Join Date: Apr 2002
Location: Dandridge (Near Knoxville), TN, USA
Originally Posted by ojalpert
I am from Scandinavia and normally I use Shell V-power 99+ octane fuel, becasue it's working absolutely the best. I removed sparkplugs after 100 miles driving and one of them was quite "black" and other ones were normal lightgray. What are you thinking guys should it be possible that one injector not working well. Too rich mixture to one cylinder and after that Lambda loopback control tune the wrong mixture to the motor.
If you have one black plug it could be a leaking injector causing that cylinder to run rich. Normally if the ECU (Motronic) was sending injection pulses that were too long at least TWO cylinders would be running rich. I am pretty sure that two injectors each are controlled by two firing pulses.
A black plug can also be caused by oil bypassing a ring or intake valve guide, but that coating will be rather shiny and "wet" looking, where a rich mixture will cause a dull "powdery" black coating.
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