where is the liquid check valve? (evaporative controls)

[elskeptico]

My 79 Chief failed the new CA evap portion of the smog test. I didn't know they were testing it now, so it wasn't really hooked up.

Now that it is hooked up, there's crazy pressure building in the tank, which could only mean it's not venting through the charcoal canister like it should (right?). I've checked the canister, looks good and that filter on the bottom isn't clogged or anything.

So now I want to check my liquid check valve, but I don't know where it is. It's this thing:


I've been all over and under my Jeep and have never seen this thing. There's that weird-looking thing that's inside the left-rear fender well, but it doesn't look like this. Is that the roller-over valve? Am I supposed to have both?

Thanks for any help. I'd love to get it smogged this weekend.

BTW: my Jeep has the auxiliary trailblazer tank with an electric pump.

[beloth]

Originally Posted by elskeptico

My 79 Chief failed the new CA evap portion of the smog test. I didn't know they were testing it now, so it wasn't really hooked up.

Now that it is hooked up, there's crazy pressure building in the tank, which could only mean it's not venting through the charcoal canister like it should (right?). I've checked the canister, looks good and that filter on the bottom isn't clogged or anything.

So now I want to check my liquid check valve, but I don't know where it is. It's this thing:


I've been all over and under my Jeep and have never seen this thing. There's that weird-looking thing that's inside the left-rear fender well, but it doesn't look like this. Is that the roller-over valve? Am I supposed to have both?

Thanks for any help. I'd love to get it smogged this weekend.

BTW: my Jeep has the auxiliary trailblazer tank with an electric pump.

that gizmo is the roll over check valve according to the illistrations in my 73 TSM....atleast that is what the picture looks like....

[tgreese]

Originally Posted by beloth

that gizmo is the roll over check valve according to the illistrations in my 73 TSM....atleast that is what the picture looks like....

No, my parts book says that's a liquid check valve, and that type was not used in 1979.

There's a rollover check valve (smaller, different shape, different connections) next to the fuel filler hoses somewhere. The parts book does not show a liquid check valve at all for that year.

'78 and '79 are the same, so one of those FSMs might tell you more. Lots of hoses in the filler area, but it's not clear from the parts book where some of them go.

[Tornado230]

The liquid check valve prevents fuel from getting into the charcoal canister.
Provides free passage of vapors.
There is a needle and seat and a float within the valve.
Not sure where it is on mine. Will have to look.
If everything is hooked up, you will notice some pressure build-up when removing the gas cap, especially when it is hot. Gas cap has a 2-way relief valve.

[elskeptico]

Thanks for all the replies. I found my valve (rollover, not liquid), and it's not the plastic type that I had in the pic (I should have mentioned that wasn't my pic). Mine is right above the left-rear wheel well, and it's like a little gold tin can with two flare fittings. I just took it out and hooked the two lines together for the smog check, and PASSED

I will post pics of the valve tonight. I bet a lot of folks in CA are going to be looking for this valve soon since they're testing the evap system now.

I still seem to be building up quite a bit of pressure in my gas tanks though. The line that carries the vented vapors (from the back of the Jeep where the rollover check valve is to the engine compartment where the charcoal canister is) seems very small to me. I wonder if it's inadequate to for venting both the stock tank and the auxilliary tank. Maybe I should run a bigger line? Is the pressure in the tank much of a problem?

The input at the canister is much bigger in diameter and could accomodate a bigger line.

[Tornado230]

You are finding out that the emission system in relation to the evaporative controls is set up for the stock fuel tank.
It was not designed to handle the extra amount from the auxiliary tank.