WR450F 2012 AFR while cracking throttle at idle


To find out why people find better hot starting when slightly cracking the throttle



Engine warmed up well (right radiator 100% blocked by sheet of paper).

PowerTuner maps both all zeroes.

Euro-header and muffler, fitted with APSX WideBand O² sensor kit (Bosch LSU4.2)

WideBand sensor has been calibrated according. to spec.



(you need very good ears to hear when rpms are about to rise)




Well, not very convincing. One can see that when I start to open the throttle,

right BEFORE rpms are rising, the AFR jumps slightly to the right (e.g. lean).

As soon as rpms ramp up the ECU switches to the rather rich PowerTuner mixture.



At 3000 rpms we're already spot on the lowest rpm value of the Powertuner mapping,

hence at 3000 the mixture is only governed by PT fuel map and not CO setting.

The transition betewen (low ~1600) idle rpm towards higher rpms, due to slightly cracking the throttle,

does show an ever so slight leaning of the mixture but only until the ECU "sees" the higher rpms.

This is not a valid simulation of "engine-start-w-cracked-throttle",

as the rpms are already past "cranking-rpms"



It could very well be that in "cranking mode" (e.g. until the ECU "sees" the elevated rpms of a running engine)

the mixture stays leaner then with fully closed throttle. 

That might be why starting an engine that is configured to idle rather rich (stock)

is helped by cracking the throttle slightly.


(Of course I still do advocate to get the CO setting right,

 then that cracking is unnecessary, as it is on my bike)



I'm still running CO at -30, and never every seen a lean idle condition indicated.

Edited by WRF-Rowdy

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