On the subject of Winter Gas
 

Having seen snippets referring to crappy Winter Gas, I think I may have just put in the first tank full.

I'm seeing AFR warnings more often, and also more knock sensing, even though I have not done much to the tune lately.

Research that I have done indicates that the main performance difference between summer and winter formulations is the stoichiometric AFR, but that the octane rating is maintained.

If that is true, then it would seem to me that the best fix is to simply change the REQ_FUEL value by the proper percentage. The effect will be to decrease the AFR to the appropriate level everywhere in the tune, that is, for all open loop processes. The closed loop items will not be affected because they are really based on Lambda, though reported as AFR.

When summer gas comes back, just revert to your original REQ_FUEL setting.

Thoughts?

I feel a little like I'm talking to myself here, but, for the record, my issue was more that the cold AIT needed more MAT correction. I went to 104% @ 50*F and now AFR's are right.

Good to know. I would have had no clue.

When is the last time your O2 sensor was calibrated, if possible? Mine is usually a bit off from drastic season changes for which I also re-tune. Though I bet some of this correction would help me out too.

Re-calibrated within 3k miles, 4 months.

Where are you that they are offering winter gas?? We don't even have it at our pumps yet.

See my second post. My issue was not due to winter gas, but the idea I posed can still be considered.

I'm in SC. winter gas in SC

I've had issues with "winter grade fuel" as well. It could be a combination of both colder air and worse gas.

My AFRs are being mantained. I've found that i'm unable to run as much timing as i normally would.

Sounds like octane, not Stoichiometry
 

Which, if open loop, would more indicate lower octane than lower stoichiometric AFR. Hence the reason for this thread, to find out if the information I found was valid. Thanks for another data point.