Sudden death

wayner845

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ml55
Guys could really use some help my 2002 ml55 just died .It was like a total electrical failure for about 3 secs then all comes back on ,it will restart and tick over but as soon as you rev it once again it dies and comes back and you can start the engine again but it does exactly the same .It happened after some spirited driving using the gear shifter to change up and down.
Everything sounds fine nothing mechanical and no warning lights on restart/tickover. Ive checked the bty terminals and the bty with a multimeter and the alternator seems ok 14.5v on tickover at the battery .
Ive just realised the bty light is staying on which is strange as the bty is ok according to my multimeter as was the alternator .
Anyone any ideas.
Cheers
 
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wayner845

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Just been out to do a few more checks the bty is 12.5 volts engine not running,on tickover its reading 14.4v and if you rev it it goes all the way up to 17.5v all tested at the bty terminals.
Incidentally the car is now revving without cutting out now its cooled down but obviously something is not right.
 

grober

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Engine earth strap poor connection/corroded or CPS[ crank position sensor] on the way out?
 
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wayner845

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Thanks grober
The bty has died overnight for no apparent reason and ive been charging it now for about 3 hours but it doesnt want to turn over just a click.i will go out and check the earth strap soon .

Do i need to worry about the alternator producing over 17 volts at the bty when revved.Could it have fried the bty.
 
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wayner845

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Where is the engine earth strap exactly
 
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wayner845

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Cheers for the help ,
the earth strap is fine,ive just bought a new bty charger and it confirmed my old one is knackered as it charging fine now and starts but iam inclined to not run it till i change the alternator as it it reading 15.5v at tickover and just rises with revs.I think a new or recon alternator and a new crank sensor for good measure as it will just give me some peace of mind.
Has anyone any idea why the bty went flat over night,its now reading over 12v after a 10 min charge i will see how it goes.
 
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stevesey

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Sounds like regulator gone in the alternator if volts are rising to 17.5 and over when you rev the engine.

When the volts get that high lots of electric items start sutting down to protect themselves.

Had same on my Vectra years ago - instruments would cut out above 1500rpm. Other people who had same reported melted wiring on ICE amp installs etc - so drive it as little as possible and if you have to keep the revs down and the electrical load up (to help keep the volts down). I gingerly drove a couple of miles with lights and heated read window on to pick up the replacment alternator.

Interestly you mention it went after some spirited driving - mine went immediately after flooring it in second up a short but very steep hill with 5 up.
 

Ted

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Stevesey is correct, your voltage regulator is shot.
I don't know where it is on your car, but it is almost certainly integral to the alternator and can be replaced seperately.

The reason your battery is playing up is because it has lost some, if not all of the electrolyte - have you noticed a strange sulphurous smell of late?

My recommendation is to get the vehicle to a reputable auto-electrician at the first available opportunity to get the charging checked out/rectified (no pun intended).
You may also find that the battery requires replacement, as it will have overheated and could be damaged.
I would also not drive the car (except to the repairers) as you are subjecting all of your electrics/electronics to an excessive voltage. Even the bulbs will have their lives shortened at the voltage you quote.

Good luck - it shouldn't prove too expensive.
 
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wayner845

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Cheers stevesey ,sounds like i am heading in the right direction hopefully, now to find a alternator at a reasonable price any ideas.
 
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BlackC55

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Just replace the regulator they are available from mb parts dept. No need for an alternator. Very easy to replace too as it's on the back of the alternator. DONT run the car anymore. You could cause untold damage!
 
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wayner845

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Dont worry it wont be started again untill the regulator is sorted out ,i did plug it into my laptop using easy obd2 and no fault codes were found.the bty light stays on when running so the bty is probably nackered as already suggested.how much is a regulator roughly.
 

stevesey

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BlackC55

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Yes. It makes it much easier to do. Just unbolt it and turn it round in situ.
 
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wayner845

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Well I've removed the regulator from the alternator, I took the wheel and inner arch off which made it relatively easy to do.I've orders a new reg frm mercedes £37 not too bad I suppose ,and a new battery is on the way as this one is fried I hope nothing else is.I will let you know how it goes thanks for the advice so far.
Wayne
 
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wayner845

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Ok quick update got a new regulator from mercedes today and a new battery just fitted them both and it appears to be running fine .Took it out for 10 min all is well ,
Cheers to all for the input.
 

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