15 February 2011

Hondata S300 and IAT compensation

More to share on tuning using S300.  

Background: I was tuning my car for part throttle (cruising) and managed to have a stable 14.7 AFR reading through column 1 to 5.  However after I shut down the engine for a while (couple of hours) and drove again,  I got lean readings (greater than 14.7).  I was expecting richer AFR than 14.7 rather leaner reading as the engine has cooled down.

I did a datalog and realised that the IAT readings were quite high which caused the ECU to reduce the duty cycle, resulting in a leaner AFR reading.  This might be the IAT sensor being heated up by the hot intake manifold.

2 lessons learnt:

1) When tuning your engine, try to make sure the IAT and ECT values are the same for each run as it affects the AFR value greatly.

2)   If possible, try to find a way to insulate the IAT sensor or minimise heat transfer from the Intake Manifold to get a more accurate reading.

Once u manage to tune your engine as desired (with constant ECT and IAT values),  you can adjust the fuel compensation for IAT and ECT accordingly since the default value may not be the ideal compensation required.


  1. Hi, could you post the before and after settings of your ECT & IAT compensation? Would like to know the approx. difference of the before or after. :)


  2. In my case, I simply set the previous negative values to 0.

    Eg. Under 70° and 100° it was -0.5 and -1.3 respectively. I set it to 0 and 0.

  3. Have you adjusted any of the positive fuel low temp settings. Or any of the hi load corrections?

  4. I didnt bother to adjust any of the temp below 51 degree C, since the lowest ambient temp never drops below 28.

    As for the high load correction, i set it to 0% compensation for temperature above 51 degree C as well.

  5. Have you adjusted any of the settings for gear compensation?
    I have the same setup as you with the PLX wideband.
    I just installed a GM IET in the air intake by the throttle body. I read that this sensor is about 10 degrees of from the factory sensor. My car use to read 148 when I parked it in 70 degree weather. Now treat about 80 degrees.

  6. I did not adjust any of the settings for the gear compensation. Cause I have gone into that far of tuning yet, and didn't have the need to do so.

    As for the GM IET, I have no experience with it at all. However, u can adjust the compensation accordingly by change the temperature in the table if u are sure it is 10 degree off. eg. instead of 51C change it to 61C.