AFM Voltage Range

I've been busy with other projects so my MX5 suff has been simmering on the back burner for a while now...

I did just briefly measure the AFM output voltage on my car though.
So here's a quick note, mainly for my own benefit:

AFM voltage @      0 RPM = 3.95V
AFM voltage @  850 RPM = 3.0V
AFM voltage @ 7000 RPM = 0.8V

IAT voltage @ 28DegC = 2.09V

Fuel Shut-Off on Closed Throttle

Just had a quick look at what the OEM ECU does when the throttle is shut.

If the engine speed is above 2220 RPM, the ECU will stop injecting until it drops to 1900 RPM.

When it does start injecting again the pulse width appears to be increased by ~5ms over the base width whilst throttle is closed.

Injector Pulse Width vs Battery Voltage

Today I have mostly been looking at injector pulse width against battery voltage for the OEM ECU.
It looks like the ECU uses it's 'base' pulse width when the battery voltage is above 16.5V
Below 16.5V the ECU increases the pulse width as the voltage decreases.

Here's the raw data I measured (voltage,pulse width increase in ms):

5, 3.262

6, 3.262

7, 2.912

8, 2.167

9, 1.555

10, 1.156

11, 0.779

12, 0.516

13, 0.357

14, 0.24

15, 0.132

16, 0.048

17, 0

18, 0

19, 0

I also noticed that whilst the ignition advance doesn't appear to be affected by battery voltage, the ignition dwell time is and increases at battery voltage falls.

Ignition During Cranking

Had a quick look at what happens during cranking today.
Couldn't see any affect on the injector outputs, but the ignition outputs were mildly interesting.

Here's one ignition output at 500 rpm normal running (upper trace is crank pulse, lower is ignition output):

And here it is again but with the cranking input driven high:

CAS vs Injector Pulse Relationship

Just a few pics showing the relationship between the CAS signals and the injector outputs on the stock ECU:

The last pic shows the relationship between the crank pulse and the start of the fuel pulse.  Not that the fuel pulse always starts at the same place, around 500-600us after the falling edge of the crank signal, regardless of RPM or load.  The width is varied by changing the end point of the pulse.

Here's a slightly dubious pic of some of the traces stitched together (if only I had a 4-channel scope!):

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.