Fuel Economy, Hypermiling, EcoModding News and Forum - EcoModder.com - View Single Post - How do you get engine braking with fuel use? Timing Retard?

Michaelflat1 · 12-30-2020, 01:36 PM

I drive an electronic throttle car, and unfortunately below 1500rpm, if you come off throttle, there will be no fuelcut, if you come completely off throttle, TorquePro shows timing going quite retarded, (maybe -12 degrees) and there is still quite a substantial engine braking effect

At the lowest possible throttle position (quite easy to do on an electronic throttle) i can have the same fuel use, and throttle position, but with +21 degrees advance, and a small amount of torque from the engine, an improvement from negative.

The fuel use parameter in Torque is not always accurate (it is during warmup), but is skewed with EGR operation, as Torque assumes all airflow is fresh air and does fuel use based on that (i believe)

So, in these off throttle events, what is going on? Fuel being kept around stoch mixture (14.7:1 AFR) at/near the minimum throttle position? Is the timing purely to reduce torque to a minimum? Or is the mixture going lean and this is because of knock concerns? At roughly 1400rpm off throttle, Torque Pro shows fuel use to be roughly double that of idle, despite the engine producing negative/no torque.

I know that in fuelcut operation (openloop, -15 timing), the EGR and throttlebody are commanded to let some extra air through, and increase manifold air pressure (reducing effective vacuum)
and coming out of fuelcut, the throttle closes and pressure decreases.

12-30-2020, 01:36 PM	#1 (permalink)
Michaelflat1 2003 PD130 Seat Ibiza Join Date: Oct 2020 Location: Essex, United Kingdom Posts: 16 Honda Jazz - '07 Honda Jazz SE Thanks: 1 Thanked 5 Times in 5 Posts	How do you get engine braking with fuel use? Timing Retard? I drive an electronic throttle car, and unfortunately below 1500rpm, if you come off throttle, there will be no fuelcut, if you come completely off throttle, TorquePro shows timing going quite retarded, (maybe -12 degrees) and there is still quite a substantial engine braking effect At the lowest possible throttle position (quite easy to do on an electronic throttle) i can have the same fuel use, and throttle position, but with +21 degrees advance, and a small amount of torque from the engine, an improvement from negative. The fuel use parameter in Torque is not always accurate (it is during warmup), but is skewed with EGR operation, as Torque assumes all airflow is fresh air and does fuel use based on that (i believe) So, in these off throttle events, what is going on? Fuel being kept around stoch mixture (14.7:1 AFR) at/near the minimum throttle position? Is the timing purely to reduce torque to a minimum? Or is the mixture going lean and this is because of knock concerns? At roughly 1400rpm off throttle, Torque Pro shows fuel use to be roughly double that of idle, despite the engine producing negative/no torque. I know that in fuelcut operation (openloop, -15 timing), the EGR and throttlebody are commanded to let some extra air through, and increase manifold air pressure (reducing effective vacuum) and coming out of fuelcut, the throttle closes and pressure decreases.