This is a Mercedes-Benz 308D van, year 1992, model 602.316. Pre-OBD, no electronics of any sort, everything is purely mechanical.
I would like to retrofit a system which would measure the precise amount of fuel injected into the engine in real time, to be able to feed the data into my Arduino and log it there.
The engine is an OM601.940 - a classic plain naturally-aspirated diesel engine (neither turbocharged nor supercharged). Fuel injection is indirect via a prechamber arrangement. The injection pump is a mechanical fuel injection unit with a 5150 ±50 RPM mechanical governor, automatic altitude compensation, and a 'load sensing' automatic idle speed control.
How could I make a device to precisely (sort of ±1%) measure the amount of fuel going into the engine in each injection and feed the data in real time to an Arduino micro-controller board to be processed there?