I have a 1993 300E and the battery is new. I checked it with a DMM and I'm getting 11.87 volts while the car is running at idle a/c off. It dips to 11.22 with the a/c on. I'm thinking its alternator time but wanted to see if anyone had any other ideas before I spend the money. I'm used to american cars that put out around 14 volts while running.

 

1) Check belt tension
2) Check voltage regulator

3) If both the above have been checked or replaced, alternator is probably almost dead.

 

Is the regulator external on these cars? I have been a mechanic for a while but new to euro cars.

 

The regulator is attached on the back of the alternator. Two screws and it is in your hand. You can check the brushes to see if they are worn down, but I would honestly just replace it unless it looks brand new. May save you $180+ and it is one the "must-have" safety trunk items.

 

Thank you ps2cho I will try that first.

 

What was the final ailment and fix?

I am having low voltage reading (11.7ish volts) in an otherwise good running e420 my94

 

It turned out to be the alternator. The regulator is on the back of it and nobody stocked just the regulator anyway, so I changed the whole thing. The hardest part of the whole swap was the pulley has to be taken off the old alternator. I changed my belt at the same time and that wasn't much fun without taking the fan off.

 

Pulley comes off easy as pie with an impact driver.

 

I first ordered a new voltage regulator for my low voltage(11.7ish) issue, then decided I would go ahead with an upgrade from 110 to 143 amp alternator. I did research from this and other sites to find the right spec and fit. it was an easy swapout - possible from many other MB's. The rectifier, and thus the regulator, was rotated somewhat. The wires still were long enough to connect........ the results............

The entire car is on steriods.. the radio sounds fantastic for the first time since i have owned the car. my power hungry dell m6300 (3d video card) runs without automatically going into powersave mode, my nav system is more responsive to touch and the tracking refreshes are quicker, my headlights are brighter of course, my V1, XM, etc..., and the best improvement is a big surprise - the acceleration is noticeably improved .

now....for those that question the upgrade, or feel that it will cause burnout of any equipment, well, my voltage is back to the 12.8-13.8 range. This is normal and will not cause anything to burnout prematurely. The amps are also regulated, meaning the amps are called upon as equipment requires it and 143 amps is not just forced into the system unless needed by the aggregate equipment. This principal of electricity and regulators prohibits premature burnout also.

it works well beyond my expectations and EVERY w124 owner should upgrade. you can not get more improvement in our cars for only $150 dollars.

 

Did you do this on your e420 or your 300e? I upgraded to a 150a unit from a clk430 and to my understanding, the upgrade is only a direct swap for v8 cars.

 

Is this the case for '95's as well (I've got an E300D)? I've got a USALT-2031 alternator (90 amp) on there now. Online, it says that it's "internally regulated."

I'm trying to track down a reasonable/correct replacement regulator (Mercedes wants $130.).

 

in this case we are stuck with old nomenclature. Your regulator is internal, but it is separable from the altenator. the "internally regulated" term arises from days when the majority of regulators were mounted on the firewall. The few internals were "of note" Now it is just the opposite, the vast majority are internal. Now as far as what % are separable from the generator.... who knows, but our bosch's are as far as i understand.......

........ here ya go.......

http://cgi.ebay.com/ebaymotors/alter...Q5fAccessories

 

E420 was upgraded...... the active bass is really active.... I try to keep my original stuff, so i have lived with the mediocre system for 15yrs.... now I am going to see if I can pull some sizzling highs to go with the amazing lows..... did not know it could sound this way.... still having fun with my old MB.

any suggestions for the high not reproduction?

I am going to research the 300e alternator upgrade. it is a 1990

 

My car was already on at least its second alternator (this one was installed 10/07). It's a NSA alternator (aftermarket OE spec and new/not re-manufactured).

I called their technical support line and spoke with a guy who pulled an identical one off the shelf and looked it over. In my case, the voltage regulator is both bolted (same as the one you linked to) AND soldered. He wasn't sure if a Bosch part would be interchangeable with this alternator.

I need to minimize the amount of time the car is sitting on ramps (I live in an apartment at the moment), so I'm going to go ahead and replace the whole unit to minimize the likelihood of me having to crawl back under the car again (i.e. if the brushes or another component are bad). I was hoping to be able to take the cheap route, but it looks like that's out. I appreciate the information.

