 13.8 or 13.9V seems okay, but it is telling you that the alternator is not performing correctly.
The charging electrics are working good as the lights come on when the voltage drops off to the 12V area. You state you knew the alternator was bad, did you in fact change out for another alternator with a new regulator or just your old alt and a new regulator.
The only other point you may consider is the connection to the alternator from the car wiring, are these connectors clean and tight a loose alt plug may cause you issue, but personally I would look for another alt if those connections are tight.

chiromikey

I would point my finger at the BCM in the trunk. I had one go out years ago.

Critter

Can the BCM fail and then be okay soon after and then fail again?
12.1 12.2 is your battery power, with no alt assist.

kponti

Good point Critter, I will say 90-95% of the time, the voltage is 13.8-13.9v every once in a while does it drop off to 12-12.4v

kponti

I knew the alternator was bad when it started melting plastic and I replaced the whole thing (NAPA Bosch reman), then I replaced the regulator on the new alternator with ANOTHER MB one straight from the dealer, regulator. I then replaced the batteries both front and rear ones and charged the front one for 18 hours.
Now it wont run out of juice or die, it simply cuts off my accessories for 20-30 seconds at a time

That's what I am trying to determine before doing that painful job again. I had the alternator tested in 2 different places, both ran the tests 3 times each with successful results before I settled on that one.

So could it be the BCM? How coincidental that it goes out right when the alternator essentially catches fire

Or is it my new alternator with a diode problem? If so how did it pass 6 separate tests?

Can it be the auxiliary relay? Yes the battery light comes on but the low voltage message also comes on

kponti

A bit more info:

So I said it would cut out the accessories at idle and WOT. I also said it will drop the voltage to 12-12.4v. What I did not realize was the order at which this occurs

Actually when the accessories are cut out and the red battery light comes on, the voltage stays at 13.8/13.9v for a few seconds before dropping down to the 12s. So all of this is happening at normal voltages (well normal for this setup at this time), and the car's ecu compensation is what is dropping the voltages down to the 12s

Critter

Was the alt connector damaged when the first alt burned up?
I am still considering the alt is the issue unless you have damaged wiring.
With the car off turn the key to the on position and then turn all the accessories on including the headlights, check the voltage it will be in the low 12's or even high 11's, now start the car, immediately the voltage should jump up to near 14V. If not then the alt/regulator are not working properly. Just because it worked on the Napa test bench does not mean it will function in a Benz, seen many issues with just using non bosch parts so who knows just what is used inside of a reman from them.
What is the voltage of the front battery when car is not running.

kponti

I will recheck voltage of the front when not running and report later tonight. It was very low (brand new just put in the acid and didnt charge) when I first tested it, but I havent sinced I charged it.

Wiring is all good and yes it is in the low 12 when key is on, jumps up to high 13s when the car is started.

Yes I also wonder if the alternator could be the case, in that case I may have to shell $780 for a new alternator from dealer plus the $160 core charge (since NAPA has gotten rid of my core by now). If that's what needs to be done, I will gladly do it, I just want to be sure first.

Critter

Before doing anything else, CHARGE the front battery with a battery charger. The alternator is not a battery charger but more of a battery maintainer. This could be your issue as the charging system changes from the main battery charge to the front battery which is probably 10 volts if you are lucky.
Numerous short drives will not help with your issue.
Charge the battery!!


and not just for an hour preferably depending on the size of the charger overnight at a slow rate is better than a fast charge for a short time, you do not want to boil the acid from too much current.

kponti

I will charge again tonight (should get at least 10 hours of charge by tomorrow). However do not forget I already charged it for about 18 hours over the weekend

Yacht Master

If this info is true, 13.9 and can be pulled down to 12.1 it is one of two things, a super huge electrical load/short or a POS alternator.
Tell us more about burning smell, did you find out what burned up?

kponti

Yes burning was directly from the rear of stock alternator.

Bought NEW NAPA Bosch alternator, replaced new alternator's regulator with new one from MB dealership. Car is having symptoms as described above

Yacht Master

Ok then you need to get an idea of the load on your alt. most good shops have a meter that can measure the load and determine what is drawing excessive amperage, one thing for instance could be the AirMatic pump or relay getting ready to burn up or SBC it has a big motor too. I think you are only fixing the damage caused by a problem you have not found yet.
So smell around for other burnt electricals.

kponti

Of the two options we can safely eliminate the airmatic (I am on BC steel coilovers and the airmatic option has been turned off with STAR). The SBC was something feared too and since it is still under warranty, I had it checked out and passed (it was replaced a few years back anyway).
So I am guessing on to find a different power draw then

Critter

Yacht Master, if it was a high load or direct short the voltage would not stop at 12V do not forget there is a 800 cranking amp battery hooked directly to the alternator any shorting or excess loading the wiring would light up like a flare. I still believe the issue is either an alternator regulator loose connection( possibly effected by the heating on the previous alt) or issue within the alt. Could the op tell us why he changed the reg on a reman alt.
The 12.1 or 12.2 the op is reading is the battery voltage without the alternator adding more voltage to get it to 14.1V
When the new alt was put in the car were the batteries disconnected from the car.
Also now what is the aux battery voltage when resting, 12.6-12.8V?

kponti

yes the Aux is usually at 12.8/12.9v at rest. I replaced the alternator after which I replaced the regulator with a new regulator. The melting issue is NOT on any of the new stuff, any part associated with the burning has been discarded.

I did an experiment last night. WOT about 4 or 5 times in a row shifting close to 6000rpm in 3rd. I did it close to home with the intention that whatever is broken should simply break completely so I can replace the right part. The car never got back above 12.1v after my runs no matter how long I cruised afterwards. The main battery checked out at 12.2v and the aux checked out at 12.6v when I got back home. So in this case, i feel the alternator never got back online.
I placed a trickle charger on the main overnight, same voltage reading on the main this morning. However with much colder weather, the car started back up at 13.5/13.6 volts and stayed there till I got to work.

I am thinking Critter may be right, my new reman alternator has issues keeping up with the power demand on the car

Critter

You state the main was the same voltage in the morning after trickle charge, what was that voltage?
Tell us why you changed out the reg from the reman and put in an OEM Bosch, what were the symptoms prior to the new regulator being put in the car. Was there issue with the reman alternator from the start as purchased?

kponti

Main was 12.2 in the morning

I changed out the regulator because the car left me on the side of the road dead after putting in a new (reman) alternator. So I changed out the regulator again (wasn't sure if the regulator was at fault) and changed out the two batteries to new ones.
So the alternator seemed like it was cutting in and out when I first put it on. After batteries and regulator change, I have not been left on the roadside since, but I am still getting messages like above

N_Jay

12.2 is too low for a good battery after being on a good charger overnight.


The battery is bad, the charger is no good (or way too small) or you have a parasitic drain.

Critter

Njay is correct, either you have a bad cell in the new battery or your charger is not working properly, maybe bad or dirty post or charger clip. Reinstall the charger and check with your volt meter after about ten minutes you should see and increase in the voltage, if starting at 12.2 which is telling you the battery is only about 65-70% charged or down on a cell. When you charge it this time disconnect the main at the neg terminal so it is independent to the car. then recheck for a voltage increase when the charger is connected for a few hours. One point is some chargers have smart technology and will not charge a bad battery (shorted or bad cell)


Still thinking alternator is crap but also maybe you have a bad main battery, we need to separate the issues as you now have two, the alt or the batt or both. If you had the old main battery I would be putting that back in after a good charge, just to verify and negate one issue.