Excessive fuel tank pressure

This site may earn a commission from merchant affiliate
links, including eBay, Amazon, Skimlinks, and others.

I believe a number of people who have this issue (including myself) have aux tanks. Is this happening to people who don't have aux tanks?

The only time it happened to me I was heading off to Death Valley and fueled up about 15 miles before getting on the trail. I filled the tank and sub tank as full as I could. It seems that was a mistake - that overfilling can cause problems. So, has anyone confirmed if this pressure problem occurs when the tank not full? I don't know if it's relevant, but it would be useful to try to determine similarities between everyone's trucks/situations.
 
Just for a little bit of reference Ebag333 and I live in the same city, climate, etc. I have not experienced any of this. We typically wheel together as well. I own a 94 pretty much stock and min. PM at this point. FWIW HTH.
 
Alvin/Ross,

My 94 still does this even after replacing the VSV & TVV, which I did two months ago when I rebuilt my engine.

Strangely, the tank even built up pressure without the engine in. I noticed the smell of gas one day and noticed it was peeing out of the fuel line that would normally connect to the fuel filter. I clamped the line and periodically cracked the cap to vent the tank on the warmer days when the a/c was not on out in the shop.

I mainly purchase gas from QT up here in the valley. Not sure of they have additives that lower the boiling point of the gas that cause it to boil off sooner than another brand of gas. Since all of the fuel up here comes from the tank farm out in west Phoenix, it's hard to say which brand(s) might have different additives. I also fill up our Corolla at QT but don't have the same issues, and it sits out in the sun all day.:meh:
 
gotmud said:
Alvin/Ross,

My 94 still does this even after replacing the VSV & TVV, which I did two months ago when I rebuilt my engine.

Strangely, the tank even built up pressure without the engine in. I noticed the smell of gas one day and noticed it was peeing out of the fuel line that would normally connect to the fuel filter. I clamped the line and periodically cracked the cap to vent the tank on the warmer days when the a/c was not on out in the shop.

I mainly purchase gas from QT up here in the valley. Not sure of they have additives that lower the boiling point of the gas that cause it to boil off sooner than another brand of gas. Since all of the fuel up here comes from the tank farm out in west Phoenix, it's hard to say which brand(s) might have different additives. I also fill up our Corolla at QT but don't have the same issues, and it sits out in the sun all day.:meh:
Click to expand...


Alvin and I are completely confused. We are going to try and pressurize his tank and see what happens. The tank breather line is clear from the charcoal canister to the tank. Pressurizing will show that it is clear the other way. I don't see a valve of any sort on this tank breather.

Alvin's TVV and the VSV controlling this system checked out during running checks as well as bench testing the other valves.

I don't know enough about the system but to throw out WAGs. Could the fuel pump be pushing too much fuel to the filter (relay or other control mechanism) and causing too much warm/hot fuel to return to the tank via the fuel pressure regulator and tank return line? This could pressurize the tank during warm temps and rapid changes in altitude. The excess fuel vapor could then overwhelm the charocoal cannister causing premature failure. :confused:
 
IIRC, there is a check valve somewhere between the cc and the gas tank. I have yet to look for it, but I just might later this evening. I suppose it is possible this valve could be bad and is letting too much pressure return to the tank. Once again...:meh::confused:
 
on a trail run this summer we had a guy with a 91 boil off 5 gallons of fuel. The first thing he noticed was a hissing sound coming from the CC. When he pulled the gas cap the tank vented for something like 10 minutes and you could hear the gas boiling.

If everything checks out I'm thinking the evap system is getting overwhelmed from pressure do to expanding gas and just can't vent it fast enough. With more and more people having this problem it might be a good idea to change out all the soft lines. They might be swelling with age adding some restriction.

Just a wild ass guess but from where I'm sitting it would be my next move.
 
Just another cruiser with the same problem. Always just had a few seconds at fillup, but on recent trip from AZ to WY, it vented for several minutes. Was fine on the next fillup. Interested to see if it was an isolated event or happens in the near future. Subscribed with interest.:hhmm:
 
It sounds like the charcoal inside the canister has expired on our older rigs. FirstToy replaced his charcoal and all has been well ever since. If these things weren't so expensive, more and more of them would be replaced I'd imagine.
 
