Pontiac Repair: Code p0455, vent valve, gross leak

Question
Hi Todd,
I am hoping you can help me with a GEO Tracker problem.  I realize your area of expertise is with GM's but you have been very helpful to me in the past so I thought I would check with you on this one.   I have a 97 GEO Tracker that has the service engine soon light on.  The code reader shows p0455 (Evaporative System malfunction, Gross Leak).  I have tried everything I know to fix it...From the gas cap, checking all the lines, replaces all of the EVAP components (used from junk yard),,including the Fuel Tank Pressure Sensor, EVAP VSV Valve, EGR VSV and Evap canister.  There are no visible leaks or smell of fumes.  Every time I reset the Code, I can drive between 6 and 7 miles and the Service Engine light goes back on.  One thing I noticed is that it doesn't seem to go on when the engine is accelerating, but it goes on when I slow down to make the turn 7 miles into the drive.  Today I replaced the fuel filter as well thinking that might be clogged.  The funny thing is... the car runs great..no hesitation and lots of power.  Other than the light being on, you wouldn't suspect any issues.  I need to get the car inspected but can't until the reason for the service light is fixed.

Do you have any thoughts on this?  Again, sorry to bother you with this, but there are currently no experts for the GEO Tracker.

Thanks for your help!
Rick

Answer
Hi rick:

well I woked for a SUZUKI dealer and that is what this is but I had limited exposure to them. that code is caused by the system wants to purge but for some reason it's not or the computer is not seeing the purge event take place. The most common problems are a gas cap. Or a gas cap filler pipe being rottted out especially if you live in the rust bet. Besides that you could have a bad vent valve or purge valve. the issue your going to have here is you have no control over when the system wants to purge If you had a true scan tool you coauld command on either the vent or purge valve and see if they inddde are working or it's a control problem from the computer or a wiring issue to the component. If you knew the purge valve was running you can pull off the vacuum line going to the tank and see if there is vacuum present there or not. I have seen the purge vakves stuck and not turn on. I have seen Carbon from the charcole canister get stick in the valves too. Soor I can't be of more help but those are the things to check. Good luck :)