Engine weird a/f ratio, need help.

Wilson2608

So ill try to help you out as much as i can. The reason you engine idles near 14.7 at first start up is because your car is in open loop( from my understanding) which means it isn't relying on the sensors to calculate the amount of fuel injected into the cylinder. Once warmed up, the vehicle is now in closed loop. This means the vehicles is relying on the sensors, and this is where LTFT (long term fuel trim) and STFT (Short term fuel trim) come into place. Your STFT takes immediate calculations of the AFR, but has no memory that it can store it into therefore it can only change real time AFR. So if I have a rich fuel problem, it will compensate. LTFT has a memory based on the results of STFT and can affect your AFR at all times during closed loop. The LTFT "remembers" the issues of the STFT and will always adjust for it. Anyways, what i'm trying to say is that if you have a intake leak, maf problems, etc your LTFT will compensate for it. Im not the best at explaining things, especially things like this lol so ill try to provide a brief summary of what i just said. The reason( i think) your car hits 13.5 afr after entering closed is because your Long Term Fuel Trim is telling the car "hey man theres a unknown air entering the engine somewhere, and i need to add more gas to compensate for this lean condition (intake leak)". Thus causing a rich condition. As for why the car goes to 15ish under load im not to sure. A vacuum leak becomes less of a issue under load. I hope i've helped, i can't tell you the exact problem but it's possible your tuner doesnt know what hes doing as well. (if the car is tuned) Do you have a aftermarket intake manifold? if both sensors are messed up it obviously has to be a problem with the air/ or gas entering BOTH sides of the car. SO the leak (if any leak) would have to be near the intake mani, not the intake piping itself.
Hope I could help you find the problem.

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Stillen G3, z1 Intake Manifold, Stillen Headers, Z1 HFC's, Stillen Catback. 330whp 267 ft- lbs tuned at Z1 motorsports.