I would always put the fuel filter in front of the pump. If you don't then you run the risk of small aluminum shaving getting stuck in the pump and ruining it (as me how I know). Some people even run two filters, one in each wing root to filter before the selector. You want to trap the junk that comes out of the tanks as quickly as possible so it doesn't have a chance to get into any of your items down stream, including the pump and fuel flow sensor. It is amazing how much stuff comes out of the tank during the first 100 hours of flying. I have my sensor mounted on the engine side of the firewall with a 90 degree bulkhead fitting thru the firewall, then about a 4 inch straight before the sensor, and a flex line from the sensor to the fuel servo (injected engine). So my sequence is: selector, filter, pump, fuel flow sensor.
In some of the older engine monitors, there was no way to calibrate a fuel flow sensor, so people really had to mess around with sensor location in order to try to get it reasonably accurate. That is where the urban legend of 6 inches before and after comes from. Since Dynon allows you to adjust the "K" factor, sensor position is not that critical. Once initially calibrated, my fuel totalizer is accurate to 0.1 gallons per 38 gal tank. There are two other RVs flying with Dynon systems in my row of hangers, both have the sensor mounted on the firewall after the filter and pump (in that order) and both have the same accuracy as mine once the did the calibration.
Best of Luck and enjoy your plane,
Regards,
Mel Jordan
RV-6A, Tucson
