Very Strange Cobalt LSJ Issue. PLEASE HELP!

Hey everyone. I have an extremely strange issue with my car and I've tuned to this forum because I'm at a complete loss as to what's going on so I really hope someone can help. A quick background of the car, it's an 06 Cobalt SS that I turbo swapped. I ran the car all last summer turbo swapped without issue. A couple weeks before I put it away the car started acting very strange. As I cruise down the highway the car will randomly start running pig rich and the check engine light then flashes constantly with misfire. Logging the car, it's fine till it gets to operating temp then starts to do this. It shows open loop fault and starts commanding 10.1 AFR. Things i've tried are:

- Changed MAF sensor
- Changed MAP sensor
- Changed 02 sensor (rear is deleted)
- Changed ECU
- Tried a few older tunes thinkning a file may have gone corrupt while making changes
- Reinstalled my rear 02 sensor and put all DTC's back to stock. ZZperformance who deals with Cobalts said the car will do this when it can't complete a Catalyst Test. HPT shows the test being completed.

I've found 2 others with the same problem with a basiclly stock SS/SC Cobalt in the same boat as me so I don't believe it has anything to do with my turbo swap. But i'm completely stumped. I don't know why the car is showing an open loop fault and then commanding pig rich. Hopefully someone here can help or has had the same issue. I will attach a log to see. At the 5 min mark is when the car starts acting strange.

Thanks

rear O2 sensor in the stream?

Just the guy I'd like to reply haha. If anyone that may be able to help, it's you. Last year I ran no rear 02 with the catalyst test disabled and no issues till the end of summer. It did this problem a couple times and shutting the car off and starting it again would cure it. Then it just started doing it all the time one day.

Matt at zzp looked at my log this spring and said he's seen this before on a few cars that when the car can't complete a catalyst test it will do this open loop fault and command 10.1 afr. So I put the rear 02 back in and put all dtcs back to stock. Well it still wouldn't complete the test that's listed on the scanner. I found out over time the tune must have been corrupt because I tried a really old tune and it completed the test on the scanner with the catalyst test disabled.

It took about 3 times as long but would eventually do the same issue again. So I turned the catalyst test back on with the rear 02 in and last night drove it for about a half hour. The car was mint. Never acted up once. I then go to work this morning and it started acting up as soon as it hit operating temp. Then quit about 5 min later. It's like the car is struggling to complete a catalyst test randomly for some reason out of nowhere.

are the codes on but MIL off? SES enable? I ran into this issue with my 07 all the time, but HPT never bothered to add the rear 02 test tab in the file. so we are left with this. I never once had the issue on e85 with 1k injectors. only on pump gas was the issue ever showing up.

No kidding!? Please tell me you found a fix for it.... haha. But something tells me you just ran E85 and never looked back. I currently have them set up MIL on second error and SES enabled. Sadly I live in Canada so E isn't accessible to try. I was debating getting drums of E and cutting it with pump gas. But if that would even be the same cure you had would be up in the air. Is it worth emailing HPT? This is driving me nuts. So strange why it started out of nowhere.

a number of us tried in the past to do that, but nothing ever came of it. "it's not in the coding" it IS in the coding, or else it wouldn't do it. just like airlfow tables, and torque management on the 07 trans. it is in there, but it's a dead ecu so there is no point. put a motec on it and go about life.

There has to be a fix for this other than a $2500 ECU... I've only been able to find a handful of Balts that have actually had this problem. I'm sure you've seen more. But look how many modify their cobalts and don't run rear 02's at all without issues. I ran mine all last summer without one. And now putting it back in it still won't cure it. There must be something causing this. It's just so baffling. Ugh...

newer version of hpt?

Figured I would finish this thread off in case anyone ever has this problem. I'm sure you're a little curious too area.

I was pulling at straws talking to everyone I could and sent Alan (armcclure) on CSS a PM about this. He told me to send him my tune to try something which I did. Sure enough the car works perfectly fine now!

I asked him what he did. Turned the misfire sensitivity down! I'm running zzp s2 turbo cams in my set up and what's happening is the car is slightly misfiring at cruise speeds due to the cams. What happenes is the car thinks something is wrong and pours fuel into it like a limp mode. Here I thought the opposite. It was going rich then would start to misfire but it's the other way around.

So now it kinda makes sense Brian why your car wouldn't do it on E85 but would on pump gas. Better fuel quality probably helped with the misfire. If I remember correctly you were on GMR cams also correct? But anyways, lowering the misfire sensitivity fixed my issue. I'm so glad Alan had seen this before.

it did it regardless of cams. The final rendition of the car was on blue printed GMPP cams. still did it.