HELP HELP HELP w219 battery alternator fault

[Ted]

When you say nothing, do you mean zero ohms or infinity? Anything that is not zero definitely needs investigating further.
I've known fully insulated alternators, but that is on trucks not cars.
One other thing, voltage dropping when you rev is a classic sign of a slipping fan belt. I'm sure it's not that.
Best advice I can give you at this stage is to fully charge the battery and take it to a reputable auto electrician.

 

[brucemillar]

If worried about earthing? Could you not put a jump lead from the alternator case to earth, just to test?

 

[revajones]

Yea I get zero ohms from the multimeter. On everythromycin other earth I get a low constant reading but nothing from this alternator ,

I don't suppose you could recommend anyone in the south wales area. I only ask as the car was in a mercedes specialist the past week any they diagnosed this at my expense as the alternator yet it was not that . They ahve said the ecu is asking the alternator to raise voltage it just isn't raising .

The belt feels and look in good condition and tight to me it appears pretty new altho I will check it tomorrow

Thanks again't for all your help

 

[revajones]

And Bruce I tried this yesterday but the jump. Lead was sparking when I touched the alternator to didn't want to fry anything . If you guy think it's OK I'll try it again and see if the voltage increases

 

[Ted]

Alternator body to earth sparking doesn't sound right at all.

 

[revajones]

That was my thought on it ,

I'd it possible the live from the alternator is touch the engine in some way ?

I know ghetto jump lead I used heated up tremendously. That's usually a sign your earthing a live am I correct

I will check if the alternator case has an voltage in it tomorrow

 

[brucemillar]

I agree with Ted. That is not correct. It sounds like your alternator case is live or the entire engine is live and so putting a current through the alternator. That may well be the problem. I think you need to get it to an auto electrician.

Sent from my iPhone using MBClub UK

 

[topdown]

Alternator, ECU and battery sensor are connected by data cables so 'sparking is not good as it could fry these units.

 

[Ted]

Something isn't right here.
Put a voltmeter between the alternator body and a good earth on the body. There should be no voltage. Anything else (other than a few millivolts) should be investigated. There is no way that there should be any voltage there.
If there is zero voltage then Bruce's (correct) suggestion that you should try some jump leads between the engine (or alternator body) and earth cannot result in a spark (Ye canna change the laws of physics captain)

Bottom line is that if there IS a voltage between the alternator body and earth, then something is very wrong. I would expect the engine earth strap to be ok as the car starts ok, and I would expect this to provide the earth for the alternator too (it may be possible that the alternator is insulated from the engine via rubber mounts - in which case it WILL need an earth.
I can't see any way that putting a jump lead between alternator body and chassis earth will cause a problem. If it sparks without the engine running you have a problem. If it doesn't spark with the engine running but sparks with the engine running then my guess is that the alternator needs an earth cable and it is either missing or broken.

Remember you are only getting advice from a bloke on the internet who can't see what is happening, and is taking your word as gospel (I'm not doubting you by the way)

Given the above, I would still take it to a reputable auto electrician.

I would still be interested in what the diagnosis is.

 

[revajones]

Well after another expensive day it appears I may have made the break through my self tonight


I measured the voltage at the alternator with the muktimeter earthey on the car it was showing 12.5v so out of interest I earthed it on the alternator body

To my amazement it was running 14.2v in fact if I earth the multimeter anywhere on the engine it reads 14.2v or around that figure

So I took a jump lead again earthed the engine to a earth post on the car an have managed to get the voltage at the battery up to 13.7v as soon as I remove the jump lead it drops back to 12.4v

So I'm guessing myself the engine earth point are either corroded or one or twould are missing


Does anyone agree with me here pr.may there be another solution?

Would anyone happen to know the location of theengine earth's etc

Thanks again for all your help guys

 

[Ted]

Certainly sounds like the engine to chassis earth is bad. The mystery there is how the engine turns over.
No idea where the original engine to chassis cable is, but until you find it you can run one between a good clean engine point (starter mounting bolt?) and a good earth on the body or even the battery negative itself.
May be worth tracing the battery negative cable to where it bolts to the chassis and pitting your cable there. This point may even be where you're problem is.
If you do run a separate cable it needs to be as thick as the existing large cable on the battery negative, have enough flex for the engine to move, and not rub up against any live connections.
Good luck - I think you're nearly there.

 

[revajones]

I believe this is the issue I agree

Well sometimes it will not turn over it just thought it was because the battery is dead ito sounds like it's a bad earth not allowing it to earth sometimes


Again thanks for your help mate

I will update when I have added the earth's on tomorrow

 

[Ted]

Well sometimes it will not turn over it just thought it was because the battery is dead

Now, if you'd said that earlier...

 

[revajones]

I was thinking that my self actually haha I do apologise

More frustrating I payed a garage £135 to check all the earth point they clearly didn't bother

 

[Ted]

No prob! Let's see what tomorrow brings

 

[revajones]

I also ment to ask could you recommend anywhere to download the workshop manual for the cls63

Kris

 

[Ted]

Sorry, can't help with that one

 

[theogeor]

Well after another expensive day it appears I may have made the break through my self tonight

I measured the voltage at the alternator with the muktimeter earthey on the car it was showing 12.5v so out of interest I earthed it on the alternator body

To my amazement it was running 14.2v in fact if I earth the multimeter anywhere on the engine it reads 14.2v or around that figure

So I took a jump lead again earthed the engine to a earth post on the car an have managed to get the voltage at the battery up to 13.7v as soon as I remove the jump lead it drops back to 12.4v

So I'm guessing myself the engine earth point are either corroded or one or twould are missing

Does anyone agree with me here pr.may there be another solution?

Would anyone happen to know the location of theengine earth's etc

Thanks again for all your help guys

Yep. Looks like your earth is the problem. It can be either a broken/cooked cable or corrosion on the connection points. Have you tried to check those ?

TG

 

[revajones]

hi guys

so today i had the chance to pick up a brand new braided earth strap form halfords

i found an spare threaded hole on the engine attached it to that and to one of the original earth points .

and to my amazment its all back to normal

the car is running 14.2 volts as if nothing ever went wrong.


its hard to believe that a mercedes specialist could not diagnose this fault after hunderds and hundereds of pounds later , i had to fix it my self


i cannot thank you guys enought for your help, i have been on many forums in the past few years and somtimes the members seem a bit usless, bu this is not the case with this one.

thanks once again

 

[brucemillar]

I think I would be asking your Mercedes Specialist for your money back. An earth check is a very basic check that I would expect any novice electrician/mechanic to carry out as one the very first steps in diagnosis. Given your description on here and the fact that fellow forum members were able to point you in the correct direction without having the car in front of them, tells you how basic and fundamental that check is. It takes less than two minutes to do and requires only the most basic of tools.

Any earthing fault on a car will lead to all sorts of "strange" behaviour with the electrics.