2005 Tahoe gas filling / purge canister - clearing lines of carbon

[tennfire]

2005 Tahoe 5.3 but not flex
Today, we noticed that when trying to fill the gas tank that the system is not working as normal and the gas pump keeps kicking off after 1/2 gallon or so unless you fill it very slowly. Reading on this site it seems like culprits are problems with potentially evap solenoid, evap canister, purge valve, wiring to solenoid, and/or plugged lines servicing these components.

The posts I have read indicate that the solenoid, canister, valve are all relatively straight forward parts replacements.

But, there are comments in some posts about needing to clear clogs potentially from the lines. Some indicate dropping the tank but I wanted to ask, since this will be a one-man driveway job if I undertake it in what is presently high temp, high humidity summer of Tennessee, if the lines can be cleared with an air hose without having to remove the gas tank.

It seems there is a line from the purge valve (on the engine) to the rear and at least 2 lines from the tank. One comment on a Youtube video asked if it was possible to clear the lines with the canister, solenoid and valve all disconnected before reinstall. The question asked about blowing the line from the valve with air pressure and then using a shop rag to assist in blowing air into the tank's filler neck to clear the other two lines.

 

[Fless]

Be sure you're turning off the engine while fueling; this turns off the command that closes the canister vent valve (so then it's open with the ignition off). If you have access to a bi-directional scan tool, that can help to command the various valves open and closed. These are very simple systems but the various symptoms can confuse the heck out of many of us.

And don't get ahead of yourself -- start with opening up the lines at the canister. You may or may not find that the pellets have escaped. Using a hose you can try to blow a little mouth air through the canister to see if it's clogged/plugged, and the same with the canister vent valve. That one can be tested by alternately applying 12v to the terminals; doing that should close it, but it should be open without any voltage. Many times one or both of those parts is the issue.

At that point you can shoot some gentle air from the engine side to see if the line back to the canister is open.

See https://www.tahoeyukonforum.com/thr...ge-valve-just-do-extra-pm.130637/post-1630681 and @iamdub may have more to say about it since his carbon constipation was pretty extreme.

Eric O at South Main Auto (YouTube) has a few good videos on testing the canister vent valve, so let us know if you have any trouble finding one. Here's one that could be of interest:

 

[tennfire]

Thanks! Nope on the scantool but I think I saw one video on testing the sensors. But they are also 17 years old, have apparently an internal filter on the solenoid and relatively cheap to replace if you have it otherwise taken apart.

That is a good point on the pressure/CFM for trying to clear the lines versus compressing
the blockage. Easy enough to crank down the regulator.

Mainly trying to see if this is a project doable without taking the tank out. If that is required, this may end up at a local shop that I trust.

 

[Fless]

It would be easy enough to investigate and do some diagnosis before taking it to a shop. At least you'd know if the canister is/isn't plugged, or the vent valve is/isn't working properly.

 

[iamdub]

2005 Tahoe 5.3 but not flex
Today, we noticed that when trying to fill the gas tank that the system is not working as normal and the gas pump keeps kicking off after 1/2 gallon or so unless you fill it very slowly. Reading on this site it seems like culprits are problems with potentially evap solenoid, evap canister, purge valve, wiring to solenoid, and/or plugged lines servicing these components.

The posts I have read indicate that the solenoid, canister, valve are all relatively straight forward parts replacements.

But, there are comments in some posts about needing to clear clogs potentially from the lines. Some indicate dropping the tank but I wanted to ask, since this will be a one-man driveway job if I undertake it in what is presently high temp, high humidity summer of Tennessee, if the lines can be cleared with an air hose without having to remove the gas tank.

It seems there is a line from the purge valve (on the engine) to the rear and at least 2 lines from the tank. One comment on a Youtube video asked if it was possible to clear the lines with the canister, solenoid and valve all disconnected before reinstall. The question asked about blowing the line from the valve with air pressure and then using a shop rag to assist in blowing air into the tank's filler neck to clear the other two lines.

As Fless said- USE LOW PRESSURE! Shotgunning it with 100+ PSI sounds fun, but it makes matters MUCH worse.

There are two vent systems at play here. One that's high volume for when you're filling up and another that's very low volume to purge the collected fuel vapors from the charcoal canister and let 'em get sucked into the intake manifold to be burned off. If it's clicking off when filling, that's a problem with the tank vent. There's a large vent hose that runs from the tank to the charcoal canister. There's three hoses on that canister and it'll be the largest. You might have to drop the spare to access it. Push inward on the connector as if you're trying to push it harder onto the nipple, squeeze the tabs to unhook the barbs and slide it off the nipple. You might have to use a small screwdriver to help get the barbs over the ring on the nipple. See if any pellets come out when you take it off. With it off, you should be able to fill up as normal.

The other two connections are the hose to the intake manifold and what we can call the "fresh air inlet", which is on a valve (vent solenoid) with a hose off of it that runs up the filler neck just to have a protected high mounting point. Pop off the hose that runs to the intake manifold. If pellets are present, then pull the hose off the purge solenoid on the intake manifold to check for pellets there. This is the hose you wanna lightly puff air through to gently coax them out of the line. I never thought about it and went all power monger and put 150+ psi in mine. Some pellets came out with that first blast, but then it acted as if it had a hard clog. Yeah, I did that. The pellets shot so hard and fast through the pipe that they wedged at the first turn and compacted. I had to beat the lines front to back and puff it with the air in both directions for quite a while until no more pellets came out and I could blast full pressure through both ends with no restrictions.

If there are no pellets, that vent solenoid valve might be stuck closed.

I'm betting your charcoal canister is clogged and just due for replacement. For the relatively minimal cost, I replaced the vent valve while I was under there and had everything apart.

 

[treehan77]

I tried blowing my lines out - there were charcoal pellets all the way up to the purge valve under the hood lol. While I was able to get some out, I ultimately had to drop the tank in the driveway to fix it completely.

 

[iamdub]

I just proofread my novel and found that it might be a little confusing. I shouldn't write after sundowning.
Just ask if you need any clarification on my ramblings.

 

[iamdub]

I tried blowing my lines out - there were charcoal pellets all the way up to the purge valve under the hood lol. While I was able to get some out, I ultimately had to drop the tank in the driveway to fix it completely.

Same!

I cleared the pellets and replaced the canister and vent valve but would still get an intermittent code for the EVAP system. When I dropped the tank to replace the fuel pump (unrelated issue), I found more pellets. I ended up removing that whole mess of piping off the tank and beating it on the concrete while I shot air through it. Hosed out the tank and cleaned the purge line once more and reassembled.

Then I immediately had the same issue when filling, but for a different reason this time. When I put the tank back in, I didn't route the vent hose OVER the cross member. It was crushed between the tank and cross member, making it vent less than when the canister was clogged. I had to add this in here for anyone else reading just so they'd already know about that hose when putting their tank back in.

 

[Fless]

When I put the tank back in, I didn't route the vent hose OVER the cross member. It was crushed between the tank and cross member, making it vent less than when the canister was clogged. I had to add this in here for anyone else reading just so they'd already know about that hose when putting their tank back in.

Understood for other eyes. The OP's is an '05 so I don't think the evap line goes over the xmember. I could be wrong; it didn't on my '04 but it's Flex.

 

[treehan77]

The AC Delco valve in the rear installed didn’t work at all either-it was defective. Easy to test, which I did on the next replacement lol