I had this happen to me going up and through Denver. The way I solved it was I bought a second gas cap and drilled a small hole in it. In essence making it a vented cap. I may have made a check valve with a ball for it. It was 7-8 years ago and I can't remember. The original cap is good for emissions if there is testing.

Bill
 
alia176 said:
It sounds like the charcoal inside the canister has expired on our older rigs. FirstToy replaced his charcoal and all has been well ever since. If these things weren't so expensive, more and more of them would be replaced I'd imagine.
Click to expand...

My cc is brand new. Changing it made no difference at all.
 
I talked to CDan yesterday and learned that the charcoal canister of the 93/94 model years is now discontinued. 95-97 is a different part number. No clue if there is a difference but since my canister failed spectacularly in the FSM test, I am taking a chance this will work fine as a replacement. I ordered a new gas cap with thoughts of creating a vented gas cap.

One thing I am not sure of is the breather hose coming out of the tank. There is a part called something along the lines of some sort of valve. I guess I could see a way where this is a one way valve to the canister that can get gummed up if the tank gets overfilled which also hurts the charcoal canister.

IIRC people with sub tanks fill the main tank through this line. Can anyone recall if there is some sort of one way valve there.
 
I wonder if fuel mix has changed to lower the vapor pressure enough to overpower the system? I know that some additives were not run here in the summer because of this, maybe this has changed or they are getting close to the line?

I haven't noticed this problem, but when we were on 4 Peaks a couple of weeks ago (~4000ft climb), noted that all of the rigs there had gas smell.

This maybe helpful?
http://www.autoshop101.com/forms/h62.pdf
 
alia176 said:
It sounds like the charcoal inside the canister has expired on our older rigs. FirstToy replaced his charcoal and all has been well ever since. If these things weren't so expensive, more and more of them would be replaced I'd imagine.
Click to expand...

Ali, that would be a thought, but I replaced mine last summer when this problem first arose. problem is still there.

I think I will make a vented cap or pull the line to the cc when I do any elevation and just let it vent to atmosphere.

I think Tools may be on to something. That gas smell is the first indicator Kevin.
 
Maybe I should stop hitting the cheap station and fill up with Chevron during the summer and see what happens. It would be a cheap experiment.
 
My limited research points to this as an issue, especially in the spring when the blends switch.

Something is overwhelming the HVAC system which I guess leads to premature charcoal canister failure. Too much hot gas returning to the tank after the fuel pressure regulator? Intermitent failure in any of the three valves that purge vapor from the canister to the intake? Patially blocked tank breather line from the tank to the canister?

FJ40Jim advises to just swap the purge and tank lines on the canister to bypass the HVAC system in a 60. Maybe it would help an 80 in
duress?

I read that PDF you posted. It advises not using shop air to pressure test parts of the system. Something about oxygen and gas and explosion. Alvin and I are/were planning on trying to pressurize his tank at the filler to check if that breather hose is. Should be intersting. :grinpimp:

Tools R Us said:
I wonder if fuel mix has changed to lower the vapor pressure enough to overpower the system? I know that some additives were not run here in the summer because of this, maybe this has changed or they are getting close to the line?

I haven't noticed this problem, but when we were on 4 Peaks a couple of weeks ago (~4000ft climb), noted that all of the rigs there had gas smell.

This maybe helpful?
http://www.autoshop101.com/forms/h62.pdf
Click to expand...
 
to throw another ":flipoff2:what if" in the mix;

are you just recently seeing E10 in your area?

WAG here but I speculate the petro-chem industry is stretching the fuel out to the ragged end and it is not doing well with our somewhat older rigs? :meh:
 
Have you tried switching grades? I'v got a truck that cannot tolerate 87 in the summer because of the volatility, but runs fine with it in the winter.:meh:
 
splitshot said:
Have you tried switching grades? I'v got a truck that cannot tolerate 87 in the summer because of the volatility, but runs fine with it in the winter.:meh:
Click to expand...

With the mileage this thing gets and the price of gas, I hadn't considered that.
 
I didn't either till I read through this thread, worth a try...

That does mean another high altitude run in the near furture.;)
 
You must log in or register to reply here.

Share this page

Back
Top Bottom