Full Tank Only = Gas Smell, Racing Idle and Stall

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Nov 26, 2002
Texas & BWI Area
1998 Chevrolet Camaro, 3800 Series II History, In tank pump replaced 24,000k ago...and it is noisy on idle and annoying. Factory unit was whisper silent. Only when I fill the tank, I will smell gasoline in the car and outside of it. A few miles later the idle was start racing and stall out. The stall especially happens if take the car through curve. Often the stall will occur while idling at a stop light. The car will restart easily, but I am fear stalls in precarious or in catastrophic places like in middle of the road. The only historical code I remember is that the car has thrown some kind of EVAP code for the past few years. Before I go changing out the IAC Motor/Valve, EVAP Canister & Solenoid, etc, any guidance what this could be? Online sources say the Solenoid Valve, EVAP hoses, and MAP sensor are culprits. Why do curves induce stalls more in this situation? Why does this only happen on full tanks? Thanks
Full tanks, and stalling while in a curve/turn could make sense if the pump wasn't being completely submerged.....i.e.: not slurping up the fuel properly.....BUT if the tank is full, I can't understand that. How "full" are we talking? When you fill up, do you typically fill up to the "first click"....? Or do you round up to the next cent/dollar amount...? Or do you fill it "completely" i.e.: to the top of the filler neck? In the latter cases, I've heard of the "charcoal" or "EVAP" canister getting soaked in alcohol....which then makes the "charcoal" useless, since it's soaked in fuel, it can no longer properly filter the "air".....and that could cause the smell. Other than that...how's your MPG? Any signs of "running rich" or anything? When my vehicle had a bunch of broken/dry rotted vacuum lines, my MPG took a BIG hit.....I was lucky to get 150 miles on a tank....now I'm averaging 250-300 miles on a tank..... BUT, I'd think you'd have a CEL if it was anything charcoal canister related....?
Yes MPG has been down for years and I have tried everything from premium plugs, wires, O2 sensors, synthetic oils and everything to counteract. I did plus 0+ fitment change from P235/55/16 to p245/50/16 tires. But I cannot see that as devastating my odometer so much. Yes, it occurs at top off, but (no that it justifies that now) but have been for 14 years almost without problems in the car. On running rich, I have suspected this for years but how do we diagnose that? If this is clue, on some of the erratic idles of the past the fuel smell have been worst, as if it could have been venting out? Thank you guys so much!
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It's what's sometimes called a purge valve. Normally controls activate it only at certain speeds, yours is stuck open. It should throw a code you can read off the PCM.
Ditto, purge valve could be part of the problem. What happens is you get a "rich stall", and it usually doesn't set a fuel mixture related code because it happens so fast. There should be some sort of liquid/vapor separator on/near the tank. In an ideal world, this should keep any liquid gasoline out of the evap system, but they degrade, especially with constant overfilling. Once you get liquid gasoline in the evap system, it causes havoc with whatever component it contacts. See if GM released any updated EVAP components or PCM related upgrades/reprograms for the concern.
This issue is a known problem in my car and is caused or at least aggravated by constantly over filling the tank. Our fleet trucks have also occasionally displayed these symptoms.
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