What did you do to your NNBS GMT900 Tahoe/Yukon Today?

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iamdub

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Anyone have any tips for building more pressure in the lines to evacuate those stupid charcoal pellets without blowing connections off? Should I still try a fill with the tank to canister line disconnected?

Also, when I blew out the purge line from the engine bay, I got pellets coming back out the same way.

I found that very low pressure was far more effective than trying to blast 150psi through the lines. Gently puffing the lines moves the lightweight pellets along just the same as the engine vacuum did. Shotgunning them with high pressure makes them jam hard against each other and form clogs. I removed the lines off the tank and shook them around and beat them on the concrete as I pulsed the air nozzle to break up the jams and blow them out. For the purge line from the engine to the tank, I puffed it back and forth a few times until no more pellets came out.
 

RooTBeeRthe1st

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I found that very low pressure was far more effective than trying to blast 150psi through the lines. Gently puffing the lines moves the lightweight pellets along just the same as the engine vacuum did. Shotgunning them with high pressure makes them jam hard against each other and form clogs. I removed the lines off the tank and shook them around and beat them on the concrete as I pulsed the air nozzle to break up the jams and blow them out. For the purge line from the engine to the tank, I puffed it back and forth a few times until no more pellets came out.
Ok, what am I missing?
What's the deal with pellets in lines and needing to get them out?
 

George B

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I found that very low pressure was far more effective than trying to blast 150psi through the lines. Gently puffing the lines moves the lightweight pellets along just the same as the engine vacuum did. Shotgunning them with high pressure makes them jam hard against each other and form clogs. I removed the lines off the tank and shook them around and beat them on the concrete as I pulsed the air nozzle to break up the jams and blow them out. For the purge line from the engine to the tank, I puffed it back and forth a few times until no more pellets came out.
Low pressure and lots of volume if you can.
 

kbuskill

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Ok, what am I missing?
What's the deal with pellets in lines and needing to get them out?

The pellets are charcoal pellets that get sucked out of the EVAP canister when the cloth "filter" gets breached. This is caused by overfilling the gas tank which soaks the filter material in the canister causing it to break down over time.

The pellets find there way into the EVAP lines going to the tank as well as to the engine's purge solenoid and cause all kinds of issues from not being able to fill the tank because the pump keeps shutting off to EVAP codes for small and gross leaks because they will get stuck in the purge solenoid and hold it open when the ECU commands it to be closed.
 

iamdub

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Ok, what am I missing?
What's the deal with pellets in lines and needing to get them out?

The pack of carbon pellets inside the EVAP canister ("charcoal canister") ruptures and the pellets course through the system. They clog the vents shut and jam the valves from closing. I'm sure age of the EVAP canister has something to do with it. But I'm quite convinced that repeatedly topping off the tank when filling plays a role in the canister's demise. That canister is supposed to capture gasoline vapors, not liquid gasoline. I view it as a tea bag, only filled with carbon pellets instead of ground tea leaves. Soak it too many times with gasoline and it'll eventually rupture.
 

RooTBeeRthe1st

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The pellets are charcoal pellets that get sucked out of the EVAP canister when the cloth "filter" gets breached. This is caused by overfilling the gas tank which soaks the filter material in the canister causing it to break down over time.

The pellets find there way into the EVAP lines going to the tank as well as to the engine's purge solenoid and cause all kinds of issues from not being able to fill the tank because the pump keeps shutting off to EVAP codes for small and gross leaks because they will get stuck in the purge solenoid and hold it open when the ECU commands it to be closed.

The pack of carbon pellets inside the EVAP canister ("charcoal canister") ruptures and the pellets course through the system. They clog the vents shut and jam the valves from closing. I'm sure age of the EVAP canister has something to do with it. But I'm quite convinced that repeatedly topping off the tank when filling plays a role in the canister's demise. That canister is supposed to capture gasoline vapors, not liquid gasoline. I view it as a tea bag, only filled with carbon pellets instead of ground tea leaves. Soak it too many times with gasoline and it'll eventually rupture.
Well thank you very much you two. That makes complete sense. A shame such a minor thing turns into a big problem.
I suppose I don't have that issue, yet...
 

pwtr02ss

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Cv axle boot developed a leak on the avalanche. I replaced that boot prob 60k miles ago. At 200k, it's time to replace the entire assembly I suppose. What axles you guys using? OEM or aftermarket?
 

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