TwEEcer TB Air Flow question

Discussion in 'Fox 5.0 Mustang Tech' started by fox_bodies_rule, Mar 22, 2007.

  1. Under the scalers tab there is a setting called TB air flow. The stock A9L setting is .55 something. Is it a co-incidence that the stock TB is 55mm? If not, where do you find the correct setting for a 70mm TB (.70?) or is that a function of the MAF voltage output and the TB airflow is what it is and the TB air flow setting is a multiplier factor for the computed actual MAF?
  2. It is coincidence.

    The only way I know to figure out he TB airflow is by datalogging and using the MAF data.

    Not sure on the details though, as I never made it that far in my tune.

    I will look into it some more tonight...
  3. Thanks Jason, this one has me stumped. Time to read the entire EEC-IV manual that you turned me on to I guess.
  4. you need to get the car warmed up, then pull the spout and the IAC while datalogging, the MAF reading that you get then is what you need to put in as the throttle body airflow
  5. I forgot who I got this from, it was a person on Stangnet though. If you read through it, it states how to get the TB air flow. Thanks to the person that wrote it...

    • Adjust the idle screw on the Throttle Body (TB) all the way out allowing the throttle plate to fully close. Now turn the idle screw in just until it touches the mechanical linkage. Finally, turn the idle screw in one full turn. This will place the TB plate at the correct location.

    • Adjust the Throttle Position Sensor (TPS) to .98Vdc using CalCon. You may have to ream out the mounting slots on the TPS in order to achieve .98Vdc. There has been a lot of discussion about what the correct TPS setting should be, but I have found that .98Vdc works fine for me. Note: the voltage reading at the sensor may be different from CalCon’s reading due to line resistance. If the TPS wiring is in good shape, then the voltage difference should be minimal. If there is a significant difference find the bad connector or wiring and fix it before continuing.

    • Unplug the Idle Speed Controller (ISC) so that you can datalog the base idle. Now start the car and datalog the idle RPM and Mass Air Flow (MAF) voltage at normal operating temperatures. After achieving the datalog, calculate an average MAF voltage vrs RPM. For example:

    .8 675

    Plug the ISC back in.

    • Now its time to start entering parameters into CalEdit, but first let me describe how the functions and scalars work that pertain to the ISC. The scalar “Throttle Body Air” is used to tell the EEC how much air in pounds per minute enters the engine through the TB at an idle. The factory uses a 60mm TB and a 55mm MAF with a base idle of 550. The stock combination will produce a MAF voltage of .615 Vdc at 550 RPM. Using the formula (MAF * 2.2046226 / 60 = TB Air Flow) you will see how the factory came up with the numbers they did. For example ( [.615Vdc = 14.969kg/hr] *2.2046226 / 60 = .55005 pounds/minute) will result in the factory setting of .55005. With that in mind, I’m using a 70mm BBK TB and a 73mm C&L meter with a 93 Cobra intake, which produces a MAF voltage of .8 at 650 RPM. Using the formula above and the MAF curve I calculated the new TB airflow. Keep in mind the MAF curve needs to be tuned properly, or this calculation will be wrong. My new TB airflow is ([.8Vdc = 25.357kg/hr] * 2.2046226 /60 = .93). Also keep in mind that every time you adjust the idle that the TB airflow needs to be recalculated.

    • Now the function “ISC Neutral Idle Air Flow” can be adjust to accommodate the new TB airflow. The factory uses .75 air for 672 RPM, thus by subtracting the TB Air Flow you get .2 air at 672 RPM. Here is where I believe people get confused. I have read in many of the forums that the ISC should be about 20 % duty cycle at an idle, but I believe this to be miss leading. If the stock application has .2 air at an idle, as proven above, then by looking at the function “ISC Transfer” you will see that .2 air dictates that .34 or 34% duty cycle is applied. Maybe I’m wrong, but if you now adjust the idle up a little by using the TB set screw then the ISC duty cycle will go down in order to maintain the desired RPM. This is how I believe the 20% duty cycle is possible. The factory Idle is set to 672 with a base of 550, which is a difference of 122 RPM. This difference is what allows the ISC duty cycle to be at 34%. So if you take the desired RPM and lower it, you should see that the duty cycle should also decrease and vise versa. For my set up I entered values into the function “ISC Neutral Idle Air Flow” that corresponded to my new MAF curve.