Following Diesel62's suggestion I went looking for a PC scope. I was not able to afford the real deal but was able to find a free ware PC based scope and signal generator.
This is good enough for what I need. A signal generator to simulate an ignition trigger signal and crankcase pressure wave from 1,000 to 13,000 RPM, 16 to 220 Hz. I can use the signal generator to simulate my engine while developing the Arduino program.
The EngMod 2T simulations show crankcase pressure traces from 5-100% throttle and interestingly all the peaks are at the same crank angle.
Because the MAP sensor is slow compared to the short time available Flettner suggested, instead of making a continuous pressure measurement to find the high and low point like I have been trying to do. Just make one or two at the critical points.
Flettners suggestion looks like a great idea.
As I am only looking for the relative difference between the High and Low pressure points then I could just chose an arbitrary low point and compare the relative magnitudes of the peaks from there. That would be a reliable indication of changes in air flow and only one measurement per cycle would be required, much easier.
The Ecotrons 2T EFI software has the VE map (RPM vis MAP) disabled and only allows for an Alpha-N map (RPM vis TPS) and this is totally useless for variable changes in airflow at the same RPM/TPS points on the Alpha-N map.
So I also need a 4T style VE map (RPM vis MAP) as the MAP indicates variations in airflow. But I have so far been unable to persuade Ecotrons to enable the VE map in my tuning software, "Because they don't recommend it". They might be great at writing software code but I am not sure they are 2T experts.
I was talking with Marsheng today and he suggested that if I can't use the MAP input on a VE table to indicate the reduced airflow then I could use the TPS input on the Alpa-N table. The idea is to indicate an artificially low TPS for the actual throttle position when I wanted to tell the EFI CPU that the air flow was momentarily reduced.
Makes sense, get the Arduino to read the TPS signal and the crankcase pressure and then simulate a reduced TPS value for the EFI CPU when the peak crankcase pressure is reduced because of reduced airflow due to reduced wave energy in the expansion chamber.
This way we can have a full normal TPS signal when the motor is on song and the pipe is strongly sucking air through the motor and the TPS signal can be artificially reduced to indicate reduced airflow and fuel requirement when the wave action in the pipe has collapsed and there is less air being drawn through motor.
Brilliant ideas, thanks Diesel62, Flettner and Marsheng.
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