Engine shutdown / power off

[Eric S]

Been doing some back-to-back comparison between G4X and factory ECU on MX-5; mainly figuring out the idle air valve frequency and cold start behaviour.

With G4X, the engine shutdown by turning the key from ON to ACC (or OFF) makes the engine shake and feels like the sparks want to fire (doesn't feel like a smooth shutdown compared to factory ECU, where I don't feel the engine shake at all when shutting down).

It essentially cuts 12V to the ECU when key is turned away from ON and there's no dedicated digital input that tells the ECU 'I want to turn off the engine'.

Is there something that can be done to allow more smooth shutdown?

[Adamw]

57 minutes ago, Eric S said:

It essentially cuts 12V to the ECU when key is turned away from ON and there's no dedicated digital input that tells the ECU 'I want to turn off the engine'.

The ECU does not need to do anything special because as soon as you turn off the ignition, you have disconnected power from the injectors and ignition coils.  Even if the ecu did stay alive for a few milliseconds it cant physically inject any fuel or make a spark if the injectors and coils have no power.  

Im suspicious there may be some other difference - maybe injector timing, idle mixture or idle valve position that means there maybe just enough mixure remaining in the port for one more cycle after shutdown?