My Evo drives fine but after driving for a while and the outside temp get warm, it suddenly goes to a lean a/f ratio...........idling and when driving at cruzing speed.

I can't understand what going on. Any help would be very helpful. TIA

 

Sounds like the AirTemp/Fuel correction calibration is incorrect. This table adds or pulls fuel according to the air temperature measures at your AIT sensor. I am just taking a guess here though, you would neeed to post your cal file for us to be able to tell completely.

 

What AFR do you consider as lean when cruising? Also may want to consider you WB02 sensor being mis-calibrated.

 

Thanks I'll pm you my calibration.

My AEM wideband is calibrated properly, I've compared it with an external wideband when I was dyno tuned. A/F ratio are leaned out of range and causing the car to miss fire and buck at times.

 

+1 Sounds like what's going on...


either that or your starting fuel tables are adding fuel for way too long...

What's the engine temp when this occurs? Approx how long after startup?

 

Also, sounds like the closed loop fuel control is not setup or needs to be tweaked too. This is if you have the wideband being fed to the AEM EMS and both the gauge and reading in the EMS are setup to read exactly the same.

Either way though the air temp fuel trim will need to be corrected as that is what seems to be the issue due to being heat soaked like mentioned above by GTVEVO.