I have an 09 Cobalt SS/TC

A bought it about 3-4 months ago from a family friend. Car is very clean and well taken care of.
The car has a CAI, Downpipe, Stage 1 sensors, muffler cut off, and a nice computer tune. It's had all of this for awhile. 2 days after I got the car the IC broke and had to get a factory replacement.

Other than that all i've done is replace the spark plugs with new GM ones. Gapped at .33 about a month ago.

About 2 weeks ago I drove the car to work without any problems. Never got on it or anything like that. On the way home I noticed on the highway that it felt like it was cutting out a little just driving normal down the road. It wasnt until I was almost home that I checked the A/F gauge on the LCD and it's maxed out (18). I hooked my phone up to it when I got home with the App 'Torque' and I believe it was showing 26. I dont believe the check engine light had come on but with a scanner, it showed about 15 codes saying misfire's and 'lean on bank 1'

My brother is a GM mechanic and hes checked a few things out for me but there hasn't been anything obvious (i'll have to double check with him what all he checked).

So the car seems to idle OK when its cold/warming up, but the A/F gauge sticks to 14.7. When it gets warmed up, it'll immediately max out the gauge when you start it.

Any ideas?

Cold:
Cobalt cold - YouTube


warmed up:
Cobalt warmed up - YouTube

 

A/F is fine in open loop but super lean in closed loop is a dead sign of a bad primary o2 sensor (b1s1 o2).

Can you get the exact codes btw?

 

I'll have to get the codes again.

hmm... we hooked a Tech II up and it showed the sensor was working fine

 

Stop driving your gonna pop your motor dood. Get that fixed and drive something else. That's dangerous. Way above bad lol

 

What phone do you have?

 

Galaxy S3...


I have 8 other cars to drive.. this is just sitting here in the garage collecting dust.

 

Tuned? Seems like a bad o2 making you lean as ****

 

I can tell you with almost 100% certainty that your b1s1 o2 is bad.

Again, when your a/f is good in open loop but goes to crap in closed loop is a clear sign of a failed/failing primary o2.

 

I believe the codes were P2177 and P2187. The O2 sensor was reading like .991 lambda

 

I need a little more info. Is that with the engine cold or hot? I'll assume for the moment that's with a hot engine in closed loop considering the o2 is basically useless in open loop.

You're throwing b1s1 lean codes, yet the o2 is reading rich (.991lambda is about 14.5a/f) then reason should tell your tech friend there that your o2 is having issues. Have him check your rail pressure, maf frequency, maps and injector pulse widths in CLOSED LOOP if you would like to waste your time further troubleshooting, but I'm still sticking with a bad primary o2.

I hope he even knows the difference between open and closed loop for your sake..