Vacuum in the fuel tank

[rion]

guys, what is the best way to relieve fuel tank pressure? the pressure is great that the cap cannot be remove if you close the cap tight. even when not tight, when I remove the fuel tank breather pipe, I will hear vacuum.

Both ends of the breather hose seems NOT blocked. because when I tried to blow air to it. I hear air passing either ways in or out.

I already switch the cap from another same ride, but same problem. the other ride seems working fine with the suspected cap.

any solutions?

I read that one solution is to drill hole in the cap. but is it really safe? a fuel singaw from the fuel cap hole seems dangerous.

[fourtheboys96]

i think your talking about fuel pressure and not vacuum. if that is the case, you don't need to worry because its normal. gasoline is a volatile substance and tends to evaporate resulting to build up of pressure inside the tank.

if i am not mistaken, this pressure helps deliver fuel to the engine.

[rion]

it's vacuum, its giving me hard time opening the fuel cap once closed shut.

[bambino]

what's the year model you have?

most OBDII SYSTEMS are equipped with computerized EVAP SYSTEMS and that can only be corrected by using a scanner to properly diagnose it with the aid of smoke machine.

[rion]

it's old 95'. and it doesn't have OBDII slot unfortunately.

[v6dreamer]

The breather system is probably plugged. There is a tube from the gas tank to the evap emission canister to control the emmission of VOC (fuel fumes), the canister absorbs the fumes, hydrocarbon and sends liquid gas back to the tank. Check for any plug lines. It also vents excess pressure with greatly reduced VOCs. Somewhere along the line, some thing is blocked.

Warning - the old canister is highly flammable.....so be very careful.

[rion]

I didn't see or maybe didn't notice a canister. but Both ends of the breather hose seems not blocked. because when I tried to blow air to both ends. I can hear good air flow either ways in or out.

illustrated in this wonderful drawing. "blowed" are colored blue.


10kb

but will do try to look again if there is a canister hidden somewhere. thanks.

[v6dreamer]

Open hood, usually (sorry dont know what kind of car and model of your car) it will be on the right side of the car (passenger) and at the front in the area to the right side of the radiator. It is an oblong shaped box that has a round cap on it.

To easily identify this, the black round cap on it has 2 lines coming to it, one is the vacuum line and the other is the bleed line. This box is fairly easy to see naka-bolt sa tabi. Palitan mo na baka sira na, check also your "evap bypass soleniod valve" and the "vent control valve" are located under the vehicle, roughly below the left rear seat area. They short out due to corrosion/contamination from water seeping into the valves.

[rion]

no evap emission canister unfortunately, it's a toyota 2.0LT diesel.

[bambino]

ipagawa mo agad sa shop yan baka sumabog pa sa iyo yan .

compressed air + diesel = ignition

[yapoy86]

as per rion illustration.. its not the breather hose but rather the overflow hose.. over flow hose is connected in the tank upper portion going near the fuel filler cap.. its there to flush the air while the tank is being filled with fuel (two matters cannot occupy the same space) ... breather is another thing.. As far as i know.. diesel tanks doesnt have that canister since diesel is not that volatile compared to gasoline.. diesel tanks use breathers with a one way valve where the air can be taken IN but will let fuel fumes pass out very slow just to relieve pressure..

you need to find the breather usually a small hose.. and trace the valve and clean it.. do not put a hole in your cap as this may spill your fuel when the vehicle pass thru bumps and holes

[v6dreamer]

no evap emission canister unfortunately, it's a toyota 2.0LT diesel.

Diesel ba! Kala ko gasolina.

Pero tama si bambino.......you are a running TIME BOMB.

[Dieseldude]

Diesel tanks have breathers which can be located anywhere in the tank, including the tank's filler cap. As the fuel pump draws fuel from the tank; the breather allows atmospheric pressure into the tank.


A blocked breather will put the fuel tank on high negative pressure (vacuum), resulting in the following:

1. low power
2. hard start condition
3. an imploded fuel tank.

[rion]

thanks guys, will try to look deeper. baka nandun lang yang breather sa tank.

wala bang breather filler cap available sa market natin? incase wala akong makita sa ilalim...

medyo takot talaga ako sa drilling a small hole sa cap. it vacuums when running and blows fumes when shaken...

[mbeige]

If you're a bit worried, the fuel sender unit for the fuel gauge should be located on top of the fuel tank and in theory could be used as a way to bypass the bad vent system, assuming it is a bad vent system. I'm thinking since if it's on top of the fuel tank there's very light risk of fuel spilling. Just don't go with a full tank.

[rion]

I think I found the real breather, I'm not sure just yet, because I can't see it clearly and reach it.

I do not worry much about fuel spill, but the vapour. I found a vid on youtube about 20ml of meth vapor that could cause this.

20 ml of methanol is injected into a 5 gallon water cooler jug and allowed to turn to vapor

[rion]

I was able to reach the breather today... and was able to fix it ACCIDENTALLY...

finaly confirmed that it was breather and was able to reach and remove it. tried blow and suck it each end and it was blocked indeed.

so I wash it up with soap and water so I can take a pic and return it to it's place. use the pic when looking for replacement.



before I returned it, I made sure there was no water inside, so I smash it gently to the chair to shake and purge the water out. but when I tried blow and suck it this time, the breather is now working one way route. air only comes in but can't get out. lovely, it is fixed now. hopefuly hindi bumigay.

thanks a lot guys. appreciate the help. * yapoy86: thanks for the tip.