The fuel tank must hold pressured vapors?

[mikyrc]

Just a quick question, when you open the gas tank filler tube cap, you should hear pressured vapors escaping right?

Few months ago the car stopped doing that. Now everytime y unscrew the filler cap it doesn't comeout pressure anymore and sometimes i smell gas on the rea rarea of the car.

Something must be wrong right?

 

[DSMunknown]

Hey mikyrc! Long time, no see.

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Read through this thread or this thread for some good info.

 

[mikyrc]

Hi Anthony.
Yep long time since my last visit.

Thanks for the links but i couldn't find anything that helpedsolving the problem. Altough it helped me understand that there must be some pressure there. Thanks man.


I checked today to put some air pressure through the canister hard line (on the firewall side) that comes from the fumes line on the tank and i could hear air escaping sound on the tank area, but not shure where exactly.
I must have a leak somewhere (altough it doesn't leak drops of gas).

Can a gas filler cap fail even if the seal seems ok?

 

[Defiant]

A failed cap will throw a CEL. The amount, if any, of fuel tank pressure will wander all over depending on weather, temperature, fill level and even seasonal gasoline formulations.
Stop thinking about it.

 

[mikyrc]

Ok I didn't know about a CEL when the cap is failing, thanks.

But what about the gas odor while driving with the sunroof open or when stoping the car after a ride, around the rear bumper/rear wheels area?

 

[DSMULATOR]

It sounds like you have a leak somewhere. If your really concerned about it, pull your rear seat out and there is an access panel to get at your fuel pump and sending unit. Have someone pressurize the line like you did before and sit in the car and see if you can find the leak. It may help to spray some soapy water so that it makes bubbles. Don't be too overzealous with the water otherwise you'll leak it into the tank and will be able dry gas with your next fill up. If you got to pull the sender, then its time for that Walbro 255

 

[mikyrc]

I'll try that thanks!

 

[99gst_racer]

A failed cap will throw a CEL.

How does that work?

 

[Mikelb]

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That's a diagram of a gas cap. The cap has safety valves in it to prevent the tank from building up too much pressure. When these valves deteriorate/break, the cap can no longer keep pressure in the tank, therefore it is like the car is losing gas. (in the form of vapors)
The ECU notes the pressure drop, and it causes a CEL (IIRC).

For more interesting Emissions lessons, check this out:
http://www.dsmtuners.com/forums/showthread.php?t=224901

But what about the gas odor while driving with the sunroof open or when stoping the car after a ride, around the rear bumper/rear wheels area?

Are you running rich? is your exhaust leaking? do you have a catalytic converter?

 

[99gst_racer]

The ECU notes the pressure drop, and it causes a CEL (IIRC).

Via which sensor?

 

[Mikelb]

Via which sensor?

I'm sorry, I wasn't thinking when I wrote that. IIRC, the ECU would note a change in the vacuum in the EVAP system. I misplaced the article I was going to quote, but I'll post it as soon as I find it.

 

[mikyrc]

Are you running rich? is your exhaust leaking? do you have a catalytic converter?

HEy thanks for the schematic.
In fact i thought it could be a cap problem but i tried to blow through it with my mouth and i couldn't so i guess the main presure valve does work.

About the gas smell and richness, i don't use cat and at wot i run 10.5-11:1 but it does smell even after running in closed loop mode 14.7:1 AFR. So it must be a real leak.

 

[Mikelb]

HEy thanks for the schematic.
In fact i thought it could be a cap problem but i tried to blow through it with my mouth and i couldn't so i guess the main presure valve does work.

You're going to need a lot more pressure than your mouth to blow through that cap. The relief valve is a last resort in the system. It only opens under high pressure. Do you still have your charcoal canister in place?

About the gas smell and richness, i don't use cat and at wot i run 10.5-11:1 but it does smell even after running in closed loop mode 14.7:1 AFR. So it must be a real leak.

