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MAF Tuning Lean after restart

Practical Reflash Tuning

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Totally stock 2012 Caprice 6.0l.

Playing around with logging and correcting the MAF error. It's in open loop eq commanded all set to 1 lambda not getting into PE at the moment.

After I stop to look at my first log make a few changes to the MAF table flash it back in and start back up and start logging it shows 10% lean across the board. If I drive around for awhile thing seems to get back to normal so i restart the log and seemingly am now getting good data or data I would have expected to see after starting up again.

Suggestions on what's happening upon starting up again?

its normal although it should be rich because of startup enrichment and slowly getting to lambda 1, usually it takes like 30sec and then you can start datalogging once the afr, if you decide to tune with closed loop make sure you use the special function to rest the trims

I think based on some research it's hot soaking something and once i drive around for awhile everything goes back to normal. Is there a fuel pid i can monitor to confirm that?

It is well known thing - indeed it is heat soaking.

any one have any info on what sensor is causing it to not use enough fuel when that happens out of curiosity?

Usually it's the intake air temp. Hotter air is less dense and thus needs less fuel for the same Air-Fuel Ratio.