"Measuring tank" method
What do you need for this method:
1. Calibrated standard measuring tank of the 2nd precision class, 10 liters
2. clean capacities, >10 liters
3. 500-1000 ml capacity measuring flask of the 2nd class with a continuous scale
4. Transparent fuel hoses - 2 pieces.
1. Connect fuel hoses as shown at picture
Supply and return lines will come from tank capacity with some fuel volume inside.
2. Start engine and let it run until both fuel hoses will be fulfilled by fuel. No air bubbles is allowed.
3. Prepare second tank with exactly 10 liters. Attach it to the vehicle tightly.
4. Connect second tank instead of first one. Fuel inside fuel hoses must be saved.
5. Let vehicle perform its usual duties. No pure idling is allowed.
Vehicle must spend some fuel in idle, normal and hard load more (preferably). So you can test flow meter in all operation conditions. Be sure that supply hose fully immersed in fuel and air can't get into fuel system.
6. Stop engine. Remove fuel hoses from measuring tank. Fuel from the hoses must not drop in measuring tank.
7. Measure rest of fuel from measuring tank and calculate fuel consumption. Compare it with fuel meter data.