I bought a 2002 E320 w/72k miles4 months ago and my check ingine light came on2 months later.Service B was exceeded by 4k miles.I start getting a bad idle after light came on and loss of acceleration.I got a code of P0301(misfire in cylinder 1) when tested.Ifirst replaced my spark plugs(all 12), second replaced my ignition coils(all 6), and I got a lil bit better acceleration buttheCEL stayed on.I replaced my fuel filter3 weeks ago and my acceleration was alot better but the problem wasnt fixed as the CEL stayed on and car stillidled bad at take off(better than it was but not normal).I replaced my mass air flow sensor(MAF) last Thursday(11-15-07) and my idle isnt as bad and my acceleration is better but my CEL is still on.Does it take a certain amount of drive cycles for your car to runthru before the CEL goes off or should it go off immediatly after the problem is fixed? Is it a computer problem? I cant see the whole word "off" that pertains to the air conditioning or heat b/c of the words being broken due to something w/the computer in my car.My car is running alot better than before after replacing the fuel filter and maf but my problem is obviously not fixed.Could there be something wrong w/the computer in my car thats not reading something right thats causing my CEL to stay on?Should I drive it a lil bit longer to see if it goes off?Should I disconnect the battery cables to see if goes off?My next option is taking it to the stealership b/c I have no clue what my problem is.Any help would be greatly appreciated.Thanx in advance.

 

First of all, keep all you old parts. They will come in handy later for troubleshooting, or use them for spares

Second, don't feel too badly about not identifying the problem on the first second or third guess. Most of the time, when I have a difficult problem that I haven't been able to figure out, the experts are rarely able to do any better. Of course there are typical problems that are identified on the first shot, but I rarely take those to the dealer. These cars are very complicated, very proprietary, and quite frankly the books offer only weak clues. So i understand your desire to do this yourself.

Have you confirmed the three basic needs for combustion in that cylinder, are you getting a spark? is the fuel injector spraying fuel, have you tested the compression in that cylinder? Blue

 

I think that my fuel injector might be leaking or spraying fuel b/c my mechanic told me that the spark plugs in cylinder 1 were coming out wet after replacing and driving for a min. He also told me I was getting a "ground" connection instead of a "pulse" like the other cylinders are getting. Anyone think I need a new fuel injector? Where can I find a new fuel injector for a 02'Benz E320 online or in the Dallas,TX area. The Mercedes stealerships sell them for $225(If I remember right). Any additional help tothis post or my originalwould be appreciated.Thanx.