Stock ECU decel fuel cut?

[armstrom]

I'm pretty new to the FRS/BRZ/86 community but I've had fairly extensive experience with tuning older cars (MR2 turbo mostly). Most ECUs make heavy use of deceleration fuel cut (Overrun fuel cut) to save fuel and increase engine braking but I've noticed that my BRZ direct injector noise seems to remain the same even under heavy engine braking. I'm just curious if anyone can describe how the decel fuel cut functions on the stock ECU... Are the DI's always firing? I've also looked at some of the stock maps in RomRaider and noticed a map for DI fuel pressure targets, is the fuel pressure variable? How is it controlled?

Thanks!

-Matt

[Mr Nerd]

I don't know the full details but it is apparent that at least in 1st and 2nd gear it does not cut off fuel entirely on decel. You can confirm this by looking at your instant MPG calculation display on the dash. When decel in 1st and 2nd gear it will never reach anywhere close to the meters limit (127mpg). From my experience it never goes above 10mpgs while decel in 1st gear.

[steve99]

Originally Posted by armstrom

I'm pretty new to the FRS/BRZ/86 community but I've had fairly extensive experience with tuning older cars (MR2 turbo mostly). Most ECUs make heavy use of deceleration fuel cut (Overrun fuel cut) to save fuel and increase engine braking but I've noticed that my BRZ direct injector noise seems to remain the same even under heavy engine braking. I'm just curious if anyone can describe how the decel fuel cut functions on the stock ECU... Are the DI's always firing? I've also looked at some of the stock maps in RomRaider and noticed a map for DI fuel pressure targets, is the fuel pressure variable? How is it controlled?

Thanks!

-Matt

have a look in Romraider at the "over run fuelling " tables there about 4, they are related to load and rpm. At low loads on overrun above certain rpm limits injectors are shut off.


log the port and direct injector pulse widths


Fuel pressure is variable to the DI system and controlled by ECU.


Increasing these pressure multiplier was how the oft guys added the 30% extra fuelling required for E85, in conjunction with adjusting the PI injector scalar.

[Kodename47]

Originally Posted by steve99

Fuel pressure is variable to the DI system and controlled by ECU.

Increasing these pressure targets was how the oft guys added the 30% extra fuelling required for E85, in conjunction with adjusting the PI injector scalar.

Don't confuse DI Pressure Targets and Pressure Multipliers. The 2 do very different things. DI pressure targets change the pressure in the fuel rail, where the limits are the physical pump. The pressure multipliers adjust the injector open time according to the fuel pressure.

OFT does not change the DI pressure targets. It adjusts the pressure multipliers.

[steve99]

Originally Posted by Kodename47

Don't confuse DI Pressure Targets and Pressure Multipliers. The 2 do very different things. DI pressure targets change the pressure in the fuel rail, where the limits are the physical pump. The pressure multipliers adjust the injector open time according to the fuel pressure.

OFT does not change the DI pressure targets. It adjusts the pressure multipliers.

haha yes ill fix it up

[armstrom]

Thank you all for the great responses. I need to see if I can dig up the stock definitions for my ECU and do some datalogging.
-Matt

[Wayno]

MY16 AU MT (F20P) I saw today has different overrun values than every other car, even 2016 cars in other markets.

Note:
- A and B are likely counterparts somehow.
- MY16 values seem to be richer at high rpm, not leaner, particularly in the B table.

[Mr Nerd]

Originally Posted by Wayno

MY16 AU MT (F20P) I saw today has different overrun values than every other car, even 2016 cars in other markets.

Note:
- A and B are likely counterparts somehow.
- MY16 values seem to be richer at high rpm, not leaner, particularly in the B table.

English please?

[Wayno]

Originally Posted by Mr Nerd

English please?

Manners please?