My SLK has a slight misfire at idle. Mercedes have had it for a week and cannot find what is causing the fault yet they intend to charge me for labour - having achieved nothing. Is this standard practice in the industry for a manufacturer which wants to keep its customers???

 

And heres a new twist. In order to continue to investigate the misfire problem they need to take parts from a donor car to fit to mine to experiment with. They want to charge me the labour for removal and replacement of said parts from donor car. Mercedes will not provide parts to 'play with'. What sort of Mickey Mouse outfit are Mercedes turning into???? This is supposed to be one of the top car producers in the world. They are becoming a laughing stock.

 

Hey Finman;

A small miss at idle is usually the following:

Uneven fuel flow caused by contaminated injectors, a plugged fuel filter, a worn fuel pump. Try running a bottle of LUCAS fuel treatment in a tank of gas (about $3) and see if you get a change in behavior, then try a different brand of gas. you may be getting too much additives in the mix... like alcohol.

Old oil. Really!

A loose cam chain (older motor)

Poor air flow. air filter worn?

A loose spark plug cable connection or a worn or damaged ignition parts. Probably not these if no codes lead the tech to this. But, you should carefuly inspect the cables yourself. Improper spark plug gap and carbon build up on one or more pistons also cause a miss.



When I worked at a dealership back in the 80's, we ran into problems like this all the time. We charged time and materials for all the above experimenting. It was necessary due to employment costs and the use of electrical parts that copuld not be resold after use. You are lucky they have donor parts, this is rare. I would do a little work on your own before returning to the dealership. My guess is you will find the cause.[sm=gears.gif]

 

They should not charge you for something they cant find and if they need another car to swap parts on then I wouldnt say they are good techs. Take your car somewhere else!!

 

Hey Drew

Thanks for the comment. Nice to know there is someone out there with some knowledge. Sadly, my mechanical skill is limited to putting the fuel in - to quote Donald Sutherland 'I just drives em, I dunno whats makes em work'.

The car has had new plugs (12), new ht leads, new oil, full service at UK£800 (US $1300). They have resoldered all the electrical joints. They have just swopped out the fuel rail (whatever that is/does) with no result. Thankfully, when I told them I would not pay labour for getting donor parts they eventually agreed to proceed anyway. I am still faced with another labour bill of £300 to add to the previous £400 and still no result. AAAAARRRRRRGGGGGHHHHH! They are going to contact Mercedes technical HQ for their suggestions as to what to try next........probably at my expense too....

 

There may be carbon build up on the pistons. I still think cleaning the injectors with a fuel treatment (approved by your mechanic) is worth trying. A clean motor is a smooth motor.[sm=drlove.gif]

 

I have the same problem... small missfire at idle... (2001 slk230, 35000km)... I will try fuel injectors treatment....

 

MINE does the same thing? Really, it is not a misfire for me, the motor shakes noticibly different when the air conditioner compressor is on. Could you be experiencing the same thing?

 

Of interest, Mercedes have had my car for a further 3 weeks - thought they found the cure with a new FCU but the problem remains. Pretty sure it is not associated with the AC. They are going to get the tech experts from HQ in tomorrow for their opinion -(why has it taken 4 weeks for them to get to that idea!!!!!??????)

 

Another point. When I was checking out the car after their last effort, I slowly revved the engine up (when warm) to see if there was any other misfire of notice. When I got to 4300 RPM get big misfire. Mercedes says it is supposed to do that when the car is at rest to stop over revving. Anyone else with a 320 that can confirm that idea. It is not mentioned in my manual!