You're always going to have some smell of gas then, the cat burns off the unburned gas. Mine smells rich when I'm sitting still too... 2.5" pipe, no cats (on my FWD, 3" on the AWD)

 

[mikyrc]

I didn't touch the evap system at all. It's all stock.

And the cap test was only to see if it was leaking, just to eliminate some possibilities.

I don't know Mike, it's real gas odor, not the unburned fuel mixed with exhaust gases.
But it could be.
I'll do a test to see if the tank does hold certain amount of pressure, if it keeps losing pressure by itself, then there's a problem somewhere for shure.

 

[Mikelb]

Might want to check the gas tank seal. It sits down below the filler neck and attaches to the tank.

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[Defiant]

One of the smog checks out here involves putting the gas cap on its own tester. A leaking cap will fail your smog check.

 

[mikyrc]

Guys i'm still on this.

Today i've done a test that made me guess what's wrong. OR at least where to look at.

I've pressure tested the fuel tank and listened for air escaping. And i've found a notticeable air leak noise around the rear of the fuel tank.

The only thing it can be is the fuel cut-out valve, that is located on top of the rear part of the tank. As i checked the fuel filler and vapor hoses and all were ok.

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What do you guys think?
Does anybody ever have had a problem with this valve?

The bad thing is that i'll have to drop the fuel tank.

Do you know if it's heavy?

 

[Defiant]

That valve is supposed to keep the tank pressure within some kind of spec. First thing to do is pull the back seat, remove the pump access cover and see if you can find signs of gas leaks- they're obvious by how much dirt they hold.
Odd that you'd smell it through the sunroof. I'd expect the source to be further forward.
The tank isn't all that heavy when empty (eh, forty pounds?), it's all the damned crud it and all its hosing will be dumping in your eyes and nose.

 

[mikyrc]

That valve is supposed to keep the tank pressure within some kind of spec. First thing to do is pull the back seat, remove the pump access cover and see if you can find signs of gas leaks- they're obvious by how much dirt they hold.
Odd that you'd smell it through the sunroof. I'd expect the source to be further forward.
The tank isn't all that heavy when empty (eh, forty pounds?), it's all the damned crud it and all its hosing will be dumping in your eyes and nose.

I already checked the fuel pump and fuel gauge gaskets and all the hoses around and everything was ok. No leaks. It has never leaked gas. I even sprayed soapy water on them and there wasn't any bubbles.
In fact while listening through the hole left after taking the fuel gauge unit access cover, you can hear the sound coming from further inside, towards the rear of the tank.

About the sunroof, i think i didn't explained very well. The odor isn't coming through the sunroof. The thing is that when i tilt the sunroof and keep the windows closed, the air creates a vacuum through the sunroof and vapors are sucked through the small openings on the rear seat i guess and that's why it smells gas inside the cabin. But only in that particular moment. And also if you smell just under the car next the rear passenger wheel after a ride, you smell gas a lot too.

Thanks for the info about the wheight. I guess that when removing the filler hose a lot of gas will poor out right?
Even if the "low gas" warning light is lit on the gauge cluster, right?

 

[mikyrc]

Hi guys i found the problem:

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As you can see there was a crack on the cut-out fuel valve as i was suspecting.

I cleaned it very well, used some sand paper and aplied a two component glue on it. I think it will work and will never leak again.

So problem solved.

 

[FORMONTOYA]

Nice showing of persistence, which will most always pay off. Thanks for letting us know what the fix was.

 

[DSMunknown]

Thanks for the photo too. The archives will appreciate it (that is, if it doesn't morph into the egregiously hated X).

 

[mikyrc]

You're welcome guys.

 

[Defiant]

Holy crap. What a sonofabitch to diagnose. There's other words I was using (in concert) but the filter here won't let the ####ers through.

Nice fix.

 

[xomega]

know this is a old post. but i found the exact same problem and crack in the exact same location today!