CLASS RACER FORUM - View Single Post - EFI, Alpha-N vs Speed Density fueling Strategies

pbp1 · 03-10-2014, 02:50 PM

Ricki, Closed loop is a separate consideration.

For those who aren't familiar with the term, Closed Loop is a process where the system compares the actual Air/Fuel ratio read by the O2 sensor to your programmed target A/F ratio and makes corrections to the fueling based on the difference. In Open Loop, the system still reads the Air/Fuel ratio from the O2 sensor but it does not make any corrections.

You can run Alpha-N in Closed Loop or Open Loop and you can run Speed Density mode in Closed Loop or Open Loop.

The compensation I am talking about is not really a correction. In speed density, the air pressure and temperature are taken into account "on the front end" of the ECUs fueling calculations. In Alpha-N mode with FAST systems, there are corrections made in the ECU behind the scenes for Air Pressure as long as you have a MAP sensor plugged into the harness with the hose barb of the sensor open to the atmosphere and an Air Temp sensor plugged in. Even in Open Loop, these corrections are going on behind the scenes without any input from you. If you do not have a MAP sensor or Air Temp sensor in your system, the ECU just assumes standard temp and pressure and you are using the system like a mechanical carburetor of mechanical injection.

03-10-2014, 02:50 PM	#16
pbp1 Junior Member Join Date: Mar 2013 Posts: 78 Likes: 11 Liked 18 Times in 5 Posts	Re: EFI, Alpha-N vs Speed Density fueling Strategies Ricki, Closed loop is a separate consideration. For those who aren't familiar with the term, Closed Loop is a process where the system compares the actual Air/Fuel ratio read by the O2 sensor to your programmed target A/F ratio and makes corrections to the fueling based on the difference. In Open Loop, the system still reads the Air/Fuel ratio from the O2 sensor but it does not make any corrections. You can run Alpha-N in Closed Loop or Open Loop and you can run Speed Density mode in Closed Loop or Open Loop. The compensation I am talking about is not really a correction. In speed density, the air pressure and temperature are taken into account "on the front end" of the ECUs fueling calculations. In Alpha-N mode with FAST systems, there are corrections made in the ECU behind the scenes for Air Pressure as long as you have a MAP sensor plugged into the harness with the hose barb of the sensor open to the atmosphere and an Air Temp sensor plugged in. Even in Open Loop, these corrections are going on behind the scenes without any input from you. If you do not have a MAP sensor or Air Temp sensor in your system, the ECU just assumes standard temp and pressure and you are using the system like a mechanical carburetor of mechanical injection.