EVAP leak?

MR.MAGUILACUTTY

MEMBER
2007 CHEVROLET AVALANCHE
V8
AUTOMATIC
215,000 MILES

I had a check engine code pop up that was an evap leak. I replaced the vapor canister last week then today I changed the charcoal canister. After changing the canister, I drove 50 miles to see if the light would come back on and it didn’t nor did anything seem out of the ordinary. I stopped to get gas and when I opened the cap a lot of air came out then the pump kept stopping and I had to keep doing it in order for the gas to keep pumping. Not sure what’s wrong. Any assistance or advice would be appreciated. Thank you

3 Replies

BRENDON S

MECHANIC
653 POSTS

Good morning, MR.MAGUILACUTTY,

What exactly was the code? Also was it a small leak or a large leak that was detected?

The Vapor canister is the charcoal canister. Fuel vapors make their way into the vapor canister and are stored in charcoal.

The reason you can't fill it with fuel is because the vapors can't go anywhere and set off the pressure sensor in the pump handle. As you fill the tank the air inside is being replaced with fuel. If the air can't go anywhere, the only place left is for it to go up the filler tube. Which will activate the pressure sensor in the pump handle.

Can you send me a picture of the items you replaced?

A large leak could be a fuel cap. To get one go to the dealer, do not buy one from the parts store, it will not fix the issue as they are usually built incorrectly and not made for your particular system. Another possibility is the Vent Valve.

When diagnosing a leak condition, a smoke machine is used. The smoke machine fills the system with smoke and helps you to identify the leak.

There was an update to the vent valve that GM did. The problem was the end of it was getting clogged, so they moved the end of the vent, and you were supposed to attach it around the fuel filler neck. This allows air that has been scrubbed by the charcoal of fuel vapors to exit the system. If it is faulty and stuck open that could be the cause of your leak.

I had added a picture of the charcoal canister as well as a picture of the new updated vent valve as well as an illustration of how a typical EVAP system works. The vent valve usually ends up being the issue in the end on most vehicles that I have dealt with.

I found one on Rock Auto for $40.00. Might be worthwhile to try that. Since it's cheap and probably doesn't have the updated version in it, if it were my vehicle I would just try and replace it and see what happens. Also, depending on what type of scan tool you have, you can command it open or closed.

Also here is an article that might help as well:

https://www.2carpros.com/articles/evap-system-code-repair

I have also added a TSB concerning the vent valve redesign and replacement process as well as the manufacturer's part numbers.

Let me know how it goes and send me pictures of what you've replaced then we can go from there.

Thank you,
Brendon

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