 

The bosch "mercedes spec" alternators frequently lasts 200,000 miles plus - some are never replaced. Of course a percentage will roll off the assembly line with inherent flaws to be revealed as lower mileage failures. my 300e has 275k on the original alternator, but on its 3rd regulator (100k per regulator??).

That said, I would buy even a low mileage used over a "non-bosch" new. BUT, the bosch can be had for $125-$175 rebuilt - that would be my first choice.
I disassembled and checked the 143 amp upgrade I recieved as a rebuilt. The slip rings (rotates against brushes) looked to be less than 50,000 miles as compared to my 120,000 mile E420 unit. The bearings were new. The rebuilt is in great condition. Do not be afraid to go that route. Even my old unit looks good for many more miles and could make a good rebuild candidate.

 

Yeah...the man I spoke with didn't sound shocked that it died with ~three years and less than 30,000 miles of use. The car is coming up on 290,000 miles, so there may be some other part that's worn and putting a strain on the system (who knows).

I looked around and the cheapest refurbished Bosch was WELL over $200. I bought a knock-off (will come in tomorrow) for $140 (it's built on a Bosch core). This one actually has a better/longer warranty than Bosch too.

I'll pull the old one and see about re-building/keeping it around as a spare. The Land Cruiser gets ~12 MPG and sucks for commuting, so I'm just itching to get the car back on the road ASAP.

 

out of curiousity, is there a problem with this item. I know the rebuilder is reputable as i have seen the name for years and used them many years ago - its bosch and the price is right.

http://cgi.ebay.com/ebaymotors/MERCE...Q5fAccessories


A rebuild would consist of checking for trueness of rotating components. verifying/testing rectifier for bad diodes or signs of overheating. checking rotor and stator for shorts or fray. The certain replacements would be the regulator (with brushes) and bearings. If the unit has not been physically damaged, a thorough cleaning and testing should be it. I am not a rebuilder, but this should be close to the process, and it seems to covered by this auction and bosch and less than $100 bucks. It was the first auction I came upon, but there were others from other rebuilders.... just curious

 

I'm not sure why it didn't occur to me to check ebay. I guess I was in a hurry. You're right...the price certainly is right. If it comes in tomorrow morning as they claimed, I'll be happy.

 

The alternator isn't the issue. I went ahead and replaced the alternator last night and I'm still having the issue. When I turn the key over, I'm hearing a slight 'clicking' sound under the hood. I'd assumed that was the starter, but maybe that's pointing to another issue?

 

WAIT....... we have hyjacked the thread........ I was looking at the initial explanation of 11.7 volts being the issue by paul81rx&.....

What were your symptons ?

 

Yup...If I have an issue that seems like it would be common, I try get into a related thread (i.e. this one) to leech off the knowledge base.


I fixed the issue this afternoon. The original cause of the problem problem...the alternator was in the process of failing and had been draining the original battery.

I installed a new Mercedes battery which seemed to fix things for about a month. Once the bad alternator had a chance to start drawing down the original battery, the electrical gremlins started up.

As the new battery seemed to be fine (tested with a volt meter), I went straight for the alternator. When I replaced that and tried to start the car...no luck. It was at that point (two days after testing the battery) that the battery only showed 11.7v. I took the battery to advanced and they charged it up. The car now runs fine. I just have to figure out why the RPM gauge is now inoperative (fuse maybe?).

If I'd realized that I could remove the alternator in under 30 minutes without even jacking the car up...I would have had it tested before spending my money on a new battery. Hindsight being 20/20, that would be my first advice to someone encountering this issue.

 

about two years ago my lamp out indicator lit. After several wire chases, I determined the it was the module. Decided that since all my lights were fine, I'd put a piece of electrical tape on it. intending to get the module soon. After a few months, the issue was forgotten, tape ignored.

After I upgraded my alternator due to my low voltage problem, the bulb out light has extinguished. Of course all the lights are still fine. remember, during the time my voltage was low (now determined to be about 2 years), I never recieved any electrical system failure/warning lights.

I added this so that any searches for a failed lamp indicator of module will give this result. It could actually be the voltage regulator/alternator.

didnt know the light out indicator and the voltage regulator were related....