hi everyone, bit of a newby to the forum but must say its a great source of information for the MB owner out there...

i am having the following problem with my 99 model c280 v6 version... its has 190 000km under the belt and until a few days ago was faultless till i started it to head to work and there was a terrible misfire from the engine, initially suspecting the plugs i headed of to a local mechanic for an opinion, he plugged in his STAR dignostics and noted that cylinders 3 and 4 were far out of range on a "smooth run test" while the other cylinders ran bet 0.00-0.05 in range the bad cylinders fluctuated between 3.00 and 5.00... he then recommended replacing the coil packs and problem would be solved, with the misfire still evident and quite vigorious i then sourced 2 coil packs from a running c280 (verified the part numbers are identical) and swopped them out later that afternoon, started the car up and it purred as smoothly as before. took it out for a test drive and she ran smoothly for the first 2km before the misfire and power loss returned. i limped home and inspected everything to ensure nothing unclipped itself and found all to be fine, i unplugged the same 2 coils and replugged them and the car returned to normal again. i closed everything up and went to bed,

the next morning it fired up smoothly and under gentle use it ran the 6km to the office before returning to its old misfire habits, i loeft the car for 2 days at the office without use and when i statred it up again nothing had changed...

so? what suggestions might other posters have and what will solve this? obviously something else is the gremlin as the coil packs were swopped out, as well do the new coil packs need any sort of adaption and lastly how would i reset the ecu- this would come in handy when diagnosing/replacing parts instead of paying for another diagnoses each time.

i will be spending the weekend ahead replacing a new set of plugs in the process of elimination...

i really love this car and enjoy every moment of it...thanks in advance for all the help...

 

Try replacing the wires. I know there are two but jest one bad one will cause a miss. And also one misfire will cause another. So you only need to replace the wire for the cilender that is misfiring first and most often.