should this be checked or not whats teh difference the arap bin is checked my stock apyn bin is not.

Just a WAG but Id guess tahts the option to use the PW vs. LV8 table. Id stick with the MAF calcs. Its better to use teh airflow directly rather then try to estimate the load and base the fueling off of that.

As for the difference, the PW vs. LV8 vs. RPM uses teh load variable to look up the actual pulsewidth needed for the injectors. The maf calcs uses the airflow to calculate the needed injector duty cycle, which is then multiplied by the DRP to get the pulsewidth. Again, this is assuming that Im not mistaken and thats what the table is in your bin.