Excessive fuel tank pressure

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Alvin,

Let me recap:

vent line from Canister to fuel tank is clear.
new Canister
still checking to see if the vent line from the bottom of the canister to the frame rail is clean.

Well, that leaves the stupid gas cap. Tried switching it out with another vehicle to see if that helps?

Head scratcher this one :hhmm:
 
alia176 said:
Alvin,

Let me recap:

vent line from Canister to fuel tank is clear.
new Canister
still checking to see if the vent line from the bottom of the canister to the frame rail is clean.

Well, that leaves the stupid gas cap. Tried switching it out with another vehicle to see if that helps?

Head scratcher this one :hhmm:
Click to expand...


New OEM gas cap.



Gonna trouble shoot this in the morning. There has to be something blocked, kinked, clogged or broken. I don't buy the boiling gas thing. Otherwise this would be a massive problem in southern AZ every summer. It's a 15 year old rig, something needs cleaning or fixing.

Hopefully I'll find the problem and report back.
 
MaddBaggins said:
New OEM gas cap.



Gonna trouble shoot this in the morning. There has to be something blocked, kinked, clogged or broken. I don't buy the boiling gas thing. Otherwise this would be a massive problem in southern AZ every summer. It's a 15 year old rig, something needs cleaning or fixing.

Hopefully I'll find the problem and report back.
Click to expand...


when you do let JFZ80 know as he's killing tanks left and right.
 
My truck did fine up until I installed the OEM subtank, then it came down with the same issues you describe. I used everything factory except the main fuel filler hose to the subtank and I did not replace the lines on the transfer pump assy. I know for a fact the fuel filer hose has a very small air leak in it and that the transfer pump assembly also has a small air leak in one of the hoses. I am fairly certain that our heat and sudden elevation changes mixed with a small amount of air being allowed to escape does something to our pressurized gas tank systems. Let us know what you find Alvin.
 
Mine did the same today on the trail. But Im at almost sea level. Filled up this morning and had some overflow. Ran 90 miles down I-10 to trail in Milton,FL. Temps on the Scanguage never exceeded 200 (mostly 190-195). Got on the trail going thru some super steep, off camber etc spots and I notice gas smell. We stopped and when I pulled the TO TANK line off the charcoal canister under the hood I heard a boiling noise. Undid the gas cap and vented for about a minute. Put the cap on and let the truck run for a few minutes, pull the cap and it vented for a few more-did this twice.

Kept riding, checking everytime we stopped and over the afternoon it improved to the point that after driving home when I opened the cap it only vented for a few seconds like normal.

Im thinking it was a fluke and It's from possibly overfilling the tank or spilling gas into the vent line this morning. Now Im not so sure and wonder if I need to trouble shoot everything or just keep an eye on it. We are moving to Texas in a week and Ill be pulling a trailer with the truck so it needs to be ready. Im doing cooling flush this week.
 
OK Ross and I are working the problem.
Line to tank - clear
line from bottom of canister - clear
VCV - passed
check valve - passed
TVV cold engine check - passed
VSV and VCV hot engine check - passed
charcoal canister - failed..again so I have a problem somewhere and toasted another canister

after engine cools I'm gonna pull the TVV and bench test it. Then I guess I'll pull the VSV and bench test it also. After that I'm at a loss. I have a new fuel pump and pump filter, maybe I'll put those in for giggles.

Anybody...Dan...Robbie...
 
landtank said:
there is a line on the bottom of the charcoal canister that runs down to a nipple mounted to the frame. Check to make sure that the other end of that nipple is clear and open.
Click to expand...



Rick, I'm confused. The line from the bottom of the canister goes about 18" then just ends. It's clear. Ross's is the same as mine, no nipple to the frame. Are we talking about the same thing?
 
Alvin,

Is it that easy to toast a brand new CC? I thought all they had inside was a spring loaded ball/check valve dealie, how in the heck can that go bad? :hhmm:

Anyway, I found a Taco CC that was the same diam and using that in my 80. I don't have a long term usage report, particularly how the thing handles the main + aux tanks full of gas and wheeling but this maybe an alternative for you.

