so heres the story. just last friday i go out to start my car before work to warm it. it wont start. the engine cranks, but it just wasnt igniting or something. anyways, so it goes, on the way to the dealership. now i guess the theft deterent code went off (we have 2 cobalts at this house, someone must have put the wrong key in mine) so that took care of that. but for some reason the fuel trim is at 17. now i dont know anything about that, except for that means its running rich, and my dad said it needed to be in the 0 to -2 range. anyways, the dealer says this is because of my k&n intake and suggested that i reinstall the stock one and have them run more tests.

if anyone can help in diagnosing this problem it would be much appreciated.

 

so...the dealership ran tests, and said ur afr(air to fuel ratio) was 17? n ur dad says u wanna be in the 0, -2?!? i'm confused. i thought the lower the richer? am i wrong? i thought 12-14 was ideal?

 

Yeah, I am alittle confused as well. Which fuel trim do they say is at 17 and is wrong? are they talking about the STFT or LTFT? I am not sure what is normal, but there is always going to be some kind of value in the fuel trim.

Also AFR stoich for pump gas without ethanol is 14.7, 14.1 for gas with 10% ethanol.

AFR in PE you usually want to see around 11 give or take.

 

i'm sure they were talking about stft or ltft. 17 is out of specs....ideally, it should stay between +/-5%. it will always bounce aound, since the ecm is always adjusting the fuel to reach a perfect afr

 

OK here we go, first you car is running lean. The K&N filter is allowing more air into the engine than the stock air filter. Because of this the computer is attempting to compensate for the extra air by adding extra fuel. In the pcm there are preprogramed tables for fuel injection. When the dealership said yours was at 17 thats what they where refering too, the fuel injection tables. When the fuel tables go positive the computer is adding fuel because its detecting a lean condition. When the tables go negitive the pcm is taking fuel away because its detecting a rich condition. The pcm will attempt to keep the A/F ratio around 14.7 to 1 but it can only do so much. Now if you have had the K&N filter on it for a long time I wouldnt worry about it.

 

ive had the SRI since april i believe, and it was the ltft that was at 17, but i understand what youre saying about how it owuld adjust for that. it might possibly be from the cold weather as well, since the air is more dense, but i could be wrong.