Starting Failures *URGENT HELP NEEDED!! - Page 3 - Mercedes-Benz Forum

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post #21 of 45 (permalink) Old 08-26-2004, 11:10 AM
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RE: Starting Failures *URGENT HELP NEEDED!!

for battery info
http://www.uuhome.de/william.darden/
the life span of an alternator depends on how the electrics are used, if you added a power booster radio with massive base speakers and had the air con on with your lights/heated rear window plus any other toys then it will be short lived because it would overload the system, if you had the car standard as when new but only drove it at night then also it would be loaded so as to the life span it is difficult to say, check the power supplied to the battery with all other things turned off they way you were testing the battery before with all the lights on will only determine if the battery is ok and the alternator is giving enough power, with every thing switched off you are testing the output of the alternator and at a guess i bet its higher than 15 volts and if it is then the alternator is suspect, good luck
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post #22 of 45 (permalink) Old 08-27-2004, 12:29 AM Thread Starter
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RE: Starting Failures *URGENT HELP NEEDED!!

If the charging of the alternator is insufficient or fluctuating, could it lead to an failure of starting the car via the ECU?

If yes, how come other functions such as the air con or lights does not dim out intermittently?

It seems that my alternator reading may be 12.5 - 12.6 Volts when the car is used used but my battery's capacity is 100V. Does it make sense?
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post #23 of 45 (permalink) Old 08-27-2004, 01:54 AM
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RE: Starting Failures *URGENT HELP NEEDED!!

Quote:
the_girl_i_love - 8/26/2004 7:18 AM

By the way, what is the life span of an alternator? My reading for the car’s electrical charging was 12.6 Volts
Why don't you get the charging system tested somewhere you can look over their shoulder and get all of the results, that really would be the most straight forward way to figure out the charging system components? Voltage, current, and which ones fall in spec and which fall out of spec.

A new alternator should last, on average, 7 to 10 years. A rebuilt alternator probably 5 years plus. The rebuilt usually cost much less. That's the way I would go if I needed to replace it. In either case, make sure you get a good warranty. While they should last that long, it is also possible to get one that will fail unusually early.

Without knowing what condition you measured the voltage under, anything conclusion would be a guess.

At the time you start your vehicle, it is the battery that matters most. But if there is a problem with the charging system, then yes, it could cause a starting problem that may or may not be have anything to do with the ECU.

Somewhere above you mentioned a pretty low current. Normally when the charging system is tested, it is under load. The measured current should be pretty close the current rating of the alternator. So, to answer the question, you need to know the specs on that alternator.

Quote:
It seems that my alternator reading may be 12.5 - 12.6 Volts when the car is used used but my battery's capacity is 100V. Does it make sense?
Is this when the car is running? Is it a fast idle or just regular idle? Battery capacity is normally expressed in ampere•hours. That number is not usually provided for car batteries. The number we usually see is cranking amps or cold cranking amps.

If you can't go and have the load test done, here are some things you can try with your dc voltmeter or multimeter set to dc volts.
First check all the belts and make sure they are not worn, cracked, or loose and are not slipping.

Turn off all of the accessories, with the engine running somewhere between 2000 to 2500 rpm (fast idle), measure the voltage across the battery. It should be in the 13.5 to 14.5 V range. If the voltage is below 13.5 V, then there is most likely something wrong with the alternator - definitely something is wrong somewhere if it is below 12 V. If the voltage is above 14.5 V, there is probably something wrong with the alternator (most likely the regulator).

If that went ok, now turn on everything in your car that will draw power - the headlights, radio, a/c, put the fans on high, dome lights, rear defroster. With the engine at a fast idle like the last test, measure the voltage. It should still be between 13.5 and 14.5 V. When you have the test done by a tech or at the dealer or auto supply, they do a load test or load pull instead of turning on all of the accessories.

If the voltage is low in either or both cases, also measure the voltage coming directly out of the alternator. If that voltage at the alternator is in the right range, the alternator should be ok and there is something wrong between the alternator and the battery (if the battery voltage is right, you still should have the battery tested at some point).

One more thing to test is the field voltage if you can find the wire. It might be marked with an F (I've never looked for it in an MB). That voltage should be right around 12 V.

Hope that helps a little. Good luck.
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post #24 of 45 (permalink) Old 08-27-2004, 08:21 AM Thread Starter
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RE: Starting Failures *URGENT HELP NEEDED!!

quote:
--------------------------------------------------------------------------------
It seems that my alternator reading may be 12.5 - 12.6 Volts when the car is used used but my battery's capacity is 100V. Does it make sense?

