I am not sure what's going on with my evo x, the car is sputtering when I give it gas and then leans out. I thought it was my fuel pump so i changed it but it didn't fix the problem, i also swapped my relay with a different one and still did not solve it. The fuel pressure regulator hose is zip tied on so that's not it. I checked the spark plugs and they seem to be good, the maf was disabled to see if that could be the cause but it was still sputtering. I checked for vacuum leaks and could not find any but i doubt it would cause my car to lean out really bad and sputter. Im running out of ideas and things to check

My mods are ets intake, upper/lower IC piping, bigger intercooler, 1100cc fic injectors, 340lph aeromotive fuel pump, ams widemouth dp, cnt catback exhaust, grimspeed ebc, catch can, I am also running E85

I've attached a data log from evoscan when the car is at idle and another scan with me reving it a bit.
If you guys need anymore data logging I can be more than happy to send you more information.
Also the AFR's are listed under O2 sensor, I tapped into the rear O2 sensor to feed the afrs to the ecu (its 95% accurate to what I saw on my wideband gauge)


Your help would be greatly appreciated.

 

Did you ever solve this?? I have had this exact issue and my car has been at my mechanics for 6 months now!!! We are going crazy trying to figure it out.

 

Yea so it turns out it was my primary front oxygen sensor, or an exhaust leak or an issue with the tune lol I replaced all the gaskets on the exhaust, and the tuner disabled the front O2 sensor and the car was running fine again, he did some tweaks as well to compensate for the O2 sensor I suppose not sure but the car is running great again and I'm debating whether I should buy a new front primary O2 sensor or not lol good luck with your car hopefully you can figure out what it is, i was going crazy left and right trying to see what was wrong it.

 

Also check your fuel filter, it could be clogged or might need to be replaced, I did that in the process as well and I'm adding a fuel filter as well just to be safe.

 

If the front O2 sensor is failing it could cause a sputtering as you transition from cruise to acceleration as depending on the tune you are usually in closed loop using the o2 sensor feedback up until 100-120 load. To get around it you can have the car go open loop earlier on like 80 load and intentionally keep it slightly richer. Once you swap in a working O2 sensor you can then let it handle fueling until 100-120 load again for better MPG and drivability.