Did you try working on the source of the offending RF, i.e. capacitors on the fuel pump power leads, as close to the fuel pump as you can get them? Try grounding the fuel pump at a different spot on the chassis - or at multiple spots. Fuel lines are typically isolated from the chassis with plastic retainer clips. The RFI might be radiating from the fuel line itself; try grounding it to the chassis at a couple points on its run from the tank to the motor.
RFI can be a royal PITA to cure...
We work together every damn day. --Jon Stewart