Is this when the car is running? Is it a fast idle or just regular idle?
--------------------------------------------------------------------------------

Thanks for the info SledDog,

The above readings 12.5 - 12.6 volts show when the with the engine running somewhere between 2000 to 2500 rpm.

So to conclude my alternator understandings;

My alternator may be working fine but it is not charging sufficient electricity to the ECU (if there are not faults) to start the engine so therefore the engine only cranks, and after 2-3 mins, the alternator will automatically recharge itself and then everything will be running as usual?

Appreciate any feedback.
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post #25 of 45 (permalink) Old 08-27-2004, 10:33 AM
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RE: Starting Failures *URGENT HELP NEEDED!!

Quote:
the_girl_i_love - 8/27/2004 7:21 AM

The above readings 12.5 - 12.6 volts show when the with the engine running somewhere between 2000 to 2500 rpm.
Do you get the same reading under load and with everything turned off? I am assuming that you measured the voltage at the battery, what is the voltage at the alternator? If you get the same voltage with the fast idle at the alternator, then the alternator needs to be replaced.

The only thing that seems to be out of sorts here is that some mechanics say your charging system is ok. Someone is not doing the measurements correctly.

Quote:
My alternator may be working fine but it is not charging sufficient electricity to the ECU (if there are not faults) to start the engine so therefore the engine only cranks, and after 2-3 mins, the alternator will automatically recharge itself and then everything will be running as usual?
Alternators do not store charge. An alternator produces a voltage and supplies current once the engine is running. If the car does not start, there is no output from the alternator. It is the battery that supplies the power for starting. The question is the battery getting sufficient charge from the alternator and is the battery in good condition if the alternator is in fact good. A bad battery can make some of the voltage measurements appear low, as can certain problems with the alternator when you measure the battery with the car on or off.

How old is your battery? When was the last time it was tested (load pull)? How often and for how long do you normally drive your car? Having to double start is also a symptom of a battery that has about had it or is being drained because of current being drawn. An abnormally high current draw when the car is off can deplete the battery charge and cause this kind of problem or give you a dead battery depending on the amount of current, how long the car sits, how long you drive the car when you do use it.
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post #26 of 45 (permalink) Old 08-27-2004, 01:40 PM
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RE: Starting Failures *URGENT HELP NEEDED!!

12.5 to 12.6 volts is not enough to maintain the power needed for the car and charge the battery, at 2000 to 2500 rpm the reading should be 14.5 minimum, your alternator is shot replace it, don't bother rebuilding it or changing the regulator because i think its deeper in to the alternator where the problem is "probably a worn armature" as you mention they did replace the regulator twice so taking that into account its obvious the fault is the complete alternator[:)]
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post #27 of 45 (permalink) Old 08-27-2004, 07:20 PM Thread Starter
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RE: Starting Failures *URGENT HELP NEEDED!!

Quote:
Alternators do not store charge. An alternator produces a voltage and supplies current once the engine is running. If the car does not start, there is no output from the alternator. It is the battery that supplies the power for starting
Reply: Guess what happened. I did not start my car for the last 24 hours at all. But this morning when i was about to go to work, the problem happened again (cranking sound, infrared lights flashing and can be start after 3 mins) Does the alternator has anything to do with this as i understand, the car was not used for 24hrs and therefore, there is suppose to be no energy from the battery was being used/ drained.


Quote:
How old is your battery? When was the last time it was tested (load pull)? How often and for how long do you normally drive your car?
My battery is very new, i had it replaced just 4 weeks ago by the MB dealer (they advised it part of the procedure to trace my problem). I drive my car on a daily basis, average 3 times a day;
(1) Going to work (15mins drive)
(2) Going for lunch (10mins drive)
(3) Back to the office (10mins drive)
(3) Going home (20mins drive)

Any ideas?
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post #28 of 45 (permalink) Old 08-27-2004, 09:30 PM Thread Starter
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RE: Starting Failures *URGENT HELP NEEDED!!

Guys,
the above picture in the above post was the result i got at 10am after Workshop diagnosed my car. (sorry, i do not know how to attach a picture in a new post)

any comments?
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post #29 of 45 (permalink) Old 08-28-2004, 06:34 AM
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RE: Starting Failures *URGENT HELP NEEDED!!

yep thats about right a faulty alternator would cause that "lack of charge to the battery" and that would make the warning lights come on and store soft codes in the ECU
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post #30 of 45 (permalink) Old 08-28-2004, 09:40 AM Thread Starter
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RE: Starting Failures *URGENT HELP NEEDED!!

Refering to the attached results,the conclusion to solve the problem is to replace an alternator. I'll to see what i can do and i'll update you guys.
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