Runs real negative trims with the gas cap off too. Really thinking my can was flooded. As soon as I disconnect the tank from the canister or the purge valve from the canister it runs so much better. Not sure what filtering it actually does, but doesn't seem to be doing it anymore. I might pick one up from a junk yard to see if I can get a different result with a different can, but I can't imagine they would be in much better shape. I'd use the one from my other blazer, but it seems a little annoying to get to and don't wanna have both blazers in pieces lol.

 

If you are not wanting to replace the cannister, there are you tube videos for replacing the carbon in the existing one.

George

 

I might go that route then. I just wish I could figure out a way to actually test it. I'm still not so sure I'm not just creating a vacuum leak that cancels out the extra fuel that could be coming from elsewhere.

 

I thought the trims were normal with the purge valve turned off or disconnected and the port sealed?

George

 

Oh yeah, removing the purge valve and sealing up the hole did make it trim normal. Doing that feels so long ago. Now I'm really thinking the can is bad.

 

Its either a flooded cannister, leaking fuel tank/cap, improper purge opening, and/or a restricted vent line/solenoid. If taking off the gas cap makes the trims double then the tank and cap are probably ok.


George

 

I should be able to blow through the vent line with the car running assuming it's not in a test cycle right? I guess I'll try that then go canister route if that blows clear.

 

Yes, with the vent solenoid electrically connected then its should be open from the vent line at the cannister fitting to the outside air.


George

 

Les helped us out since he is the resident ODB scanner expert. He found purge valve % in Car Diagnostic Pro in case you want to be able to monitor this to help with your diagnosis. Thanks Les.

I experimented further on the Blazer today. Closing the vent solenoid with the tank open has a minimal effect on trims. Opening the tank did but not as dramatic as on my GMC, maybe 5 trim points but my trims are generally higher on the Blazer to start with. Interestingly my trims were a lot higher on the Blazer today as it went through its purge ramp, around -25% but looked the same after the cycle and the purge valve settled back down to it steady state level. Trims were around -8% today after everything settled down.

This whole exercise has been very interesting. I have a three hour drive next week in my 2006 GMC so I will monitor to see what the computer does with these valves over a long drive cycle.

George

 

Still going at it like a caveman out here just poking and plugging and seeing what changes. I had what I think is an interesting result.


With the entire evap system connected, I unhooked the gas tank from the canister. After a few moments I placed my finger over the gas tank port on the canister to plug it. As soon as I plugged the port, my trims started nose diving negative. I then released my plug from the port and trims started going back positive. Where could the extra fuel be coming from now if I've disconnected the gas tank from the canister?