ok, so... I've been bouncing around various sticky's and searched high and low without finding what I need to know. And quite honestly... there's a 94 z28 at a local dealer, this v6 might just get traded in. but anyway...

Where is the fuel pressure sensor?
and does anyone have a better, more easily read diagram of the charcoal cannister and the fuel pump sending unit?
also, is the engine supposed to stall when I pull the vacuum off the throttle body?

I'm trying to figure this all out... the code says "evap system leak". which I've had "fixed" 3 times now and it's been something new each time...

 

check shbox http://www.shbox.com/
http://www.shbox.com/1/evap_system.jpg

 

OK, how about your gas cap? Did you replace it? Is there rust around your filler neck? If so use sandpaper and remove the ruse so the cap makes a tight seal.

Do you smell gas around the gas cap (after filling) If so, you could have a pinhole in the filler neck.

The evap system issue will not cause drivability issues. However it's a pain in the butt to diagnose and fix.

 

ok ill bite on this, define drivability issues.

 

Please enlighten me. I've spoken to many GM techs, experts, and engineers about this. If you have a good seal in the gas tank and no small leaks in the filler neck or tank then that leaves the cannister, fuel pressure solenoid and purge valve. If the fuel system has the right pressure but the cannister, purge valve or solenoid is defective, then how does it cause driveability issues.

I'm asking because I'd like to know if I've been lied to by techs and mechanics.

 

ok if the canister is full of fuel and the system kicks in what happens? on mine the purge valve and solenoid both failed somehow causing the system to over pressure after the motor was shut off. if started soon after shutdown the system ran rich. with both failing the vacuum was open all the time while running and gas fumes into the vacuum system again added to the rich condition. this confused my fuel system causing it to lean up which effected all the cylinders, but not all cylinders were running rich, the cylinders close to the vacuum outlet on the intake got the fuel the ones farther away ran lean. so i was getting a lean and a rich code. this is my take on it and once the evap was corrected the lean rich condition went away so this is how i figured it happened. my canister was not full of fuel but i can just imagine what would happen if it was.

 

OK, fair enough. I had the same issue on my Aurora. Purge valve was stuck open and the gas fumes were filling up my cannister. I did end up changing the cannister, valve, and solenoid. I had no other engine codes besides the evap system, no difference in performance or gas mileage however. Maybe I was lucky that it wasn't bad enough to cause issues.

 

Stupid point - but on my '96, I got the evap codes too. Noted that the lines running to/from the canister behind the left rear wheel were all oxidized, hard and cracked. Swapped them out and haven't had a code since.