This is a pretty much a PnP. The top two nipples are backwards and one of the nipple from the Taco unit is tad shorter and skinnier.

Before anyone asks me about the year of Taco, I don't recall. It's been sitting on the shelf for a year or so. Sorry!

Some pics.

Ali
100_2332.webp
100_2336.webp
100_2335.webp
 
Not having much luck getting the VSV out. Can't get the philips screw out. I think I'm gonna have to pull everything out to do that. To big of a job for today, I have things to do.

This sucks because it basically makes me afraid to do anything other that daily drive until I fix this.

How bad would it be to let the tank to canister line just vent to atmosphere?
 
MaddBaggins said:
Rick, I'm confused. The line from the bottom of the canister goes about 18" then just ends. It's clear. Ross's is the same as mine, no nipple to the frame. Are we talking about the same thing?
Click to expand...

On the ones that I have seen that line on the bottom of the CC goes to a nipple that is mounted in the frame.

Maybe the 94s don't have it. I would think they would since I think air goes both ways and being left open it could suck in debris.

I'll check toyodiy.com

Not sure the link will work, outlet tube

part number: 77779-60010
 
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landtank said:
On the ones that I have seen that line on the bottom of the CC goes to a nipple that is mounted in the frame.

Maybe the 94s don't have it. I would think they would since I think air goes both ways and being left open it could suck in debris.

I'll check toyodiy.com

Not sure the link will work, outlet tube

part number: 77779-60010
Click to expand...

Thats interesting. Both Ross' and mine just end towards the back of the firewall. That line is clear. Your link shows a good pic of a nipple and bracket, but we don't have that at all.



OK, the return line from the fuel pressure regulator to the tank is clear also. Ross and I are both leaning toward VSV or possibly the TVV. I'm going to probably order both of them, test the new ones, remove the old ones and test them and then replace them both.

Is there any way the pressure regulator could be causing any problem?

I had a new fuel pump and sock and since we were screwing with the fuel system, we changed that out just because.
 
Here's what confuses me. The FSM test for the charcoal canister says to blow compressed air into the tank pipe and air should escape from the purge pipe and the bottom pipe without resistance. This part of the test my canister passed.

If this is true how could the tank build up pressure? Even if everything after the purge side was broken, the fuel vapor and pressure should just blow thru the canister and out the bottom. How can I be building up pressure then?
 
I don't have a charcoal canister. The return line is still there and still receives the waste vapor into the intake manifold for start up burn.

The other line I put a small filter on it and extended the soft line and it vents into the atmosphere.

Is this kosher? Probably not in any emissions jurisdiction that I know of...

I have some venting from the fuel cap on very hot days when I open up to fuel, but after about 6-8 seconds the venting from the gas cap stops.

Take it for what its worth Alvin. I'm not a fuel system expert (or any expert for that matter).

:)
 
MaddBaggins said:
I'm trying, it seems there is a number of people who have this issue.
Click to expand...

I had this occur to me the other day. Walked back past my fill port towards the back, and smelled gas strongly. It was not venting from the cap, but somewhere underneath. I opened the cap, and it vented for about 10 seconds, and has seemed fine since.

It only occured to me after a fill up where the guy had gotten it perhaps a bit too full, and it was relatively hot that day. :meh:
 
raydouble said:
What about heat from exhaust? Stock exhaust? Missing heat shields?
Click to expand...

Doesn't appear to be an issue. I have a stock exhaust. Alvin does not. I think there is a problem in the EVAP system. Alvin passed all the tests laid out in the FSM for a running truck. We bench tested the VCV and check valve. We need to bench test the VSV and another valve that is opened when the truck warms up.

Does anyone have a ballpark price on the VSV or TVV parts? I hate the idea of throwing parts at the problem yet getting to those parts is a bit of a PITA without tearing down alot of the air intake. For that matter the air intake maybe a bit dirty allowing pressure to build up.


One question I have is with the fuel pressure regulator. What symptoms would there be if it wasn't behaving. Sort of a long shot hail Mary kind of speculation.
 
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