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Topic: Pressure building up inside gas tank, bad? (Read 1460 times) previous topic - next topic

Pressure building up inside gas tank, bad?

About a couple months ago I upgraded my fuel pump to a 255 walbro from jds
Idk if it really happened before then but I've noticed that pretty much everytime I go to put gas in my tank there is a ton of pressure in my gas tank
If I just unscrew the gas cap a little and let it hiss out it is completely done after about 15-25 seconds but I usually just take the gas cap all the way off and let it gush out

Is this bad or should I just leave it?
My car is running tip top currently with about 197,xxx on the clock, just wondering if it happens to anybody else
1987 T-Bird TC: 5-Spd, 5-lug conv., CHE Rear CAs, '04 Cobra wheels and 13" Brakes, Vac Assist conv: '93 Cobra BB/MC & Wilwood PV, Gutted/Knived Intakes, T3 turbo, RFE6 Mani, Stinger 3" Exhaust & Oil Feed, 255HP Walbro, Kirban AFPR, RR Cam, Esslinger Cam gear and Round Tooth Conv., Gillis Boost Valve, Speedway Dual Valve Spring,  K&N, 130a 3g Alt conv., 140mph Speedo
Running Better Than Ever :burnout:

Pressure building up inside gas tank, bad?

Reply #1 –
Sounds like the evap line might have got crushed during the install

Pressure building up inside gas tank, bad?

Reply #2 –
Where are these evap lines usually located?
1987 T-Bird TC: 5-Spd, 5-lug conv., CHE Rear CAs, '04 Cobra wheels and 13" Brakes, Vac Assist conv: '93 Cobra BB/MC & Wilwood PV, Gutted/Knived Intakes, T3 turbo, RFE6 Mani, Stinger 3" Exhaust & Oil Feed, 255HP Walbro, Kirban AFPR, RR Cam, Esslinger Cam gear and Round Tooth Conv., Gillis Boost Valve, Speedway Dual Valve Spring,  K&N, 130a 3g Alt conv., 140mph Speedo
Running Better Than Ever :burnout:

Pressure building up inside gas tank, bad?

Reply #3 –
It's not venting. Check that the carbon canister isn't plugged up then go after the lines like was suggested. The canister is easy to check before you go through dropping the tank back down to get to the lines. Chances are that's what you'll be doing.

Pull the line off the canister that leads back to the tank and see if your problem goes away. There is a check valve on the tank, so blowing back won't tell you anything, unfortunately. If you have a vacuum tool you can hook it to the line to see if you can get free air flow from the tank. If it draws a vacuum with the fuel cap off the line is crushed.

Pressure building up inside gas tank, bad?

Reply #4 –
i have to chase down this issue on my 20th as well,, for now i leave the cap a tad bit loose.

Pressure building up inside gas tank, bad?

Reply #5 –
Question...

If the tank can't vent and fuel pump is pumping fuel out of the tank, how can it build up pressure??? Removing fuel will create a vacuum and possibly collapse tank(that I have witnessed with mechanical pumps)... I can see pressure building with high fuel level and high ambient temp but again as fuel level drops so would pressure...

Sooo I'm askin', are you guys sure it's pressure and not vacuum???

Pressure building up inside gas tank, bad?

Reply #6 –
I've only had a pressure problem once and that's because I was running open lers and it was heating the tank lol

Pressure building up inside gas tank, bad?

Reply #7 –
It's definitely pressure
I can feel the gas vapors blow by my hand as I unscrew the gas cap
I don't recall coming into contact with any lines that could have been crushed when I replaced my fuel pump so I don't know

I also wanted to note that I am running a k&n air filter so any tubes from the stock air box that were connected to the carbon canister are now not attached
1987 T-Bird TC: 5-Spd, 5-lug conv., CHE Rear CAs, '04 Cobra wheels and 13" Brakes, Vac Assist conv: '93 Cobra BB/MC & Wilwood PV, Gutted/Knived Intakes, T3 turbo, RFE6 Mani, Stinger 3" Exhaust & Oil Feed, 255HP Walbro, Kirban AFPR, RR Cam, Esslinger Cam gear and Round Tooth Conv., Gillis Boost Valve, Speedway Dual Valve Spring,  K&N, 130a 3g Alt conv., 140mph Speedo
Running Better Than Ever :burnout: