so I've got an Tecumseh engine that's just laying around, without any use, and it does fine.
The other day, I got an idea to try converting it to a basic EFI system (with basic I mean that all I need to make it run, nothing too precise, like including throttle position sensor, MAP sensor... just some basic function of making an injector shoot depending on if there is air flowing and if the crank is at the right spot).
Basically, would make it just for a showcase, just to make it work, somehow, as I mentioned above, no serious calculations whatsoever.
- A basic optocoupler/optointerrupter/optical element, placed on top of the engine, just where the magneto coil is located, and would but an additional shaft on the fylwheel where the second magnet is located, so when it spins, and the shaft goes through the sensor, it would send a signal to the Arduino noting that the crankshaft is at a given position (needed for knowing when the valves are opened or closed, later used to know when you need to shoot fuel into the intake).
- Next off, I'd need a MAF sensor (Mass Air Flow) for detecting when the air is being sucked into the cylinder (needed since just a signal from the optocoupler won't do because the flywheel makes 2 full turns while the fuel is being sucked in just once, shortly said, bad timing).
- Next just a basic fuel injector, would be placed at the very end of the intake, closest possible to the valve. Would drill a hole through the intake, and hold the injector in place with some high-temperature silicone glue. The arduino would control the firing pulse (likely with a transistor, since most injectors are fed with 12V).
That's the most basic you can go, and that's all I really need, there are more elements for high precision but meh.
Generally, I'd pull the guts out of the old carburetor, and just leave a free flowing empty tube just for the airflow. Since injectors need some preassure, I'll just pressurize a gas tank with an air compressor to get somekind of preassure at least.
So, what's the issue?
The issue in all of this is that I'm dealing with a small engine, and there are NO MAF sensors for such ammount of small airflow, and I don't really need anything precise, just to make sure I can get basic logic (basic as in terms of 1- there is airflow, 0- there isn't airflow (just for now)), but I can't find any that small, since I expect that most would read nothing to 0.00001.
We could also count a too large injector making an extremly unbalanced mixture, so bad that the motor won't even run at all, but that's a smaller issue.
So, does anyone have any solution? Is there a different way of knowing the airflow, something DIY-like (since the MAF sensor is just a wire, and letting current through it heats it up, and the airflow would cool it down, and the difference in temperature results in different current and so on...). Did somebody here try to something like this. Can't really find anything online for such projects.
Thanks in advance!