Hello,
I have a 2010 Cobalt SS with the GM Stage 1 upgrade installed. I'm very happy with the performance. However, recently I've been getting the CEL coming on. I ran a diagnostic test with an engine analyzer (OBD-II Scan Tool) and the code is for the air/fuel ratio being too lean. When I set the RPD to read air/fuel ratio and drive around, the gauge indicates the air/fuel is far too lean (18.0) when I'm not pressing down very hard on the accelerator and I'm in gear. The air/fuel drops to 14.5-14.8 if I gently hit the gas or if I shift into neutral and no longer press the accelerator. I don't hear any change in engine revs or any other indication that the engine is not functioning properly. One last note is that every so often the CEL goes back off after I've been parked for a while for a while.
Has anyone else had this problem? Is it actually the air/fuel mixture is too lean or is this an electronic problem that causes the RPD to indicate too lean an air/fuel ratio that then triggers the CEL?
Any advice would be greatly appreciated. Thanks.

 

I always thought a cai caused the car to run rich.

 

Thanks, ATOMBomb.
I don't have a cold air intake on my Cobalt. Does cai stand for something else?

 

ok so on ur rpd, at idle is the a/f at 18 or is it at the 14.5ish u said it goes to when u press the accelerator? 14.5ish is what it should be at idle and at crusing speeds. if ur running 18a/f at idle then u could have a bad injector, or bad o2 sensor, I'm not sure if a bad cat would do that, but they can mess things up to. someone else chime in

 

How's the A/F ratio at full throttle? Sounds like you have an air leak somewhere or possibly a boost control issue. Would need more info to determine the actual cause but the lean code is because the car is seeing 18:1 AFR, it's possible the sensor is reading wrong but if it's returning to normal at idle it makes me think it's working ok, and you have some sort of other mechanical failure.

 

air or boost leak after turbo would make it rich not lean

 

No. At idle it will be lean, vacuum pulls more air in. At boost it will be rich.

 

Under boost, yes. Out of boost, not so much.