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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?

ria
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If the injectors are fired electrically(which they most likely are), you could wire in a voltage-switch to the injectors, so that it is closed when the injector is fired. This would allow you to measure the time spent open, and do a little math based on the flow-rate of the injector to get a calculated measurement of the fuel injected into the system. If they're fired mechanically, you could try to make some kind of sensor to read the state of the mechanical system, although that might be a little more interesting/complicated.

Annath
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I also drive a strictly mechanical diesel Mercedes and have been interested in this question for some time. Presumably a measuring device could be fitted in the accessible, low-pressure part of the fuel system, in the neighborhood of the primary fuel filter.

Both mechanical and electrical diesel flow rate meters (flowmeters) do exist; McMaster-Carr sells one of the former, and there are several sources of the latter visible on eBay. In some of the latter, a wiring harness connects the sending unit to a display panel. Probably, the signal from such a system could be hijacked for your Arduino application.

Aaron Brick
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