CLK 240 engine management warning light

[graham.l]

Recently had the engine management light (EML) come on when driving on the motorway and car started to misfire. Garage diagnostics indicated a misfire on 3 cylinders, I had the garage replace all 6 coils along with 12 new plugs and leads, car performed like a dream, until yesterday when another drive on the motorway and the EML came on again and the misfire all over again. Garage diagnostics this time, indicate all 6 cylinders misfiring now, which is impossible. The only common denominator between the two periods of misfire was that I filled up with petrol from two different supermarket garages just before my motorway drives, could it be cheap fuel?
My car is a 2004 (54 plate) with 88K on the clock

 

[BlackC55]

Recently had the engine management light (EML) come on when driving on the motorway and car started to misfire. Garage diagnostics indicated a misfire on 3 cylinders, I had the garage replace all 6 coils along with 12 new plugs and leads, car performed like a dream, until yesterday when another drive on the motorway and the EML came on again and the misfire all over again. Garage diagnostics this time, indicate all 6 cylinders misfiring now, which is impossible. The only common denominator between the two periods of misfire was that I filled up with petrol from two different supermarket garages just before my motorway drives, could it be cheap fuel?
My car is a 2004 (54 plate) with 88K on the clock

You need to take your car somewhere else. That engine will never need that amount of coils in one hit!

I suspect a faulty air mass sensor.

 

[graham.l]

Thanks for your reply, I asked the garage to replace the other 3 coils and plugs and leads to ensure that all was ok.
Unfortunately this hasn't solved the problem, I will now ask them to check the air mass sensor.
Thanks again

 

[jacksona]

You need to find a different garage if you're telling them what to do to try to fix it!

 

[graham.l]

good point, anyone know a reliable indy garage in the Liverpool area?
don't want to pay main dealer prices.