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  #1  
Old 18-05-11
jwwells's Avatar
jwwells jwwells is offline
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Default code P0455 "Gross Evap Leak" and the Purge Valve

Hey All
I am working on a 99 9-3 Vert that has the P0455 "Gross Evap Leak" code and has been on for quite some time. The gas cap is sealed and all looks good without dropping the gas tank and looking around there. I've been doing quite a bit of research and want some opinions as to the legitimacy of my proposed repair.

Here's a brief description of the EVAP system.
When liquid gas is being filled into the fuel tank and sloshing around there is quite a bit of vapor hydrocarbons which need to be taken care of (not released into the atmosphere). The way they deal with it is vent the vapor first into a canister with carbon pellets in it which absorbs these free hydrocarbons. Then while you are running the engine the vacuum from the engine is used to draw the hydrocarbons out of the charcoal canister and into the combustion chamber to be burned.
Now the purge valve. The purge valve is a simple solenoid which is electromechanical which means when it is supplied power it opens to allow the vacuum to draw the hydrocarbons, but when the engine is off and no power is being supplied it is closed. The P0455 code is thrown when the pressure in the tank is too high and there isn't a vacuum present. This would indicate to the computer that perhaps the gas cap is off or some other leak. This could also be the case if the vacuum from the engine were being blocked entirely.

Here's what I did.

I pulled this purge valve and tried to clean it then after I plugged it back in and tried blowing through it with the engine running (it should be open when the ignition is ON) it was completely blocked no air moving through. So I bypassed this purge valve and used a one way valve from a parts car brake booster vacuum line. It now draws a healthy vacuum and although I haven't driven it for awhile hopefully it will now register the proper pressure (low) in the tank.

Will this work?

Is my understanding and overview of the system correct? Most of this info is from my reading on WIS.

Thanks, sorry for the long post.
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2001 9⁵ Black Auto Aero Wagon

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  #2  
Old 18-05-11
Frank_Drebin's Avatar
Frank_Drebin Frank_Drebin is offline
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Originally Posted by jwwells View Post
Hey All
I am working on a 99 9-3 Vert that has the P0455 "Gross Evap Leak" code and has been on for quite some time. The gas cap is sealed and all looks good without dropping the gas tank and looking around there. I've been doing quite a bit of research and want some opinions as to the legitimacy of my proposed repair.

Here's a brief description of the EVAP system.
When liquid gas is being filled into the fuel tank and sloshing around there is quite a bit of vapor hydrocarbons which need to be taken care of (not released into the atmosphere). The way they deal with it is vent the vapor first into a canister with carbon pellets in it which absorbs these free hydrocarbons. Then while you are running the engine the vacuum from the engine is used to draw the hydrocarbons out of the charcoal canister and into the combustion chamber to be burned.
Now the purge valve. The purge valve is a simple solenoid which is electromechanical which means when it is supplied power it opens to allow the vacuum to draw the hydrocarbons, but when the engine is off and no power is being supplied it is closed. The P0455 code is thrown when the pressure in the tank is too high and there isn't a vacuum present. This would indicate to the computer that perhaps the gas cap is off or some other leak. This could also be the case if the vacuum from the engine were being blocked entirely.

Here's what I did.

I pulled this purge valve and tried to clean it then after I plugged it back in and tried blowing through it with the engine running (it should be open when the ignition is ON) it was completely blocked no air moving through. So I bypassed this purge valve and used a one way valve from a parts car brake booster vacuum line. It now draws a healthy vacuum and although I haven't driven it for awhile hopefully it will now register the proper pressure (low) in the tank.

Will this work?

Is my understanding and overview of the system correct? Most of this info is from my reading on WIS.

Thanks, sorry for the long post.
You would do better to disconnect it and seal the line from the TB. Let the Evap valve vent to atmosphere. Having a constant pull will surely cause fuel flow issues at lower fuel levels.
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  #3  
Old 18-05-11
jwwells's Avatar
jwwells jwwells is offline
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Originally Posted by Frank_Drebin View Post
You would do better to disconnect it and seal the line from the TB. Let the Evap valve vent to atmosphere. Having a constant pull will surely cause fuel flow issues at lower fuel levels.
Well that would put me in the same position I am in now throwing the CEL and it won't pass inspection. Just curious... how would a vacuum in the tank cause fuel flow issues?
Thanks for the input!
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  #4  
Old 18-05-11
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watkins watkins is offline
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The purge valve is not open all the time when the engine is running. Only under certain situations. It also cycles rather than staying open or closed. The blow test doesnt mean much
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