IDC during Coast-down

[belize1334]

This came up in another thread but I thought I'd continue the conversation here and avoid taking the other one even further off-topic.

The question is, what is the appropriate behavior of the injectors at throttle-lift.

Datalogs on my own car suggest that the injectors drop to about 1.5ms and hang there for about a second before going to 0ms for the remainder of the coast-down. It has been suggested that they're actually supposed to drop immediately to 0ms as soon as the throttle is lifted.

If you have observed one behavior or the other in your own vehicle or if you have advanced knowledge of the ECU code then please chime in.

 

There is a coolant-based map in the code that determines at what rpm the injectors cut back IN. If I recall, they should turn back on at ~1200 rpm stock. Does yours do that?

 

[belize1334]

I'm not sure when mine kicks back in. I've never datalogged that range because I've never had issues with idling/stalling. My concern is more about when/if the injectors are supposed to shut down at high(ish) rpm when the tps goes low and the idle switch triggers.

Here's an excel plot of a recent log.




Note that I have rescaled things so that everything is visible on the same plot. At about 10psi, 3krpm I abruptly release the throttle and engage the clutch. The airflow quickly drops (not pictured) but the injectors don't shut off. They go to about ~1.5ms and hang there for just under a second. They then shut down and I can feel the car "settle" as the engine braking increases. It's this second of continued fueling that has me concerned and it has been suggested that maybe it's not supposed to do that.

 

[belize1334]

C'mon... nobody has ever logged their injectors while shifting or immediately after throttle-lift? Help me out here.