LTFT's Change After Pumping Gas

[dropkick]

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.

[262 77]

Moved to tunning and performance forum.

[JandJsTA]

Originally posted by dropkick
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.

I would suspect it would have something to do with the cooling of the O2s while you were getting gas... next time you start your car from a cold start or after it has been sitting check your LTFTs before the car gets up to full operating temp and see if the results are the same :)

[DebianDog]

I thought is was the octane check that ran after every fill up?

[JandJsTA]

Originally posted by DebianDog
I thought is was the octane check that ran after every fill up?

It very well could be but would it pull fuel on an octane check?? sounds backwards no:confused:

[DebianDog]

No what happens is when you refuel (full) it picks a fuel map. So... if you got bad, cheap gas last time it would change. Right? :xfings:

[smiley]

Originally posted by DebianDog
I thought is was the octane check that ran after every fill up?

i thought it did something either when the fuel level got low or was refilled but i couldn't remember...... :thumbup:

[MYTURBOT/A]

When you fill your tank full you end up with gas over filling into your charcoal canister which inturn gets pulled through the evap system and into your intake to be burned and reduce fuel vapor released into the atmosphere. It`s a emissions thing.;)

[DebianDog]

Originally posted by MYTURBOT/A
When you fill your tank full you end up with gas over filling into your charcoal canister which inturn gets pulled through the evap system and into your intake to be burned and reduce fuel vapor released into the atmosphere. It`s a emissions thing.;)

That too ;) It also checks the octane level on a refill.

[BigKID]

Dont mean to pull up an old thread but this is very interesting to me.
How do you suppose the pcm 'checks' your octane level?? :think:

[jimmyblue]

Also the whole evap system gets air instead of gasoline
vapor in it, temporarily changing an unmetered fuel
source into an unmetered air source, and then it goes
back once the tank is purged of air by the evap system.