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Hi,

Discovered something interesting this weekend. Was running around logging fuel trims and doing some tweaking Saturday morning. Trims were good, but I was getting low on gas so I stopped and filled up.

Fired back up the trims went -12 across the board. A little perplexed at first, they slowly went back to -4 ~ 0 over the course of 15 minutes. It got me thinking that the cause was the temparature of the gasoline in the ground was lower that the ambient air (about 75ish). Since cold air is denser and thus tends to make an engine go leaner, it seems reasonable that gasoline would do the same thing, but only in reverse.

I don't exactly know what to do with this information, but I made mashed potato sculptures of the concept all during dinner last night...

John.
 

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John,

That is interesting, Ive never heard of anything like this before..... My guess would probably have something to do with possibly the fuel temp diffs as well..... I will stay tuned to see what you find out bro

Carl,
Im ba-a-a-a-ack! ;) :cool: D

TJ
 

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DELLZ06 said:
Hi,

Discovered something interesting this weekend. Was running around logging fuel trims and doing some tweaking Saturday morning. Trims were good, but I was getting low on gas so I stopped and filled up.

Fired back up the trims went -12 across the board. A little perplexed at first, they slowly went back to -4 ~ 0 over the course of 15 minutes. It got me thinking that the cause was the temparature of the gasoline in the ground was lower that the ambient air (about 75ish). Since cold air is denser and thus tends to make an engine go leaner, it seems reasonable that gasoline would do the same thing, but only in reverse.

I don't exactly know what to do with this information, but I made mashed potato sculptures of the concept all during dinner last night...

John.
Yep, I've seen this many times. Usually takes me a drive to work for fuel trims to settle back to normal. I don't know why it happens for sure, but I surmise it's from the evap system. You can test by using the VCM controls and activating the purge solenoid and watching the fuel trims.
 

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Does the Vette also measures the air pressure at start up? (Barometric pressure).
F-bodies do that and depending on the pressure they modify the engine settings. I saw that driving on the alps: the LTFT did change progressively as I went up: at the end they was out by 7% at least. Turned off the engine, then on and everything went back to normal.
I think also the engine temparature at start up plays a rule and it could explain what you noticed.
 

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My thinking on this is when you open the gas tank pressure is released and after resealing it takes a little time for the pressure to build back up again.
Try openning and closing the tank without adding fuel and see if I'm right.
 

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Blue Devil said:
John,

That is interesting, Ive never heard of anything like this before..... My guess would probably have something to do with possibly the fuel temp diffs as well..... I will stay tuned to see what you find out bro

Carl,
Im ba-a-a-a-ack! ;) :cool: D

TJ
Blue devil...I love your rims. What kind are they? They look like 3-piece.
 
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