Asynchronous Injection

[mike2016]

i don't fully understand the logic of this setting.

for example in this log, in the latter part of the log starting around 3:10

when there's a sudden throttle change, lambda goes way too lean. 

Is this due to lag of the lambda sensor, or should i increase the async injection time? 

[Adamw]

Normal scheduled fuel injection is synchronous - that is it only gets injected once at a fixed point in the engine cycle (usually finishing around 400deg BTDC, so a long time before combustion).  So if you only have synchronous injection (like most ecus) and you suddenly stand on the throttle after the injection event has already finished, then the next combustion event will be lean because you only originally added enough fuel for the amount of air that was flowing at the time of injection.  

With Asynchrous injection the ecu is always watching the fuel calculation even after the injection event, so if there is a sudden change in airflow after the main injection has finished, then ecu will add extra injection events to "top up" the fuel that is already sitting in the port waiting to be inhaled.

The minimum async injection setting is only used to prevent the async from reactivating too often when there is only a small amount of extra fuel calculated.  I suspect the main thing that influences what is a good minimum setting is your injector size.  Probably around 1.0ms would be suitable for typical ~500cc injectors, and maybe 0.5ms for ~1000cc injectors.  All my cars started with 0.5ms in there and it seems to work good so I havent experimented with it much further.

Your little lean spike could be not ernough accel fuel or the min async is too big.  You really need to look at what was happening to accel fuel at the same time.  Also, dont be too concerned about getting a dead flat lambda, there are all sorts of interactions going on during heavy transients and measured lambda is not always a good indication of how well it is all working.  Aim for best response rather than flatest lambda.  

  

  

 

[mike2016]

Well explained. Thanks Adam.