Can a pressurized tank lead to a fuel delivery issue? (1 Viewer)

[effjay55]

What’s been determined here?

Hey Rush, Well last weekend I did the test you suggest and got some mixed results. I would blow the lowest pressure air into the vent lines one by one and in some cases I could hear a slight gurgling and even some sputtering of some fuel coming out of 1 of the vent lines. But for the most part all of the lines were venting the compressed air fine it seems.

Correct me if I’m wrong but I started thinking there’s probably 4 vent lines because, since the tank is so flat, there’s a possibility one of the 4 corners are inevitably going to be flooded with fuel; that the fuel vapor separator is designed to capture any of this sputtering of fuel and return it back to the tank. So I think the operation of these vent lines are good.

I also did the other tests again (gas cap off) with low pressure air and didn’t hear any gurgling like before.

I did however put everything back together and took it for a test drive , the truck drove great for around 30 minutes and had no misfires, but when I got home and opened the gas cap there was still tons of pressure coming out.

This weekend I plan to try and drive it again , let it build up pressure then i plan on disconnecting the vent line before the check valve to see if it’s just not opening up. What do you think? I have a suspicion it’s the valve. It’s new but maybe the pressure specs are off…?

 

[WarDamnEagle]

Hey Rush, Well last weekend I did the test you suggest and got some mixed results. I would blow the lowest pressure air into the vent lines one by one and in some cases I could hear a slight gurgling and even some sputtering of some fuel coming out of 1 of the vent lines. But for the most part all of the lines were venting the compressed air fine it seems.

Correct me if I’m wrong but I started thinking there’s probably 4 vent lines because, since the tank is so flat, there’s a possibility one of the 4 corners are inevitably going to be flooded with fuel; that the fuel vapor separator is designed to capture any of this sputtering of fuel and return it back to the tank. So I think the operation of these vent lines are good.

I also did the other tests again (gas cap off) with low pressure air and didn’t hear any gurgling like before.

I did however put everything back together and took it for a test drive , the truck drove great for around 30 minutes and had no misfires, but when I got home and opened the gas cap there was still tons of pressure coming out.

This weekend I plan to try and drive it again , let it build up pressure then i plan on disconnecting the vent line before the check valve to see if it’s just not opening up. What do you think? I have a suspicion it’s the valve. It’s new but maybe the pressure specs are off…?

Not trying to insult your intelligence but make sure the check valve is in the correct orientation. You can also take it off and see if you can blow air through it from the upstream side.

 

[effjay55]

Not trying to insult your intelligence but make sure the check valve is in the correct orientation. You can also take it off and see if you can blow air through it from the upstream side.

I did I double, triple, quadruple checked the thing. I also question my intelligence quite often . I did blow around 2-5psi through the intake side and it seemed to work properly and thinking back on it the amount of air i was blowing through it definitely seemed like less pressure than what comes out of the tank when removing the cap, so maybe my test this weekend will be useless.

 

[WarDamnEagle]

Where did you introduce air when you checked the line all the way to the charcoal canister?

 

[effjay55]

Where did you introduce air when you checked the line all the way to the charcoal canister?

The line that attaches to the outtake of the check valve.

 

[bobm]

1 question?? Do you need all dis ??

 

[WarDamnEagle]

The line that attaches to the outtake of the check valve.

View attachment 3838750

Try it from the inlet to the check valve or from one of the four inlets at the bottom of the fume separator. If you do it from there though, you have to plug/clamp the other 3 inlets.

 

[Pighead]

1 question?? Do you need all dis ??

No. But the people who remove it complain about the gas smell

 

[RUSH55]

I did however put everything back together and took it for a test drive , the truck drove great for around 30 minutes and had no misfires, but when I got home and opened the gas cap there was still tons of pressure coming out.

If you feel that you’ve eliminated any potential blockage in the venting system up to the charcoal canister, then the next step is to go through everything on the other side of the canister.
There is a Vacuum Switching Valve (VSV) which is operated by an emissions control computer. Two lines appear to go from the canister to the carburetor, one of which goes to what is called the Throttle Position (TP) Diaphragm.

 

[Pighead]

I did however put everything back together and took it for a test drive , the truck drove great for around 30 minutes and had no misfires, but when I got home and opened the gas cap there was still tons of pressure coming out.

Is that the only complaint? Pressure in the fueltank? That's a normal good thing. I think. Mine does ,always has. doesn't everybody's?
How much pressure is tons of pressure?

 

[effjay55]

Is that the only complaint? Pressure in the fueltank? That's a normal good thing. I think. Mine does ,always has. doesn't everybody's?
How much pressure is tons of pressure?

So heres the previous post with a link to a short video of the pressure escaping. You think this is normal then?

Search results seem to indicate that it can be a bad thing , your tank could crack, fuel can spew out of the filler tube, etc… I wasn’t sure if what I’m experiencing is severe or something to be worried about. But then again I have also read of cases where pressure is escaping for MINUTES, so maybe this is a witch hunt?

I managed to upload a short little clip of it on YouTube. You can hear the “whoosh” when I open the gas cap. Would this be considered normal?

 

[bobm]

Try a different cap . what happens

 

[WarDamnEagle]

If you feel that you’ve eliminated any potential blockage in the venting system up to the charcoal canister, then the next step is to go through everything on the other side of the canister.
There is a Vacuum Switching Valve (VSV) which is operated by an emissions control computer. Two lines appear to go from the canister to the carburetor, one of which goes to what is called the Throttle Position (TP) Diaphragm.

View attachment 3839033

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View attachment 3839036

Is this information in the FSM or in another document?

 

[effjay55]

If you feel that you’ve eliminated any potential blockage in the venting system up to the charcoal canister, then the next step is to go through everything on the other side of the canister.
There is a Vacuum Switching Valve (VSV) which is operated by an emissions control computer. Two lines appear to go from the canister to the carburetor, one of which goes to what is called the Throttle Position (TP) Diaphragm.

View attachment 3839033

View attachment 3839034

View attachment 3839035

View attachment 3839036

Thanks Rush, good idea. Ill start to look at this, this weekend.

Try a different cap . what happens

the cap is new! Might pop the old one back on to see though…

 

[effjay55]

Is this information in the FSM or in another document?

This looks like the Haynes manual

 

[Lifelong40Fan]

Try a different cap . what happens

Amen! Or drill a small pin hole in your cap if you’ve eliminated any blockages in the vent lines.

 

[RUSH55]

Is this information in the FSM or in another document?

Haynes

 

[RUSH55]

Is that the only complaint? Pressure in the fueltank? That's a normal good thing. I think. Mine does ,always has. doesn't everybody's?
How much pressure is tons of pressure?

Not the only complaint at the beginning of the thread. There should be a zero pressure to very little pressure in the tank, that’s what the venting system is for.

 

[bobm]

Me guts a lotta pressure in my tank butt it comes out constantly

 

[effjay55]

So i took off the check valve from the fuel vapor separator and pressure was coming out. Starting to think that maybe this check valve is either faulty, or possibly not really meant for this ‘74 1.5F engine.

I have read that there should be a little bit of backpressure thats why the check valve opens past a certain psi… is this enough pressure that would cause this wooshing im so concerned about?

Thinking maybe just removing the check valve out of the equation, what do you think?

This is the check valve I put in…

OEM Fuel Vapor Check Valve for '75 to '77 Land Cruiser FJ40 FJ55

OEM fuel vapor check valve for 1/'75 to 9/'77 Toyota Land Cruiser FJ40, FJ55. Part # 90917-10020.

www.cityracerllc.com

Maybe Im wrong to assume itll work for the 74… wish there were psi specs somewhere