04 Blazer DTC P0455 EVAP resolution? perhaps!!

Well I got the time to look at the wife's Blazer. I pulled the vent solenoid, passes air until energized then blocks air flow, de-energize and the flow is blocked until pressure is off, the it's pass through.
Next I removed the canister for inspection. Looked OK, cap off ports and it held pressure. Next I pressurized the tube into the fuel tank, it held ppressure just fine..... Since the purge valve on the intake manifold and somewhat burried under heater hoses, and wiring harnesses, I opted to just ohm check it and then clip 12 volts to it like I did to the vent valve to see if I could hear it acuate. Sure enough it sounded like it was working just fine. I also removed and re-attached the cap on the test port next to the purge valve.... I fiured my only choice was to remove the valve from the manifold for inspection, or make an appointment at the GM dealer!! So, on with an oil and filter change. After the O & F change, I started it up and let it idle for a while (about 5 minutes) while I cleaned up, dumped the oil into my recycle holding tank etc. Came back to the truck and to my suprise (and delight) the SES light is out!!! Let me say that is real light gauge wire they are using for the solenoids even though they only pull 1/2 an amp!!!! So, what did I do to fix it??? Free up a stuck purge valve??? I don't think the cap was loose on the test port...
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snipped-for-privacy@farm.net wrote:

Bear in mind, I haven't looked up the full code description and code set criteria... There should have been a shraeder valve under the test port cap so even if the cap was loose, it wouldn't have mattered. FYI the shraeder valve is left hand thread in case you feel inclined to snug it up... Exercising the purge valve may have allowed a piece of debris to dislodge but a stuck/blocked open purge valve is usually accompanied by other symptoms like a hard restart after refueling.
The curious thing is the vent valve, when you de-energized it, it should have passed air. I suspect that this is where your problem lies. Ever get a whoosh when removing the gas cap?
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No, no "woosh", but like I said, de energize the coil and it would not pass air until the pressure was off, then it seemed that the solinoid would open. I didn't think of it, but I pressurized the tube from the canister to the purge valve with no leak, so the cap / shreader valve was air tight.... Left handed thread..... how quaint!!! It has always been easy to start, so I dont think the purge valve was stuck open. I still can't get over just how small the wires are!!!!! (I realize the solinoid is 24 ohms so it only pulls 1/2 an amp..... but still!!
On Mon, 23 Jul 2007 11:47:43 GMT, aarcuda69062

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snipped-for-privacy@farm.net wrote:

Probably knocked a piece of dirt out of the vent valve. That or the air pressure you used reseated the plunger and freed it. Keep in mind that that valve doesn't hold pressure it stops vacuum.
The way the system test works is kind of simple. When commanded the vent solenoid closes and the front purge valve opens. This allows the vacuum from the engine to create a vacuum in the tank/lines and vapor canister. Then the computer closes the purge solenoid and times how long the vacuum holds in the system. If it holds for a set time it passes the check, if it doesn't hold the vacuum it fails.
--
Steve W.
Near Cooperstown, New York
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Right, but it was easier to use lung power to pressurize for a quick test than it was to dig out my vacuum pump and adapt tubing to it!!!
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