The tale of the misfire
03-20-2010, 10:18 AM
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1997 E320
The tale of the misfire
A few months ago I posted a question about a misfire I had on my 1997 E320. With a new baby that we are blessed with I lived with the very annoying misfire but finally yesterday it was resolved!
A bit of a background. The car started misfiring at first randomly till about a month after the first indication constantly. I always took the car to the dealer, they had a discount for older cars and they are located right next to my old job so it was really convenient. They had been fair up to that point so I was fairly pleased with them. Their diagnose to the issue was that I needed a new wiring harness. The engine was misfiring on cylinder number 2. That would have set me back a couple of grand and I thought long and hard about it as my car has 260000 KM and its worth is probably a couple of grand.
I decided to hold off and do some more investigation. I posted on this board the issue and got a couple of responses which I investigated. Unfortunately the issue remained. I decided to explore a shop that is close to my house and its parking lot is always full of old mercs.
I took the car in and I told the mechanic the dealer diagnosis as well as my own. I also told him that 15k ago I had changed all the sparkplugs and the coil on cylinder number 2. Hi doubted that the harness was an issue, he said that he normally see that problem up to 95 but in my specific model he has rarely changed out the harness. He cleaned and swapped the spark plug out of that cylinder as well as the coil. The misfire continued. Recently he had a flood and his Mercedes diagnostic was damaged so he was waiting for a new one. His other diagnostic tool was just showing the misfire but could not specify the cylinder. He asked me to drive the car for a couple of weeks as he wanted to see the deposit on the spark plug. He theorized that I could actually have a valve issue related. I questioned this but I figured, I have nothing to loose. I went back yesterday. Now he plugged the Mercedes diagnostic tool and it showed misfire on cylinder number 1! He takes out all the plugs, sure enough the number 1 plug was black, but more interestingly cylinder number 2 plug looked brand spanking new! At that point he agreed with my assumption that it must be the coil as there is no way that a valve is having an issue and with fairly new plugs the coil must be bad. The coincidence here is that the coil was swapped to cylinder 6 which feeds also cylinder number 1. He gets another coil, puts it in, fires up the engine and the same crap... In the meantime he took the plug from cylinder 1, cleaned it and put it on cylinder number 4. He plugs the diagnostic tool... Yeap cylinder number 4 is now misfiring! Bloody damn plug!!! Sure enough it was the spark plug!!!
I'm thankful that I dogged a huge bullet, lesson learned from my experience is that despite the fact that you may have new plugs, always question them first!
Now I'm ready to cause some fuss at the dealer :p
A bit of a background. The car started misfiring at first randomly till about a month after the first indication constantly. I always took the car to the dealer, they had a discount for older cars and they are located right next to my old job so it was really convenient. They had been fair up to that point so I was fairly pleased with them. Their diagnose to the issue was that I needed a new wiring harness. The engine was misfiring on cylinder number 2. That would have set me back a couple of grand and I thought long and hard about it as my car has 260000 KM and its worth is probably a couple of grand.
I decided to hold off and do some more investigation. I posted on this board the issue and got a couple of responses which I investigated. Unfortunately the issue remained. I decided to explore a shop that is close to my house and its parking lot is always full of old mercs.
I took the car in and I told the mechanic the dealer diagnosis as well as my own. I also told him that 15k ago I had changed all the sparkplugs and the coil on cylinder number 2. Hi doubted that the harness was an issue, he said that he normally see that problem up to 95 but in my specific model he has rarely changed out the harness. He cleaned and swapped the spark plug out of that cylinder as well as the coil. The misfire continued. Recently he had a flood and his Mercedes diagnostic was damaged so he was waiting for a new one. His other diagnostic tool was just showing the misfire but could not specify the cylinder. He asked me to drive the car for a couple of weeks as he wanted to see the deposit on the spark plug. He theorized that I could actually have a valve issue related. I questioned this but I figured, I have nothing to loose. I went back yesterday. Now he plugged the Mercedes diagnostic tool and it showed misfire on cylinder number 1! He takes out all the plugs, sure enough the number 1 plug was black, but more interestingly cylinder number 2 plug looked brand spanking new! At that point he agreed with my assumption that it must be the coil as there is no way that a valve is having an issue and with fairly new plugs the coil must be bad. The coincidence here is that the coil was swapped to cylinder 6 which feeds also cylinder number 1. He gets another coil, puts it in, fires up the engine and the same crap... In the meantime he took the plug from cylinder 1, cleaned it and put it on cylinder number 4. He plugs the diagnostic tool... Yeap cylinder number 4 is now misfiring! Bloody damn plug!!! Sure enough it was the spark plug!!!
I'm thankful that I dogged a huge bullet, lesson learned from my experience is that despite the fact that you may have new plugs, always question them first!
Now I'm ready to cause some fuss at the dealer :p
