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Vapor Canister Saturated With Fuel

festx

By festx
in Ask A GM Technician

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festx Enthusiast

festx

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Friday I noticed a very strong fuel smell coming from my 1986 Suburban C10. I popped the hood and saw that gas was dripping from a fitting on the air cleaner vacuum line. I trace the line back to the vapor canister. When I disconnected the line from the vapor canister it was under high pressure and gas spewed everywhere. I quickly reconnected the line so that fuel wouldn't continue to go everywhere. I know that the fuel tank vents into the canister so I slowly opened the gas cap. That too was under higher pressure than usual (lots of hissing). I cant remember the last time I filled the tank completely so I know it's not the common over-filled fuel tank problem. All the vacuum lines appear to be hooked up with no leaks. I'm wondering if it's just a matter of replacing the purge valve and canister, but before I drop $150 I thought I'd just throw this post up to see if anyone has experienced a similar issue.

festx Enthusiast

festx

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Ok, after some tinkering around, here's what I think is happening. I started the suburban and drove it around until warm. I popped the hood and pulled the hoses from the canister one-by-one. The PCV hose was dry (expected), and the carb bowl hose was also dry (which means the carb is not the source of the fuel in the canister). When I pulled the air cleaner hose off the canister gas was spitting out, so this means the source of the fuel is the gas tank vent hose (the only hose I haven't pulled yet). When I pulled the gas tank vent hose, I observed vapors only coming from the hose, not liquid gasoline. I think the purge valve or canister is malfunctioning, or both, causing the vapors to condense in the canister rather than purged and re-burned by the engine. I'm going to replace the purge valve and the canister this week. Unfortunately, these parts are not carried by local parts store, but I found the purge valve for $10 and a new canister for $37 on rockauto.com. The only other thing that I can think of that might be causing this is a bad fuel tank cap.

festx Enthusiast

festx

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Put a new fuel tank cap on it.

 

No dice. I just changed the fuel tank cap and it's still happening. High pressure building up in fuel tank and the canister is saturated again.

festx Enthusiast

festx

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As mentioned in my previous reply, replacing the gas cap did not resolve the issue. It was worth a try though. It was only $8 and the gas cap that was on there looked the original. Anyway, before I drop some more $ trying to resolve this issue, I just want to confirm that what I am looking at under the hood is what I think it is. The Haynes manual does not have an picture of the purge valve and it's location is not clear to me.

 

20110412-kysrgj3c13s62cb2xwkwx2wa43.jpg

 

- What is #1?

- If #2 is the decelerator valve, then is the purge valve built into the vapor canister?

- Is #3 the Thermal Vacuum Switch? If so, is it possible that it's malfunctioning preventing the canister from being purged causing the fuel vapors to condense?

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