F5fstop, info you posted I believe is correct solution. After I cleaned 5&7 Plugs did comp. test switched gas stations and added jug of injector cleaner problem is gone. Mileage decreased about .5 mpg, 12 to 11.5. I found that strange until my son The Heavy Truck mechanic explained it saying map and 02 sensor recognize rich mixture because of missfire so auto. lean out mixture. So in summary I believe fuel rail cofiguration causes 5 & 7 to fail first with any contamination in fuel. Regards The Rebel
