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I discovered a fuel leak on the bottom of the EVAC canister of my 1971 Corvette. The hose was very loose and easily pulled off after which a volume of gas poured out.
Is it normal to have gas in the EVAC canister? I though this was only to control fumes?
Yup. I suspect the vapor separator doohicky on the upper driver corner of the fuel tank. Not fun to get to but just a bolt on part that you can change out without draining the tank (as I recall).
Have you changed out your gas cap recently?
I discovered a fuel leak on the bottom of the EVAC canister of my 1971 Corvette. The hose was very loose and easily pulled off after which a volume of gas poured out.
Is it normal to have gas in the EVAC canister? I though this was only to control fumes?
Thank you for your input.
Alan
There should be a fuel separator valve mounted on your fuel tank that is supposed to prevent gas from getting to the canister while allowing fumes to flow through the line. Sounds like that valve has failed. Unfortunately the aftermarket valves are pieces of junk to the point I believe they are dangerous. They frequently open up at the seams and allow fuel to drip on the mufflers or they fail internally which prevents the valve from working and allows fuel into the vapor canister line when the tank is full. Here is a thread I started about the subject: https://www.corvetteforum.com/forums...e-problem.html
My thoughts also, just was hoping something that wouldn't be such a chore to deal with.
I believe it requires removal of the tank?
I was able to change the fuel separator valve in my '73 without dropping the tank but it was a one handed blind operation. If your muffler is fairly easily removed, that creates a lot of space to make the job even easier.
Seconds on Roy W. comment. I usually fill my tanks to the tippy top for winter storage to get rid of extra air and condensation. Well I overfilled it and it came out thought he cannister. I would check that first. Ike
Roy W-what is too full? I fill my tank to the bottom of the filler tube. Are you saying the fuel drains into the vent line at that time? Fuel is drawn into the EVAC canister and leaks out the bottom at 3/4 and 1/2 tank after an hours drive. Shouldn't the fuel separator valve prevent this?
DC-I read your previous thread with great interest and felt your frustration! I've looked online at that fuel separator that you posted and my first thought was "plastic junk". Where are you at with your journey? Did you end up going with a vented gas cap and sealing off the system?
Like you my mufflers are welded, just installed Flowmaster 44's and hope not to cut them loose.
Roy W-what is too full? I fill my tank to the bottom of the filler tube. Are you saying the fuel drains into the vent line at that time? Fuel is drawn into the EVAC canister and leaks out the bottom at 3/4 and 1/2 tank after an hours drive. Shouldn't the fuel separator valve prevent this?
DC-I read your previous thread with great interest and felt your frustration! I've looked online at that fuel separator that you posted and my first thought was "plastic junk".
Just to be fair, the original GM product feels like plastic junk too. There really isn't much to it. As I recall, it's located on the top-front driver corner and plumbed from near the top-center of the tank. A full tank could certainly put the valve to work, but at 3/4 and 1/2 tank there should be little fuel slosh to get up there unless you're really throwing it into corners - like during autocross.
Don’t quote me. But if you fill the tank to the neck of the tank that will put the volume in the tank above the plastic separator. Then there is a good possibility that it will leak into the canister. Easy enough to test. Don’t fill the tank as high and see if your leak stops. Ike
DC-I read your previous thread with great interest and felt your frustration! I've looked online at that fuel separator that you posted and my first thought was "plastic junk". Where are you at with your journey? Did you end up going with a vented gas cap and sealing off the system?
Like you my mufflers are welded, just installed Flowmaster 44's and hope not to cut them loose.
This is really getting interesting!
Alan
See the last 4 posts in my thread I linked to. I converted to a rollover valve that came with my new Tanks Inc. tank when I went to fuel injection. I am running a sealed gas cap with that valve along with a '74 + charcoal canister and I have no gas smell in my garage.
Don’t quote me. But if you fill the tank to the neck of the tank that will put the volume in the tank above the plastic separator. Then there is a good possibility that it will leak into the canister. Easy enough to test. Don’t fill the tank as high and see if your leak stops. Ike
No. As I mentioned in my thread and in a post above I can get fuel into the vapor canister with only 3/4 of tank of gas when the fuel separator valve has failed. It doesn't matter how much fuel you put in the tank if the separator valve is working properly. That is its purpose - to keep fuel out of the canister line.
It is also possible that the vapor canister is capturing the fuel vapors, but is not purging them due to a defective vacuum switch on the canister or due to a lack of vacuum signal to cause the canister to purge the vapors. Eventually, the charcoal in the canister will saturate and start dripping out the bottom.
A defective fuel separator gizmo and overfilling the fuel tank could also cause raw fuel to enter the cansister.
Last edited by 7T1vette; Mar 23, 2021 at 12:35 AM.
I'm guessing the OEM tank sits higher than the canister...if anything/part fails....the canister becomes a siphon/molotov cocktail when the canister vacuum switch engages???
I removed my tank and was able to take it down with out moving the mufflers. I just needed to bring it down on an angle. It would be a good time to change all the hoses and the gasket for the filler neck.
My filler neck was leaking all over the top of the tank.
It's been great to bring this issue to the forum and I appreciate everyone's advise, insight, photos and suggestions!
I'm in process of doing some additional research, namely the easy ones to begin with of replacing the gas cap and not filling the tank so full. I'll be reporting back in a few days with my results.
Interesting thread. Having just recently jumped back into C3 ownership with a 73 I have spent the last few weeks unsorting past misdeeds. While I knew what the separator valve was having owned a 71 project car in the past it wasn't until I read DC's thread on the subject I fully understood how the EEC system works. So far no indication my system is not functioning but something I will be mindful of going forward.
Between Evaporative Emission Control (EEC), Exhaust Gas Recirculation (EGR), Transmission Controlled Spark (TCS), Air Injection Pump (AIR), Diverter Valve's, Check Valves etc. you have to wonder if GM was just throwing spaghetti at the wall to get over the EPA rules of the 70's without putting a lot of thought into the engineering.
Case in point this week was TCS 101 education while I'm waiting on my rebuilt Q-Jet (thanks Lars) to arrive. I was headed down the road of putting this system back operational but once I fully understood all the components and the theory of operation I was like no way I want that system operational and why would GM do that. EPA I'm guessing.
As pointed out in DC's thread there is no Fuel Vapor Canister available for 73 and older cars so I may have to start the hunt for a good used OEM spare and might as well starting hunting for a good used OEM seperator.
Fuel Leak
