Was wondering if anyone has ever installed a fuel flow meter to monitor how much fuel the engine pulls while driving.

Of course placement of the sensor is an issue.
Correct me if i'm wrong; depending on which car you apply this to, some cars having a closed loop fuel system and some have an open loop fuel system? One with a return fuel line would be an open loop fuel system? And a closed loop would be like an engine that just drew fuel as needed.

An open loop fuel system, the sensor could not go on the main fuel line from the tank because excess is always going back to the tank. Maybe if you put it inline to one of the injectors?

Also you would have to have the correct senor (ie sensitivity, max flow, min flow, no interactions with diesel or gasoline depending on what car you put it on).

Then you would have a gauge in the cockpit and as you drive, you see how fast you can go, while drawing the least amount of fuel. Is thier any fallacy in my logic?

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'80 240D (sold) wish I didn't.
'85 300D (240K miles)