White smoke is usually an indication of coolant being burned through the exhaust. Which could mean you have a blown head gasket.
If your computer isn't displaying any codes for the misfire, then you know the primary half of your ignition system is functioning correctly. So you need to check the secondary half.
If you've replaced coils/wires/plugs, and your misfire is isolated to only the No.3 cylinder, then either something is fouling that plug, or the fuel injector for that cylinder is clogged/faulty.
To check, run your vehicle until you experience the misfire. Then immediately shut the motor down and pull the plug for that cylinder.
Look at and smell the plug. If it smells like fuel, then you know your injector is at least spraying fuel, but not firing.
If there's a shiny black on the plug tip, then that's oil fouling the plug. Which means you either have worn valve guides, or worn piston rings.
If the plug is wet, but not from oil or fuel, then that's coolant, and you've blown a head gasket. (which would explain the white smoke)
Jan 7, 2010 at 2:00 AM
