Yet another vacuum leak?

[Infidel Edition]

I changed the fuel filter and when I started it up to check for leaks... I noticed a hissing from above the gas tank!
Where do those lines go and how do I find that leak?

[bigjim350]

Could just be a sound coming from the vent tube maybe.

[Infidel Edition]

Could just be a sound coming from the vent tube maybe.

That would be cool!
I did see a line that goes that way and splits into a 'T' about where the tank has the in/out line for the pump.
...the vacuum lines go up & over the tank somewhere.

[XJ Wheeler]

Some hiss, not sure why. Probably vents like Jim said. The hoses you saw are the vent lines, two on top of the tank.

[ParadiseXJ]

On the top of the tank are 2 vent connectors (roll-over valves) made of plastic. Each has a vac hose attached to it. The 2 vac hoses come to a T and turn in to 1 hose. That hose runs off the top of the tank into some metal tubing. Then the metal hose ends and takes off with rubber hose to your EVAP charcoal cannister. It's there to vent gas fumes to the cannister. They're built so that if the truck rolls...the little float inside shuts the valve, like on a shop-vac, so you don't leak fuel all over.

California smog testing will pressurize the tank to see if it holds the pressure, making sure the system is airtight. When I first got my MJ, the valves were old...and broken. So I failed my first stab at smogging it. My smog guy told me to check the valves, and sure enough they were both broken and the hose was just sitting on the top of the tank.

Went to the dealer to buy two new valves ($27 each). I had to partially drop the tank to R&R them. Problem fixed. I don't think that if those valves are broken that they would actually affect the way the thing runs...you'll just smell gas fumes while running.

[Infidel Edition]

On the top of the tank are 2 vent connectors (roll-over valves) made of plastic. Each has a vac hose attached to it. The 2 vac hoses come to a T and turn in to 1 hose. That hose runs off the top of the tank into some metal tubing. Then the metal hose ends and takes off with rubber hose to your EVAP charcoal cannister. It's there to vent gas fumes to the cannister. They're built so that if the truck rolls...the little float inside shuts the valve, like on a shop-vac, so you don't leak fuel all over.

California smog testing will pressurize the tank to see if it holds the pressure, making sure the system is airtight. When I first got my MJ, the valves were old...and broken. So I failed my first stab at smogging it. My smog guy told me to check the valves, and sure enough they were both broken and the hose was just sitting on the top of the tank.

Went to the dealer to buy two new valves ($27 each). I had to partially drop the tank to R&R them. Problem fixed. I don't think that if those valves are broken that they would actually affect the way the thing runs...you'll just smell gas fumes while running.

Thanks for the reply~

I'm trying to pass Oregon DEQ... And the previous owner said it was "running rich" but didn't know what the code was or any relevant info!

...3 most likely causes generally are (according to a mechanic friend):
1- vacuum leak......................which makes the MAP sensor think there's too much oxigen in the mix and it tries to compensate by adding fuel
2- bad O2 sensor...................which confuses the MAP sensor...
3- bad/wrong thermostat .......which makes the computer try to heat up the engine by cooking more fuel.

I was missing the thermostat and fixed at least 1 vacuum leak. And I was trying to make sure I don't have any other vacuum leaks before I take it to DEQ next week.
** so those 2 lines... are they vacuum? or vent?
If they're vacuum, I may just plug them off till I pass and will find replacement valves down the road at some point.

Thanks again,

[ParadiseXJ]

Thanks for the reply~


** so those 2 lines... are they vacuum? or vent?
If they're vacuum, I may just plug them off till I pass and will find replacement valves down the road at some point.

Thanks again,

They are technically vent lines BUT the fumes they vent are pulled into the charcoal cannister via vacuum. That is probably why when they're missing they don't reall affect the operation of the engine (I never noticed it anyway). When I tried to smog mine the first time, it passed the sniffer fine. It failed the fuel tank pressure test. I don't know the procedure in Oregon.

Some states do an "inspection" for safety purposes and have no emission testing. California does not do a safety inspection (not here any way) but they're a bear on the emissions and OE emissions equipment inspection.

[Infidel Edition]

I don't know the procedure in Oregon.

Oregon (only in Portland metro and Medford metro) have DEQ ~ they basically plug into the computer and match it to "recommended" alerts.
ie. O2 sensor issues, Fuel running rich, other misc. crap.

I used to live in LA county. Graduated Claremont HS... Jr. High in Pamona...
I remember the CA testing on my first car. Less BS and more actual measure than OR does.

At any rate, thanks again. I'm gonna plug the main line just in case.
Then down the road, I'm going to make sure the lines are actually plugged in to the vents. I don't remember hearing that hissing before. But I've only owned it for a few weeks now.