Running lean

builds4christ · Tuesday at 8:35 AM

I get what you're saying.

I wouldn't mind venting it to atmosphere, but was honestly unsure about which line to disconnect.

The truck had a lean problem initially, until I discovered a huge vacuum leak at the MAP. Then it decided it would go rich. So a rich condition is my most recent battle.

The PCM was modified not to purge, as far as I can tell. You may be on to something though. I wonder if it is venting properly. Even if it's not the reason for my current issue, it's still something I should address.

Isn't there some way to vent the tank to atmosphere, but THROUGH the canister to prevent the smell?

rdezs · Tuesday at 8:52 AM

Go down by your carbon canister and locate your vent valve solenoid. You'll see it vents up a rubber hose that goes up by the fuel filler neck. Just take the vent valve solenoid out of the equation, retaining the hose that goes up by the filler hose.

rdezs · Tuesday at 9:00 AM

The piece that's at the end of the hose is basically a screen made from plastic. What's disconnecting the hose from the vent valve solenoid, you can simply blow through it to make sure it's free-flowing.

dkad260 · Tuesday at 9:41 AM

builds4christ said:
Isn't there some way to vent the tank to atmosphere

I'm not 100% but generally at some point the tank needs to hold a vacuum....so a full-time vent is not good. Not sure on the GMT-900 but usually after start, the PCM will close the vent solenoid I believe and pull a vacuum and test the tank...if it will not hold a certain vacuum for a set length it will throw a code.

mikez71 · Tuesday at 10:50 AM

But with the purge valve unplugged it won't pull vacuum.

You can just unplug the electrical connection to vent valve, as it's normally open. (to vent tank pressure)

Either way you'd have to disable the codes, which probably is done since it was tuned not to purge.

Running lean

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