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maftcalibrationbywbo2

MAFT Calibration by Logged WBO2

The following has been copied from the DSMLink forums. The original (courtesy of Ron Francis) may be found at in this user support forum thread (registered DSMLink users only). The text below has been updated to include 1g-specific info, as well as other minor edits.

Assumptions

  • Zero boost/vacuum leaks
  • You know the correct deadtime and global fuel settings for your injectors, for your car.
  • If you are using recommended injector settings, your base fuel pressure is 43.5psi.
  • You're not over running your fuel pressure regulator.
  • Your fuel system is adequate for your application.

Items to log

  • RPM
  • LTFT-Lo
  • LTFT-Mid (2g) +OR+ LTFT-Hi (1g)
  • STFT
  • WBO2
  • A/F Ratio
  • MAFRaw

MAFT Set-Up

  1. Set MAFT base fuel setting for stock injectors (450's).
  2. Set MAFT idle, mid & WOT knobs to zero.
  3. Clamp IAT/Baro signal in DSMlink under ECU→Miscellaneous.

Idle Tuning (LTFT-Lo) 50hz

  1. Set injector fuel settings to what you were already running them at or what is recommended in the DSMLink guide (or refer to the base injector data page)
  2. While idling the engine watch the LTFT-Lo and STFT.
    • If LTFT-Lo fuel trims are positive, add air at the 50 Hz point in the airflow table.
    • If LTFT-Lo fuel trims are negative, subtract air at the 50 Hz point in the airflow table.
    • Adjust the airflow 1% for each 1% fuel trims are adjusting fuel.

Example: If LTFT-Lo is at a constant +5%, add +5% to the 50 Hz slider in the airflow table. If the LTFT-Lo is at a constant +12.5% and STFT is at +13%, add +26% to the 50 Hz slider in the airflow table. Repeat until you are happy.

Rev Tuning (STFT) 150hz

  1. After you are done with idle tuning, rev the engine and keep it at the 150 Hz level.
  2. Watch your STFT's for needed adjustments.
    • If STFT fuel trims are positive, add air at the 150 Hz point in the airflow table.
    • If STFT fuel trims are negative, subtract air at the 150 Hz point in the airflow table.
    • Adjust the airflow 1% for each 1% fuel trims are adjusting fuel.

Example: If STFT’s are bouncing between +14% and +16%, add +15% to the 150 Hz slider in the airflow table. Repeat until you are happy.

Cruise Tuning (LTFT-Mid +OR+ LTFT-Hi) 250hz

  1. Drive on the freeway at a steady speed to get stable fuel trims.
    • If the fuel trim is positive, add air at the 250 Hz point in the airflow table.
    • If fuel trim is negative, subtract air at the 250 Hz point in the airflow table.
    • Adjust the airflow 1% for each 1% fuel trims are adjusting fuel.

Example: If the fuel trim is at a constant +7%, add +7% to the 250 Hz slider in the airflow table. Repeat until you are happy.

WOT Tuning (A/F Ratio, WBO2, & MAFRaw) 400hz, 800hz, 1200hz, 1600hz, 2000hz, 2400hz

  1. It is easier to do this if A/F Ratio is right above WBO2 in the DSMLink application.
  2. After a 3rd gear pull from 1500rpm to redline study the relationship between A/F Ratio and WBO2 at each MAFRaw Hz point.
  3. Adjust the airflow at each MAFRaw Hz point in the Airflow Table using the associated Hz point in the log.
    • When A/F Ratio is richer than WBO2 add airflow. OR when A/F Ratio is below WBO2 on the graph, add airflow to move A/F Ratio up. OR when you want more fuel, add more airflow.
    • When A/F Ratio is leaner than WBO2 subtract airflow. OR when A/F Ratio is above WBO2 on the graph, subtract airflow to move A/F Ratio down. OR when you want less fuel, subtract airflow.
    • For each 0.10 A/F Ratio is off, adjust by 1% airflow.

Example: You make a pull and you get the following results:

MAFRaw (hz) 400 800 1200 1600 2000 2400
A/F Ratio 9.3 9.5 9.4 9.2 9.3 9.5
WBO2 11.0 12.0 10.7 9.6 9.6 9.4
Adjustment +17% +25% +13% +4% +3% -1%

Note: The following calculation method provides a crude approximation of the needed adjustment and depends on the estimated and measured A/F ratio values being somewhere near 10:1. Use ECMLink's correctly calculated WBFactor value instead.

A simple formula for calculating this is:

(est a/f - WB02) * (-10) = airflow adjustment amount.

Example:
MAFRaw (hz)  800  
A/F Ratio    9.5                               
WBO2 	     12.0                              
Adjustment  + 25%  

(9.5 - 12.0) * (- 10)                        
      (-2.5)   * (- 10)                                     
        = 25% 

(submitted by Omar R. "DSMmaniac_Big_O") 

Notes

  • With this method my fuel trims are both with-in 1% of zero and my A/F Ratio are WBO2 shadow each other with-in 1-2% for an entire pull.
  • LTFT-Lo tends to be slightly unstable, so do not go crazy trying to get it perfect. With-in 3% of each other and with-in 5% of zero is acceptable.
  • Some changes to the Airflow Table at the 150 Hz point maybe needed when “cruise tuning.”
  • Adjustment to any slider in the airflow table WILL affect the two sliders adjacent to it.
  • For me, getting the 400 Hz point perfect created a nasty dip at the untunable 500-600 Hz range. Tuning the 500 Hz point using the 400 Hz point in the Airflow Table worked much better.
  • Sometimes tuning using a HZ point 100 more than what you are tuning, works better. So, instead of 1200 Hz sometimes using 1300 Hz works better.
  • This is not the “Ideal, Perfect” way to tune a MAFT, but it was sure easy. As with any tuning the main problem arises with boost leaks and fuel delivery discrepancies. So long as you have no boost leaks and your fuel system is working properly, this is an extremely easy and viable way to tune a MAFT.
maftcalibrationbywbo2.txt · Last modified: 2010/05/13 10:45 by dmertz