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Marty
Marty, Mercedes Technician
Category: Mercedes
Satisfied Customers: 54026
Experience:  Bosch Certified Master Tech. Over 35 years experience.
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Mercedes-Benz ml 63 amg: hi,my ml 63 amg when i accelerate

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hi,my ml 63 amg when i accelerate i hear a rattle sound for couple seconds. my dealer has checked on computer no faults came up.he thinks not engine! to me sounds like the old pinking noise !!any ideas what it could be

eurotec :

Hi, as you can imagine, diagnosing a noise over the internet can be difficult. Having said that, one of the most common things that I find on the ML relating to a rattle on acceleration is a loose catalyst element inside the catalytic converter. When the catalyst breaks loose it will give you a rattle on acceleration. I'd have the converters checked for a loose catalyst element.

Customer:

thanks.rattle more noticeable when going up hill

eurotec :

I'd have to suspect the converter for something like this. It's a rather common problem on the ML.

eurotec :

I do not think that it's an engine ping. There are sensors on the motor that correct pinging.

Customer:

is this an expensive repair

eurotec :

Unfortunately it is. The converters are in the $800 - $1200 range but lately Mercedes has come out with remanufactured converters that are very reasonable. You'd have to have the dealer check availability if you need a converter.

Customer:

does my car have two of these having twin exhausts

eurotec :

Yes it does, one on each side.

Customer:

you deffinately dont think engine

eurotec :

Without hearing it it's hard to say but I doubt that it's an engine ping. I assume you use premium fuel. If you are using a lesser grade I'd switch to premium.

Customer:

i use normal unleaded 95, dealer said not 98 !

eurotec :

95 is fine, you're octane rating must be higher over there. Premium here is 93.

Customer:

ok so you think cat need replacing

eurotec :

I think that you should have them checked for a loose catalyst element.

Customer:

do they have to take exhausts off to check this

eurotec :

No, they use a rubber mallet to bang on the converter housing to see if it rattles.

Customer:

if no rattles their ok then ye. back to engine

eurotec :

Correct, but it would be most unusual to have a rattle from the engine.

Customer:

i hope your right, the engine still does have that "growl" when i accelerate, when im in low gear that rattle comes again

eurotec :

I do think that a loose catalyst element is the most likely cause. Without actually hearing it I cannot be sure but it's a pretty common complaint.

Customer:

ok thanks for your expert advice, ill have cats checked tomorow, hopefully your right and i finnaly get to bottom of this problem. maybe thats why dealer trying to fob me off with other maybe's !! last week he thought something might be loose so had eveything tightened up but still same noise!!

eurotec :

You're quite welcome. If you have any further questions you can always reply back to me even after you rate my service. Follow up questions are always available to you.

Customer:

last thing you deffinately dont think its misfiring

eurotec :

Definitely not, if it was misfiring the check engine light would come on and most likely the computer would shut down some cylinders and the car would run rough after the misfire occurred.

Customer:

ok great. i hope your right. just to clarify then, it only occurs when in low gears going up hill for example or i put my foot down to accelarate. still sounds like you said, loose elements in cat!

eurotec :

Yes that is correct, when the catalyst is loose it tends to rattle on acceleration.

Customer:

ok now you get paid !!!!many thanx

eurotec :

You're quite welcome :-)

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