Fuel Pulse Width

I got my dev board measuring the fuel pulse width today.
Here's a quick pic of pulse width against rpm and afm volts:

More details to follow when I've had time for some more investigation...

Stock Rev Limit

I started looking at the fuelling on the stock ECU today.
The first thing I did was look at where the RPM limit was.

It looks like the ECU stops injecting fuel above 7197 RPM, and doesn't start injecting fuel again until the revs drop below 6935 RPM.

Stock Ignition Map Continued

I've been doing some more work extracting the stock ignition map.
I've tried changing ECT and IAT temperature, enabling/disabling TEN, and playing with the WOT and closed throttle switches.
So far the only thing that seems to affect the timing is whether the closed throttle switch is shorted to GND or not.

Closed throttle ignition timing:

Open throttle ignition timing:

The data can be downloaded here and here.

Idle Valve Drive

Just had a quick look at the idle speed output.
With TEN shorted to GND it outputs a fixed 160Hz PWM with a negative width of ~2.6ms and a positive witdh of ~3.6ms.
It seems unaffected by AFM voltage and RPM.
At some point I'll look at what it does when TEN isn't enabled.

First attempt at extracting the stock Ignition Map

I've been doing some more fiddling with the stock ECU and can now control the RPM and AFM voltage going into it, and measure the spark angle coming out (using my STM dev board).

I wrote a little bit of code that steps the RPM and AFM voltage and spits the spark angle out of the UART.
I logged the UART data and inserted it into Excel and managed to produce this:

As before I've currently got TEN shorted to GND, and a fixed resistor for IAT (2k) and ECT (330R), and closed/wide-open throttle inputs left open.

Note that I've added 10 degrees to the angles to account for the stock static 10 degree offset.

I'll publish the raw data once I've done some more work and confirmed what I'm doing and what I think I'm measuring are correct.

One more note whilst I'm thinking about it - The ECU logs an error when the AFM voltage drops to 0.2V or lower.

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Update: Although the static timing is set at 10 degree on the MX5, I've just been looking at the spark outputs again - at idle with TEN and closed throttle shorted to GND (the conditions under which static timing is set on the engine)  the spark triggers at 3 degrees before the falling edge of the crank signal.
So, rather than being at -10 degrees, I think the falling edge of the crank signal is probably more like -7 degrees.
Though given that people often increase the advance by 2 to 4 degrees on the 1.6 engine my additional 10 degrees advance is probably about right!

ECT and IAT Calibration

Some notes on the ECT (engine coolant temp) and IAT (intake air temp) sensors.
The following is info I've googled, so I don't know if it's accurate or not...
The voltage is calculated from the 'googled' temp/resistance values based on the 2k7/5V pull-up in the stock ECU.

Temperature, Resistance, Voltage
-20, 16150, 4.28
 40,  1150, 1.49
 80,  330, 0.545

ToDo: Update with some better data when I've found it.

CAS Signals

Just some notes on the CAS signals.

Apparently this is from the service manual of a mitsubishi 4g18 engine (which uses the same CAS as an NA)
I believe it's advanced by another 2 degrees on the MX5 though:

Some more info I found on the CAS timing signals:

The numbers are crank degrees relative to the #1 TDCC (negative being before and positive after)

crank signal (CKP) edges in one engine cycle (8 edges total):

raising edge at -80
falling edge at -10
raising edge at 100
falling edge at 170
raising edge at 280
falling edge at 350
raising edge at 460
falling edge at 530

cam sync signal (CMP) edges in one engine cycle:

raising edge at -95
falling edge at 48
raising edge at 265
falling edge at 335