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Gas Venting issue

D

devildog0

NAXJA Forum User
Location
Hunt County Texas
I have a 97 that is a california model. Yesterday while climbing a steep hill in 4 low we smelled a strong fuel smell. When we got the top of the climb we checked it out and apparently the pressure in the tank was so great that it actually forced fuel out past the seal on the gas cap.

I know on cali models the tanks are supposed to vent to the Charcoal cannister but this doesn't seem to be happening? Is there supposed to be a vented camp on there? Not on cali models right? Would it throw a code if I put on a vented cap?

Thanks,
Josh
 
If that only happens on steep hills, I wouldn't worry about it. If you think it is problem, buy a new genuine Jeep gas cap. The charcoal canister is for fumes, not liquid fuel.
 
Not on any models.
There are vents on top of the tank connected to a collector on the backseat bump up. As Tim said, they are for fumes and probably don't react well to liquid fuel.

As far as I know, the system is closed loop and pressure is self regulating.
There is no vented cap because that would cause vapors to escape.
Putting one on will cause a CEL.

If gas dribbled past the existing one, my 1st thought, since you were climbing a steep hill, is that it didn't seal well.
X2 on the Genuine Jeep gas cap.

-Ron
 
Ha haven't been able to find one, even Omix-Ada and Rock Auto carries the same STANT cap that's on it now. Here's apicture of what it looked like. Everytime I take the cap off there's pressure venting for a good 10 or 15 seconds.

Keep in mind we went from 400 feet to 8000 feet during the trip so the pressure in the tank would have been higher than normal, since the atmospheric pressure dropped. Look under the gas cap at the wet spot.

10341737_10204722000756025_7877967082634384786_n.jpg
 
There are two rollover valves on top of the tank, the two attached rubber vac lines T into one and go into a steel line, then into a rubber line and into the charcoal, purge valve, whatever. In CA these need to be in place so that fuel vapors do NOT vent into the air, they're supposed to be burned up through the system.

The valves can be broken, the tops are made of plastic, the lines can be disconnected allowing fuel to slosh out. You'll fail your smog test just with the tank pressure test (at least in CA) if that loop is not complete and all the vac lines are in place.
 
I'm sending the paperwork in to register in Texas and in my County back home they do not do emissions testing so passing emissions isn't a big concern right now. I'll browse Ebay and see if I can find a factory gas cap.
 
There shouldn't be any pressure in the tank, regardless of elevation change.
My thought was that it was leaking out, but if you have pressure building, that's another issue.

Possibilities that I thought of/seen:
1) You have a vent problem/ hose routeing issue which is causing the tank not to vent.
2) Someone rerouted the hoses by accident and are pressurizing the tank.
3) And I saw this on JF. Some folks with abbreviated exhaust systems point have pointed the exhaust at the fuel tank, causing the tank to heat rapidly.

The vent hoses are not huge (1/8" or so). Vents are known to clog occasionally.

Also, FWIW: Please don't post how you intend to skirt laws, we really don't need or want to know :D
 
I'm not skirting anything. I'm stationed here and a Texas resident, so I can legally register the vehicle in Texas. Since I'm just "visiting" California and all that, I have no plans to stay here so I don't plan on keeping Cali tags on this thing.

I'll crawl under there tomorrow and check all my hoses and routing.
 
Last edited:
souske said:
Eliminating federal emissions equipment is a felony.

Please just fix it the right way, its really not that hard.
Click to expand...

Please tell me where in this thread I planned on eliminating emissions equipment? I did ask about a vented cap since I had no idea if one was supposed to be there or not.
 
Last edited:
devildog0 said:
I'm sending the paperwork in to register in Texas and in my County back home they do not do emissions testing so passing emissions isn't a big concern right now. I'll browse Ebay and see if I can find a factory gas cap.
Click to expand...

devildog0 said:
Please tell me where in this thread I planned on eliminating emissions equipment? I did ask about a vented cap since I had no idea if one was supposed to be there or not.
Click to expand...

By installing a vented cap, rather than fixing the issue, you would be effectively eliminating the evap system.

Glad to hear you are no longer considering this course of action
:cheers:
 
devildog0 said:
I'm not skirting anything. I'm stationed here and a Texas resident, so I can legally register the vehicle in Texas. Since I'm just "visiting" California and all that, I have no plans to stay here so I don't plan on keeping Cali tags on this thing.
Click to expand...
Same goes for the Great State of Colorado. :thumbup:

FWIW, my '90 (I know, apples and oranges) does build pressure in the fuel tank, especially when I go play in the mountains.

How full was the tank when fuel leaked past the cap?
 
WB9YZU said:
My thought was that it was leaking out
:D
Click to expand...

I'm not citing the CA laws necessarily...I really don't care if you bypass any system.

When I bought my 88 MJ the "rollover valves" were broken and one had actually dropped in to the tanks leaving about a 3'4" - 1" hole in the top of my tank. I had strong fuel smell when my tank was full-ish. When I dropped the tank to fix it there were streaks/stains on the top and side of the tank where gas had sloshed out and dribbled down the tank. The other valve was not far behind and also had some smaller slosh/leak marks. This could be a source of the gas smell.

Easy enough to at least check your valves and repair or replace if necessary. Then you wouldn't have fuel leaking out, let alone vapors. The vacuum lines when attached will suck out any pressure if that's indeed happening.
 
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