I'm not an expert but my Mach 1 is running on e85 out of the pump, and I hooked up my AEM Eugo AFR guage and 02 sensor.

The car seems happiest at around 8:1 AFR.

Most guides for forced induction say to start tuning on E85 at around 7:1 AFR, and try leaner from there.

Being way too lean may have contributed to your heavy detonation