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]

I've thought through the same thing, it should be possible, I lacked the skills to implement, though I've been working on that! I assume the lookup table would encompass the full-load enrichment function, too? If you can mock up a prototype I can test it on my simulator and do a direct comparison to a stock MPS.

You could test the theory.
Do you have an arbitrary function generator?
If you can configure it for:
Single pulse, adjustable duration squarewave.
Amplitude 1.0VDC, Offset -1.0VDC
Negative going pulse
External trigger input connected to 'TL Trigger' (input excitation signal into MPS)

Connect waveform output to MPS Output to ECU


Now test the system while varying pulse durations on the arb gen, and you should be able to control the injector pulse duration just like adjusting the vacuum on your MPS vacuum pump

stugray, which pressure sensor are you thinking of using? I2C or 1-wire? I could also give your design a try.

I just grabbed something simple off of ebay that I could actually find the datasheet for (or thought I could...)
I ended up with a Denso TN079800-3280 5V PS-30
I also found a small DC-DC converter from Digikey for the neg DC voltage.

If the experiment above with the -1.0VDC pulse works and we don't need to simulate some funky waveform, then an Op-amp wouldn't be required and we could just use an opto to pull down to the neg DC rail for the output signal.

If you really want to experiment, I could send you the MAP sensor, an arduino beetle, the DC-DC converter, some 1-wire temp sensors, and I even have some high speed optos laying around.

[pbanders]

I've thought through the same thing, it should be possible, I lacked the skills to implement, though I've been working on that! I assume the lookup table would encompass the full-load enrichment function, too? If you can mock up a prototype I can test it on my simulator and do a direct comparison to a stock MPS.

You could test the theory.
Do you have an arbitrary function generator?
If you can configure it for:
Single pulse, adjustable duration squarewave.
Amplitude 1.0VDC, Offset -1.0VDC
Negative going pulse
External trigger input connected to 'TL Trigger' (input excitation signal into MPS)

Connect waveform output to MPS Output to ECU


Now test the system while varying pulse durations on the arb gen, and you should be able to control the injector pulse duration just like adjusting the vacuum on your MPS vacuum pump

stugray, which pressure sensor are you thinking of using? I2C or 1-wire? I could also give your design a try.

I just grabbed something simple off of ebay that I could actually find the datasheet for (or thought I could...)
I ended up with a Denso TN079800-3280 5V PS-30
I also found a small DC-DC converter from Digikey for the neg DC voltage.

If the experiment above with the -1.0VDC pulse works and we don't need to simulate some funky waveform, then an Op-amp wouldn't be required and we could just use an opto to pull down to the neg DC rail for the output signal.

If you really want to experiment, I could send you the MAP sensor, an arduino beetle, the DC-DC converter, some 1-wire temp sensors, and I even have some high speed optos laying around.

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.