Cobalt LNF STFT woes

[firehawk618]

Hello and thank you for looking at my thread.

I have been doing TONS of reading and experimenting with tuning on my recently acquired 2009 Cobalt SS.

I basically followed Backyardturbo_FTW and cobaltssoverbooster guides on how to dial in the MAF. ***THANK YOU TWO for all the great guides!***

My thought was to make my main focus getting my trims dialed in.

I thought I had it pretty good. 3 days of logging and I had things nailed down to ~-3 STFT so I thought.

Today I fire up my car and boom suddenly it's more around -18. I made ZERO changes to the tune. In fact I haven't flashed anything to my car since I was averaging around -3.

This has happened to me before with this car when trying to get things dialed in trim wise.

I have removed and inspected every element of my intake piping and did a check for vacuum / boost leaks.

I had a brand new MAF sitting here handy incase this happened again. I threw the new OEM one in and it made zero change.

Does anyone have any suggestions as to things I might check? My logic says if I had a post maf leak wouldn't I see positive trims since unmetered air was getting in?

I am wondering if my primary o2 sensor is failing?

If you guys have any input I would greatly appreciate it.

See the two logs + my current tune.

Thanks!

[mkriebs]

Yeah, I had this problem a while ago and I changed out the O2 sensor. The sensor actually wasn't bad, but I had found the previous owner had added an extension, so it wasn't getting the appropriate airflow. Might not be a bad idea to change out the O2 sensor. Also, what has the weather been doing near you? This is a tricky time of year where fuel trims can be a little tougher to dial in, since it can be cold one day and warm the next.

[firehawk618]

Yeah, I had this problem a while ago and I changed out the O2 sensor. The sensor actually wasn't bad, but I had found the previous owner had added an extension, so it wasn't getting the appropriate airflow. Might not be a bad idea to change out the O2 sensor. Also, what has the weather been doing near you? This is a tricky time of year where fuel trims can be a little tougher to dial in, since it can be cold one day and warm the next.

Sorry for my slow response. I assumed I would get an email notification for any responses here.

I think you're right. The weather has been ~40 degrees and dry with the good logs for days then when it went to crap it was a rainy PACNW day.

I have noticed that the humidity plays a huge factor with my car.

I have pretty much come to the conclusion that +- 3% just isn't going to happen here with my car.

I have settled for +- 10%.

When it's wet and rainy it hoovers near -10%. When it's dry it hoovers around +10%

I just don't know any way to get this range any tighter since this car doesn't have a humidity sensor.

The temps from dry to wet have been generally pretty close so I don't think temp can be the issue.


I did pick up a new oem O2 sensor since they're relatively cheap for our cars *thank goodness* but haven't installed it yet.

I watch the PCM's AFR readings on my RPD and my AEM at the same time. They're both pretty much the same so that to me kind of rules out a flakey o2 sensor but I will change it anyhow the next time I'm working in the area of the O2 sensor.

[T-Man]

OP,

Are you running the factory air box?

[firehawk618]

OP,

Are you running the factory air box?

No, it came with the HAHN intake.

To be honest I have been trying to find real information *besides HAHN website* regarding just how much of a restriction the factory one is. I would get a factory one and put it in if I didn't take a HP hit. I know a lot of cars the factory one isn't even a restriction yet people replace them anyways.

[PSYKOSTEVO]

You can crank a piss load of power through that stock airbox. But then you don't hear the turbo as much. People with LNFs sink a lot of money into intakes and cat back......noise is power to some people.

[2000Firehawk]

You can crank a piss load of power through that stock airbox. But then you don't hear the turbo as much. People with LNFs sink a lot of money into intakes and cat back......noise is power to some people.

So true...
Same thing with DPs, every one wants a catless DP
My testing shows that the stock DP with the 2nd cat 'cored', a simple fix, without even removing the DP, works just as well as an aftermarket catless DP.
My last time at the track with my HHR SS automatic, I ran a 12.28 @ 112.67 with the stock DP with a 'cored' 2nd cat.
Still running with the stock airbox, with a K&N airtube/filter.

[T-Man]

No, it came with the HAHN intake.

To be honest I have been trying to find real information *besides HAHN website* regarding just how much of a restriction the factory one is. I would get a factory one and put it in if I didn't take a HP hit. I know a lot of cars the factory one isn't even a restriction yet people replace them anyways.

I'd suggest getting rid of the Hahn and moving back to a modified air box (modified snorkel, drop in or quality paper) and a ZZP intake tube. Your fueling will be much easier to get it where you want and maintain. I also believe you'll make as much if not more power. Only downside is you lose the additional turbo/bpv noise.

Good luck man.

[mkriebs]

I ran a Precision 5557 through the stock airbox on my balt when I had it. The ONLY restriction in the stock box is that corrugated elbow, which I believe it was ZZP who sells a silicone replacement.

It's likely the humidity plays a bit of a role, but the Hahn intake plays more of a role in the STFT swing. But, your tune may just need some more work.