octane and eliminate knock. I did the resistor mod and started blending e85 with premium in 2010. Recently when I replaced the transmission I installed a new knock sensor and harness. If egr valve is not in the way, it can be done with engine in the car. A little tricky but I practiced how far back to reach with two fingers. Then with the sensor and bolt between two fingers, reached in and the bolt just dropped into the hole.