Hi,

My '99 SL320 with 40,000 miles has developed an annoying vibration when stationery in Park or Drive. I had the mounts changes and the car drives much better, but the vibration is still there. Feels like the engine is running a bit rough, but that's been checked too.

Help me please! It's driving me nuts.

Thanks

 

Hear it or feel it?

If you feel it ensure you have no DTC codes pending. You just may have an intermittent misfire.

If you hear it look for exhaust system foul, loose heatshields underthe car etc.

Stuart.

 

Hi,

Definitely feel it. Car shudders slightly when in Park and then I get a reasonably strong vibration (a buzzing feel)into the cabin / steering wheel when in Drive and with the brakes on. I had the engine checked and plugged into the diagnostics - nothing came up. How do I tell if it's a misfire - the engine certainly performs fine when moving?

The car has a pair of (rubbish) after-market Cats, but they're only noisy and not causing a vibration.

Thanks a lot,
Andrew

 

for a start it requieres a STAR DIGNOSTIC BYMB the cause of this judder is 99% ur coil packs, one your coil pack is on its way thats y its judder or shakin,STAR DIGNOSIS PICKS ANY FAULT UP THIS FAULT WILL BE PICKED UP ON ENGINE SMOOTH RUNNIG TEST,good luck mate...............let me no hw u get on.

 

Great - thanks for the reply Naz.

Andrew

 

If it is the coil pack surely this will show up as a misfire DTC on the cylinder(s) in question?

STAR is certainly an excellent BUT EXPENSIVE diagnostic tool.

Feel or Hear this vibration.

Stuart

 

Hi Andrew,

Sorry missed your reply.

Ok. Feel it. Any more info on when the problem started during your ownership or could we be talking a very sensitive customer picking up a characteristic of the vehicle which leaves room for improvement.

Wish we were still on the OE mounts. Were the new ones genuine MB etc? Unless you have rubber separation mounts are pretty robust and only 40k miles. Anyway thats water underthe bridge.

Can you feel the vibration on the engine. Place your hand on the plastic engine /air cleaner moulding?

Was your diagnostic check on STAR using NAZ's smooth running test or have you just accessed OBD DTC's on a scanner and found non. Presumably the smooth running test explores the misfire situation in more detail than the threshold set for normal DTC set.

Noise/vibration is so difficult to diagnose without the car in front of you.

However you staed you have rubbish (non OE) cats. Why do you refer to them as rubbish? Is the pipework EXACTLY the same as the displaced ones...I guess not since MB use in my experience often use a unique in/out pipe configuration dictated by a triangular shaped cat. Not sure what the SL uses. Are you sure the pipework isn't touching anywhere and possibly more importantly not stressing the mountings (will be less effective at attenuating vibration) as a result of the changed pipe run.

Cats cause back pressure on the engine and any change in this parameter can impact engine running but I guess this is unlikely UNLESS the problem can be associated to the fitment of the cats.

Stuart

 

Hello Stuart,

Yes, the vibration is new. It is like a buzzing vibration through the steering wheel, into the cabin and equally when feeling the engine I can feel a buzzing vibration which is in addition to normal engine movement. When in Park, the vibration remains and occasionally an additional rocking motion can be felt. The vibration becomes immediately obvious as soon as I pull up at lights and am stationary in drive. In short, the car feels really odd compared to normal.

I'm not sure about the Star analysis - I got a local independent who has the diagnostics to check for any fault codes. I live in London by the way.

The Cats are after market, which I didn't realise until I took the car in to check them as they rattle quite badly.

Andrew

 

you may have a vaccume leak around the intake manifold or hose

 

Hi Andrew,

I'm in Stafford.

You MB dealer has STAR and it is much more versatile than a straight code reader. Unfortunately MB dealerships have a habit of charging to tell you what is wrong unless you have some Goodwill banked...i.e. You have or you are goingh to buy a new car from them. Unlikely in my case!!

Rattling cats (especially when cold) highlight the fact that the monolith (ceramic catalyst block) is no longer correctly supported within the enclosure. The packing material has been blown away. This is not an aftermarket cat problem. Its a cat problem full stop and the MB ones are as bad as anybody else BUT more expensive. I just removed the monolith from mine to stop the rattling problem and nobody knows and it cost nothing. The secondcats are not required to meet UK emmission 3 year MOT standards so long as the pre cats are in good shape.

I still think your best cours eof action is to cough up for a STAR smooth running check ,,,what everthat is... and to ask that the dealership also look carefully for any foul between pipes, shields etc and the engine, body, steering rack.

You didn't provide any history about the circumstances when the problem suddenly appeared.

Sorry I can't be morehelpful.

Stuart.