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Discussion Starter #1
Hello,
I should start by saying I’m in love with Ruby! The ride, the power, the grace of this car is amazing.

I’ve spent some serious money at the MB dealer, rear struts, actuators, brakes, rotors, tires, starter, battery, oil pressure sending unit, central locking pump, and last but not least a complete service.

So here is the problem. When she’s cold the engine turns over fast and starts immediately. On short trips she starts right up, no change.
On a longer trip, the car running perfectly, oil pressure and engine temp normal, the battery seems dead when engaging the starter. The engine will barely turn over, service and warning lights go dim, try again and you even hear the tick of what sounds like a completely dead battery.
The first time this happened the dealer said it was the starter and I had it replaced. At the same time we replaced the battery with an almost new one.
I had no problems for a month or so (keep in mind my trips were short around town). Yesterday I drove the car 100 miles, AC on everything working perfect. Turned her off, turned the key on and the engine barely turned over, tried again, completely dead.
I went to my appointment and returned an hour later. The engine turned over very slow but started.
Drove home, again, 100 miles no problems, half the trip at night.

The next morning the car turned over like a highly charged battery. After a 30 minute trip with two very slow starts in between the battery went completely dead again. AAA used a battery pack to jump the car.

I had the MB dealer bring a new battery out. First he tested the battery and said it was good, and then a re-test showed bad. He went ahead and put the new battery in and the engine turned over fast and started. He let the car idle for about 20 minutes, turned it off, same thing, engine wouldn’t turn over.

What should I be looking at?
 

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1995 S420 19" giovanna's, tint, in-dash tv.1986 mustang LX supercharged 4 eyed pride~
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437 Posts
sadly I am of no help here, just wanted to say I love the color, and the ride looks great. sad to hear how much you have dropped into it and still no resolution. I am sure someone here will have a few more things for you to check out.
 

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1987 560SL - 1994 S420 - 2005 S55 AMG
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341 Posts
Have you had the charging system checked? A good battery will recharge if left alone for a hour or so. However short trips, with short intervals between starts, will drain the battery if the charging system is not working. Most Autozon will check the system for free.
 

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Current 1992 - 500SEL, W124 - 1989 230E (sold)
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Benz4mm first of all go and buy yourself a simple multimeter (for like $15 or even less) to test the voltage on the battery yourself (rather then buying new batteries or calling dealer over to "check" it) then check the voltage of the battery and it should be somewhere around 12V+ (possibly around 12.5V or so if not something is draining your battery or its not being charged enough) then check the voltage when car is running it should be around 14V (if its any less then your alternator isnt charging properly - could be several issues like voltage regulator etc.)

Let us know your findings, depending on that we can provide you more help from there....

This will do: (btw there is always manual on how to use it but if you get stuck i can help its very easy just one knob to turn the right setting and two leads for +/-)

PORTABLE ELENCO M-1000B DIGITAL MULTIMETER 100% WORKING - eBay (item 280229003681 end time May-27-08 18:46:49 PDT)
 

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It sounds like a bad Diode Trio to me.
its not converting the AC to DC properly, you might have a couple of dead diodes in the trio. What happens is that you feed a slight fluctuation into the system damaging the battery due to the AC cycling and causing permanent damage to the battery, at which it "Stabilizes" the Slight AC fluctuation...
I would suggest taking it to a Interstate Dealer and having a complete test done.
Be prepared for an alternator replacement. :crybaby2:
 

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Current 1992 - 500SEL, W124 - 1989 230E (sold)
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Hold your horses i think you are getting bit too complicated for start he should check basics just to make sure his car is even charging the battery as it should, and then go from there...
W140 are common for having failing voltage regulators on the alternator and its a cheap $35 part so no need to replace whole alternator just yet....
 

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Discussion Starter #7
Although i'm not sure exactly how to use it, i have a multimeter.
Testing with engine off the meter reads close to 12, i'd say 12+ (no exact science with this cheep meter) with engine running there is no difference...same reading.
Are we on to something?
Thanks for the help,
Mike
 

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Current 1992 - 500SEL, W124 - 1989 230E (sold)
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Should be like mine, if i do the same here with my 500SEL, when car is running iam gettin close to 14V with car off iam getting bit over 12V (and i have crappy battery anyway) so yes were are onto something...your alternator is not charging to the full potential, either worn or MOST likely voltage regulator! (do a search on this site and there are several discussions about it)

part is here for $27

Your Parts Search Returned 0 Part(s)


and i belive your alternator can stay in a car to replace the regulator...its just bit of pain getting to it
 

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1997 S600 (sold)
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4,660 Posts
Although i'm not sure exactly how to use it, i have a multimeter.
Testing with engine off the meter reads close to 12, i'd say 12+ (no exact science with this cheep meter) with engine running there is no difference...same reading.
Are we on to something?
Thanks for the help,
Mike
If your cheap meter is working properly, then you have a charging problem as mentioned. You should see over 14 volts when the car is running. I would expect that you should see the charging system dash warning lamp lighting up telling you that it isn't charging, but you didn't mention a warning lamp. Is the bulb burned out or removed? To check the lamp, turn the ignition to on, but don't start the car. Look at the instrument panel. All the warning lamps should be lit up. This is by design so that the lamps can be checked in this manner. If the charging system warning lamp is not lit up, the bulb is burned out or missing.

If it is just the voltage regulator, the part is cheap and easily available. If there are diode issues as well, I'm not sure how to get your hands on a rectifier. Depending on your confidence as a DIY mechanic, it might be best just to get a fully rebuilt alternator.

Brett
 

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1998 140.070 CL500, 1966 406.121 U65
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