Could EVAP makes the car goes that rich ?

[wesam]

I have a problem recently in my C5
Some times when its parked for long time in hot weather it will go rich almost 2 to 3 complete points
Like 12 AFR in all places for short periods and come back to 14.7 after 2-4 Min
-fuel pressure steady
-comanded AFR is steady
-volatge is steady
-MAP is steady while idle before and after the problem
-problem happens in idle or while cruzing every where in the VE table by almost the same amount 15-20% extra fuel
-the car has two wide bands in each bank and they reads the same so its not bank to bank related or wide band issue
-The car is tuned SD open loop so I think there is some thing wrong with my EVAP system makes it go that rich
Any suggestions to trace the problem

[joecar]

That is possible.

Post a log file.

Try experiement: disable EVAP/PURGE, see same thing happens or not.

[ChipsByAl]

You may want to disconnect the pipe to the evap purge valve and cap the valve and pipe. If the evap system attempts to purge the canister and it is oversaturated with fuel, the purge valve will draw raw fuel from the canister. Topping off the fuel tank too much is a common cause for an excessively fueled canister. Don't leave the evap lines disabled like that though.
Al