10-16-2009, 02:07 PM
A car has parameteres for Open and Closed Loop mode such as engine temperature, engine speed, load (which is a calculation NOT REAL), and a multitude of different things for different cars.
First a quick refresher for those who dont know much about these terms Open and closed loop mode.
Your vehicle at idle, light load, and cruising is in what we call closed loop mode. This is where the ECM is monitoring your Oxygen Sensor as it swings back and forth to create the "optimum" AFR of 14.7. It also has to be at a certain temperature range etc etc. When it operates outside this range, letsss say you hit the gas, the ECM now ignores the oxygen sesnsor and looks to Intake Temperature, MAF Hertz, or MAP readings and "chooses" a certain map (tuning is actually 3 dimensions, this is why tuning is very hard when you get REALLLY picky, as it is not just a simple table, and there are a million variables).
Based on the pre-loaded table it has chosen, it will set a "target" AFR that is simply a calculation already built into the ECU based on those variables along with the volumetric efficiency of an engine. Scotty's table is those "targets" and I use that very loosely. This is Open Loop.
All the 14.7 is closed loop mode, (ps if you wanted to pick back up gas mileage, you could lean burn your closed loop mode), as you can see as "load" increases there is a certain point where it drops out of closed loop mode. Same with this rpms. Now you look at highway, and depending on how fast he is going, and wether it is a hill or descent or smooth will increase or decrease load. He has now changed the parameters for when the car enters closed loop mode, now it is open loop for "more time" and the possibklity of being in open loop during "highway cruise loads". Thats why he will be seeing a decrease in gas mileage.
First a quick refresher for those who dont know much about these terms Open and closed loop mode.
Your vehicle at idle, light load, and cruising is in what we call closed loop mode. This is where the ECM is monitoring your Oxygen Sensor as it swings back and forth to create the "optimum" AFR of 14.7. It also has to be at a certain temperature range etc etc. When it operates outside this range, letsss say you hit the gas, the ECM now ignores the oxygen sesnsor and looks to Intake Temperature, MAF Hertz, or MAP readings and "chooses" a certain map (tuning is actually 3 dimensions, this is why tuning is very hard when you get REALLLY picky, as it is not just a simple table, and there are a million variables).
Based on the pre-loaded table it has chosen, it will set a "target" AFR that is simply a calculation already built into the ECU based on those variables along with the volumetric efficiency of an engine. Scotty's table is those "targets" and I use that very loosely. This is Open Loop.
All the 14.7 is closed loop mode, (ps if you wanted to pick back up gas mileage, you could lean burn your closed loop mode), as you can see as "load" increases there is a certain point where it drops out of closed loop mode. Same with this rpms. Now you look at highway, and depending on how fast he is going, and wether it is a hill or descent or smooth will increase or decrease load. He has now changed the parameters for when the car enters closed loop mode, now it is open loop for "more time" and the possibklity of being in open loop during "highway cruise loads". Thats why he will be seeing a decrease in gas mileage.
2020 Ford Raptor
2009 Z06
1986.5 Porsche 928S
2009 Z06
1986.5 Porsche 928S