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Momentary Rich AFR when lifting off gas pedal


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Good day Sirs, i have a Honda B16 NA engine. everytime i let off the gas pedal, AFR goes as rich as 9.5 before coming back to Idle AFR of 14.7 approximately. The duration it stays on rich AFR before returning to normal coincides with the duration delay i set for Fuel overrun fuel cut (Tq reduction / introduction time), which is currently set to 2seconds.

While i understood having a rich AFR for a split second doesnt hurt, i am curious to see if theres any adjustability for this part.

*I tuned it for 2 second delay for torque reduction because somehow it gave me better drivabilty when shifting gear and decelerating. Tried reducing to 1 second or zero delay, the car was jerky whenever throttle was let off.

Any info would be very much appreciated :) Have a great day guys!!


16Jan23 updated fuel.pclr drivability check log.llg

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This is pretty normal and not much you can do about it.  This is due to two factors - 1 is your fuel is injected into the port on the cycle prior to induction.  So you have the correct amount of fuel sitting in your intake port for the amount of air that was ingested last cycle, but if you suddenly close the throttle then you have a lot less air going in for the amount of fuel that has already been injected.  The second factor is "wall wetting" of "fuel film", there is always a significant volume of fuel "clinging to the ports walls - not being burnt - when you suddenly close the throttle you get higher vacuum in the port which evaporates more of that fuel film that was previously sitting there not being combusted. 

Since in both cases the fuel was already sitting in the port, there is not much the ecu can do to correct it.  Some ecu's have a "deceleration enleanment" type function (basically opposite of accel enrichment) which can help it "catch up" quicker, but you will always have that initial rich spike.  

Having said that, yours looks like it sits rich in overrun for longer than normal though so you probably need smaller values in the overrun area of your fuel table.  Possibly add another row at -80kpa to get rid of any interpolation with the -70row which is possibly passed through at light cruise. 

The 2 sec delay on ORFC is not unusual.   

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