Running lean

[builds4christ]

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]

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]

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]

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]

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.

 

[builds4christ]

Yep you guys got it.

I ran the truck monitoring vent and tank pressure.

The highest the pressure got was .4 mmHG. The vent remained open the entire time.

@mikez71 won't the pump create vacuum though?

Lol, update on fuel pump. I replaced it yesterday and now the truck won't start. It did something funny. So, before taking the tank down, I pulled the fuel pump relay and fuel pump fuse to run the lines dry.

I started the truck and it kept running! Went to the web with this and someone was saying the FSCM was likely internally shorted and I would need to pull it's fuse for it to turn the pump off. Sure enough, it worked.

Now it gets worse. Took the tank down, removed the pump and found a tone of debris in the tank. It was filled with broken down tubing and black tape. The tape was wrapped around the float, which explained the erroneous readings, and the tubing was riddled throughout. It looked as if someone tried to siphon and broke the tube off inside, but I can't make heads or tails of the black tape lol. So I spent a few hours cleaning everything out.

It gets worse.

The new acdelco pump amazing sent me was the wrong one. It didn't collapse enough. Ao I was stuck with a tough decision. It was on a friends lift so I couldn't leave it there too long. So we took the old and new pumps apart, put the new pump and basket on the old harness body, whited everything in and basically made a new pump out of the old one. They're both Bosch pumps and the wire coloring is the same. I can't imagine the polarity is switched on them.

Reinstalled. Crank no start. Disconnected the battery for a minute or so. Nothing.

I'm suspecting the FSCM, but dang, it was working before that.

 

[mikez71]

I haven't heard of the EVAP system measuring vacuum from the fuel level going down..
I have heard it measures pressure increase from the pump heating up the fuel.
But, that's only what I've heard...
I thought when I recorded my tank pressure, it was close to atmospheric pressure..

Sucks about the pump being wrong..
Does the scanner say anything about the FSCM?

At least you got the fuel tank cleaned out!