Help understanding some of the basics!

[jtrosky]

Attached below is a scanner log that I took of my 2012 Impala (3.6L LFX engine, 6T70 trans) during a recent trip to the local pizza shop. The log begins at a cold start of the car. I have some basic questions about a few specific things that I'm sure is basic stuff for most of you guys - it would be a huge help if you could help me understand why some of this occurs... Below is a list of frames and my question regarding the data starting at that frame. Like I said, any guidance would be greatly appreciated!

8090 - STFT's start pulling more and more fuel in closed loop (STFT's go down to -20'ish and stay there for a bit).
9543 - After sitting at -20'ish for a while, STFT's go back to "normal" values

20463 - While coasting, goes from closed loop to open loop and STFTs spike to +34.4
20626 - Back to closed loop and STFTs go back to "normal"

53550 - Commanded AFR goes down to 12.25 as I enter PE - while in PE, O2 sensors constantly read high (over 800mv) - does that mean I'm running too rich while in PE?

60031 - After a brief highway trip, I exit the highway and sit at idle for a bit while waiting to pull out into traffic from end of highway exit ramp. While idling, I go into Open loop and commanded AFR goes to 15.5 for a while... During this time, O2 values are constantly below 50mv. When I press the gas to pull out, I go back into closed loop and commanded AFR goes back to normal.

64930 - While coasting downhill, go in and out of open loop repeatedly and STFTs spike to +34.4 while in open loop.

I'm just trying to understand why the car does these things (and to make sure it's normal)...

The log is slightly too large to attach here (about 5mb), so I shared it via my Dropbox.

Log file: https://www.dropbox.com/s/hiy3nl3qti...Pizza.hpl?dl=0
Here is the scanner config file that I'm using (2.24): 2012Impala-Basic2.cfg

Like I said, any input would be greatly appreciated!

Thank you!

[CRTD]

One thing is for sure, When your in PE mode your O2's should stay high. If not, you are above 14.6:1 (gas) and that's a problem.

[jtrosky]

Thank you very much for the feedback. I guess I kind of forgot that the "narrow band" O2 sensors on most stock cars only try to maintain 14.25 AFR (at least on my DI car)so the O2 sensors will read "high" if the AFR is lower than that (or will read low if the AFR is higher than that).

At least that is the way I understnad it - someone please correct me if I'm wrong. I never thought that I would get this far into tuning and never expected to want/need a wide-band, but damn is it tough to know what's really going on without one!!

[Dr. Nopps]

8090-20626 First 4 events look like a "sanity" check to make sure cats are working/installed properly.
53550 Once you're in PE I believe your car only uses data from the last fuel trim cell referenced right before PE was entered, so it's crucial to iron out that area first. (Seems more coverage on that in LNF & 4cyl section) 60031 It's common (early Cavaliers in my personal experience) for a PCM to require at least 1% throttle to allow Closed Loop. 64930 And the last event sounds like the result of DFCO (or whatever it's called on your car) while cruising to save gas.

[jtrosky]

First - thanks for the response - I appreciate the input.

Regarding the last event and DFCO - I have DFCO disabled. I hated the way it caused my RPMs to jump around when it engaged and disengaged - especially when it went into and out of DFCO within seconds. Drove me crazy.

However, while I don't care about wasting fuel becuase I disabled DFCO, I don't want to be causing any other issues by disabling it. And that's part of the reason I'm asking some of these questions - I want to make sure disabling DFCO isn't causing any issues that I'm not aware of....