Sometimes On CNG They Try To Bypass Fuel Pump With Some Switch That It activates On Petrol Switch Side And Deactivate On CNG side
Getting To This They Cut And Route Some wires Via Switch ..So Check That Also....
Fuel Pump Is Wired To ECU Getting Fp Signal From ECU Which Activates Fuel Pump Relay When You Crank .....!!
Also Check If Your Relay Is Working All Fine And Good ..
Also Check For Fuel pump Ground Connection.....All These Should Be Checked In Order To Keep Fuel Pump Working Nicely (Wiring Side)
Routing Fuel Pump Main Supply Wire Via Some Switch Can Also Be Reason As Switch May Not Be Of Proper Amp Rating And Heatup