Evap vapor canister

Joined
Dec 16, 2009
Messages
116
Location
Rhode Island
I've had a recurring evap large leak code on my 2013 Impala with the 3.6 LFX engine. I changed the gas cap and replaced the purge valve under the hood, but this didn't fix it. The next step was to try changing the vent valve/vapor canister assembly at the fuel tank. After replacing the canister assembly I took the old one apart out of curiosity. While I'm not entirely sure how these canisters work, I thought they were supposed to contain activated charcoal. Instead, I found grey dust that spilled out of the canister and no charcoal pellets at all:
canister.jpg


I didn't open the new one out of fear of damaging any gaskets or seals it may have on the cover, so I can't compare how it is supposed to look. Doesn't charcoal go in the bottom of that canister around the sides?

I will find out soon if this fixes the evap codes.
 
Joined
Dec 28, 2005
Messages
1,142
Location
Virginia
This is just the vent valve. The charcoal canister is a separate component. It's rectangular in shape and larger, with three tubes/pipes leading to it -tank, purge, vent.

A smoke test will show you where the leak is.
 

WA1DH

Thread starter
Joined
Dec 16, 2009
Messages
116
Location
Rhode Island
No gravel roads, but I have no idea what the last owner(s) drove on.

I ran some fuel tank pressure data logging before and after changing the valve/canister assembly. Here is 2 trips logged before:
Screenshot_2020-09-21_11-30-24.png

Screenshot_2020-09-21_11-32-22.png
...and 2 trips logged after:
Evap Fix 1.png

Evap Fix 2.png

It looks like the evap leak test is now pulling more than double the vacuum on the tank with the new valve and canister assembly. I posted this up and did some reading on Impala Forums and the consensus seemed to be that the vent valve was stuck open.

Just curious, but does anyone know the exact vacuum pressure cutoff in Pa or PSI that the ECU is looking for to trigger the large leak CEL? There is no number listed in the shop service manual, other than stating that it is a, "Predetermined pressure."
 
Joined
Dec 19, 2013
Messages
6,861
Location
Fort Worth, Texas
Large Leakage is determined by the time it takes to reach the predetermined vacuum level when "Sealed & Purged". You can run Seal & Purge tests via a scan tool while monitoring Vacuum Decay.
*This is my first step, If I find a sharp decay....I install a sealed/known good Gas Cap.
*Retest....Still sharp decay?
*Straight to the the Smoke Machine, A good "smoke machine" isn't just that.....It's a Flow Meter as well!!! Which is very/more helpful in my opinion.
 
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