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What is the Evap system exactly

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Old Apr 22, 2012, 04:11 PM
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What is the Evap system exactly

This may be the wrong place to post this but whatever. I have an 05 VIII and the check engine light is on for the evap system. I'm not really sure what that is and if it is worth getting fixed? Any help would be appreciated
Old Apr 22, 2012, 06:46 PM
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I'm just gonna say this, do a Google search.
But in short, the Evap system takes fuel vapors and burns them in the engine instead of venting them into the atmosphere.
Old Apr 22, 2012, 06:47 PM
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The EVAP system collects the fuel vapors in the fuel tank and releases them to the intake manifold to be burned while cruising. It's a fuel mileage/emissions system. The entire system is located under the rear driver's side of the car by the filler neck. It's not necessary but it's not like there's a ton of weight advantage in deleting it.

You'll notice a slight mileage drop if you delete it, you'll also need to have your ROM edited to remove the check for the system or you'll have a perpetual CEL.

Which code is it? Could be something as dumb as you not getting the gas cap all the way on one day.
Old Apr 22, 2012, 08:45 PM
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Originally Posted by cmspaz

Which code is it? Could be something as dumb as you not getting the gas cap all the way on one day.
This. Gas cap is part of the evap emissions system and would be the first thing I'd check. Could be worn or not on at all. Good luck.
Old Apr 22, 2012, 11:05 PM
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The two codes are
P0401
P0456
The guy I bought the car from told me that the evap valve was missing and it would be like 300 bucks to fix at the dealership he checked. As for the other code I think it is some exhaust leak or something
Old Apr 23, 2012, 11:37 AM
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Originally Posted by gturner26
The two codes are
P0401
P0456
The guy I bought the car from told me that the evap valve was missing and it would be like 300 bucks to fix at the dealership he checked. As for the other code I think it is some exhaust leak or something
P0401 is an insuffiecient EGR flow code. What it usually means is that the passages are clogged inside the intake manifold.

To fix:

Remove the egr valve on the lower right side of the intake (under the throttle body) Use a coat-hanger and perform an abortion (scraping, poking, clearing the passages that go to the egr valve, use brake cleaner too, helps break up all that **** in there. I have to do mine every 15-20k miles, if the code comes back immediately, you either didn't do it well enough, or the valve is clogged/damaged too. Check the condition of the ports on the egr valve itself while its out. Clean if necessary, clear codes, and go for a drive.

Keeps us posted.
Old Apr 23, 2012, 01:32 PM
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or you can just remove the egr entirely.
Old Apr 23, 2012, 04:18 PM
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There are a bunch of excellent EGR valve cleaning (P0401) videos on youtube. It isn't necessary to watch one for your specific vehicle to get the gist of what you need to do.

I might suggest using a shop vac in conjunction with that coat hanger abortion.
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