Just a thought but if you can get 2 fuel flow sensors you can get a pretty accurate reading. You have to get the flow in and out of the system and then just do a little subtraction. Can't remember where I saw it. But someone did this and it worked over all driving conditions. If you have a flow of 5 gallons per hour(GPH) in and 3GPH out then you are using 2GPH. Or what ever measure you use. You get the in and out because the injection system has a return line to the tank for the fuel not used. Only problem with this is trying to find the flow sensor. I have been trying to find just one for my old truck and they seem to be non-existent now. They used to be every where.