D-Jet Bench Setup, Let the experimenting begin (again).... Options

[pbanders]

See attached photo, this is my D-Jet bench setup. The black box on the left is an EFI Associates 1400 D-Jet tester (circa 1972) that measures the injection pulse width, simulates the trigger contact points over a range of engine RPM's, and provides reference values for the CHT and air temp sensors, as well as the throttle switch operation. The ECU is an 044 that I've used in the past for all of the oscilloscope traces on my web page, I can access any circuit in the ECU with it. I've got a TPS connected to the harness in the middle of the picture, as you turn it it you can watch the injection pulse width increase, then when you stop, you can see the pulse with relax back down (there's a delayed effect as well as an immediate effect). I have an air temp sensor plugged into the harness, and instead of a CHT, I have a variable resistor (half of a pot) that lets me simulate the engine temperature. That's a NOS 043 MPS in the upper right, with my vacuum pump attached to simulate engine load.

I've also got an interposer box that I can put between the ECU and the wiring harness that can be installed into the car so I can monitor all of the ECU pin connectors while driving the car. My current box is a PITA to use in the car, my old design sucks. I've got an idea for a better one that I'm going to have to build.

I've also got a Fluke calibrated pressure sensor that I can independently monitor the manifold pressure, or the pressure at any other point in the vacuum system. I can datalog the output from my DMM to get any of the pressure values as a function of time.

Now, just gotta do something useful with it all. BTW, working on the 914 is one of about a million things I'm trying to do simultaneously, so I tend to get to it irregularly, just hoping that's more than "never". I plan to look into the hot start problem first. I'm going to take some data when it happens on the car (i.e. measure the voltage at the CHT through the sequence of events), bench simulate it, then try to come up with some simple solutions. The idle stabilizer will take longer to do.

[stugray]

Out riding my bike and thinking - digital pressure sensor probably won't be fast enough, probably have to use an analog automotive sensor and sample it at about a 1 ms rate.

I don't think we would need to sample the MPS and the air intake temp that fast, maybe 10 Hz?
Then throw in some digital filtering (average) in software and you would have less than a few tenths of a second latency.
I'd have to play with the MAP and an oscope on a real engine to know how fast it even responds.

You wouldn't even sample the input trigger, it would operate on a input channel event trigger (arduino attachInterrupt()).
So every time the subroutine is called by the input trigger (TL goes low) it:
drives the SC_IM_bias output signal to -1.0V. (or some negative voltage TBD by experiment).
latch a system time (start_of_pulse)
Read the time averaged MAP value (MAP)
Read the time averaged Input temp sensor reading (IAT)
Using those two values, lookup a pulsewidth from a lookup table (pulsew)

set the timer in the future for start_of_pulse + pulsew
exit from interrupt routine

When the timer goes off:
drive signal SC_IM_bias output signal to 0.0V
ECU stops the injector pulse.

This subroutine would run every time the TL input signal goes low

In the "downtime" between the subroutine running, it would collect & average the MAP & Temp sensor data.

If you send the stuff to me, I can't tell you when I'd get around to it. You'd be better off doing it and I could test it out if you want, unless you have everything you need to verify it. re: Denso sensor - yeah, that's what's needed. As for the proof of concept, I don't have an arbitrary function generator but could probably do a circuit with a 555 or two that could do the function you describe.

What sampling rate does the megasquirt use? I'm figuring this would need to be about on the same order.

You absolutely could do this as proof of concept with a 555 in monostable mode.
Hookup a +/-5VDC power supply and use the 555 to drive a opto/mosfet to pull the test signal up & down