I have a 2004 - S55 amg and in the past 3 or 4 weeks all of a sudden it is running like crap.

I took it to the dealership and they acknowledged that it was not running well, said that there were no codes present and suggested the following:
a) flush the tranmission oil
b) replace the engine and transmission mounts (they said that they notice extra vibrations)
c) replacign the spark plugs.

I have not had them do any of the above. I just paid for them to look at it first. But none of them except the spark plugs makes sense.

The issues is that for awhile, every 3 or 4 months, there will be a period of time that the engine seemed to have misfired. It was not like I would hear a misfire, but the when I would press on the gas the acceleration would be not be smooth and it will be like kicking in and out. the dealer at the time said that I should just add techron to the gas to clean the fuel or fuel line

but now I hear a hissing noise from the engine.

When i drive, the acceleration seems to have a hesitation and there seems like something is actually slowing the engine down. like in the old days when you have something stuck in the wheel of the bicycle.

When in idle there is some knocking noise coming from the engine ... not too much but a little ... actually someone the other day asked if my car was diesel (it is gas :-)

Can someone here help ?

I hate to spend a lot of money at the dealer for them just tell me it is somethign else. It has happened with my S500 and it was just a big waste.

The engine oil seems to be a bit darker than normal although i just changed it 4000 miles ago with Mobile 1. I am hoping that the shop actually changed my oil and filter since they charged me :-)

Thanks guys ---

I am pretty new to this forum but just found it as i was searching for answers.

 

Are you out of warranty? You must be, otherwise they'd be happy to do any test at all.

What about replacing the fuel filter and running a bottle of RXP in the next fill up?

It almost sounds like the engine could be starving.

Try posting the question on the E55 board, there are more hard core car guys over there.

 

Sounds to me that the super charger may be shutting down. Search the threads for answers on this common S55 problem.
Good Luck

 

DFW01E55 - thanks for your suggestion - i will post to the E55 as well. I just finally had a chance to replace the oil and filter today. I want to change my fuel filter too, as well as the air filter. I am "out of warranty" hence the reason for not running all kinds of tests :-)

the engine really is running rough in the past few days as things seem to have gotten worse.

thanks-

Hotrod-Realtor: thanks for the clue - i will check this out and will post my results online. Tanks again guys !!!!

 

I would do the original suggestions and also take a look at the intercooler pump. That is a very common problem with decreased power in 55/65/600 series cars.