Ryan, I can't answer your question as to rich/lean but can explain to some extent what the 40% to 46% means. The ECU reads the O2 sensor and determines if the mixture is rich or lean and changes the duty cycle to adjust the mixture. In theory, 50% +/- 10% is ideal. If you adjust the mixture screw to a rich or lean direction, the ECU will change the duty cycle to get back to where it was, mixture wise. In other words, if every thing is working as designed 40% to 46% is neither rich or lean, it is correct mixture. Did that make any sense? In other words, you could turn the mixture screw a little one way and see what the duty cycle does. If it goes the wrong way, turn the mixture screw the other way. I do know you turn the screw CW to richen the mixture and CCW to lean the mixture. I'm sorry, I don't know which way to turn it to get the duty cycle where you want it but that is easy to figure out once you start adjusting.
I'm sure others can tell you which way to turn the screw to get the duty cycle where you want it.
Paul

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84 500 SEL (307,xxx miles)