LTFT's Change After Pumping Gas
 

I've noticed that after I get gas, my LTFT's change. For example, the other day I stopped to get gas and prior to stopping my LTFT's were 0 to -2. After getting gas, they were -12. After I drove around for a few miles, they went back to 0 to -2. Why does this happen?

BTW - I'm checking them with my dash mounted Scanmaster.

One time I left my vehicle running (and logging) while filling up with gas. During the 5 minutes or so I was filling, my fuel trims went from -2 to -10. Then they gradually returned to normal over the next few minutes.
I suspect the following explanation:
The fuel filler lid was removed, affecting the evaporative purge system. The amount of gas vapors in the fuel tank increases when you fill up from all the splashing. The evap purge sucks up these vapors creating an artificially rich condition due to umetered fuel entering the intake. After the fuel lid is replaced - the evap purge will slowly suck all of the vapors out of the fuel tank, and the rich condition will go away.
Sound reasonable?

Seems to be normal, mine does the same thing, had me worried for a little but after a few minutes it returns to normal.

It could also be the heat of your exhaust w/ the LT's. Your O2 sensors (the suckers that are responsible for LTerms) are very heat dependant. It may take a couple minutes after shutting the car down to get everything back up to temperature with a free flowing exhaust.

I like the evap system idea as well.

This sounds reasonable. :nod:
Thanks for the replies !