Pressure In Fuel Tank

[blackpoolbobbie@btinternet.com]

hi i have a 92 previa auto ive noticed when im filling up there is a lot of pressure when i undo the petrol cap can anyone help please

[Boro Sera]

as far as I know there are 2 things to prevent this.

1. There should be a breather pipe on the petrol tank that exits under the car somewhere.

OR

2. the petrol cap itself should have breathing capabilities.

Both of these solutions can become blocked with general gunk over time. Especially the pipe method though, as this usually exits the car just behind a rear wheel.

Sorry I can't be more specific.

Rich

[blackpoolbobbie@btinternet.com]

as far as I know there are 2 things to prevent this.

1. There should be a breather pipe on the petrol tank that exits under the car somewhere.

OR

2. the petrol cap itself should have breathing capabilities.

Both of these solutions can become blocked with general gunk over time. Especially the pipe method though, as this usually exits the car just behind a rear wheel.

Sorry I can't be more specific.

Rich

←

thanks anyway mate

[miti-babe]

Bobbie

The Previa has two venting systems... the most obvious is the fuel cap, which only appears to vent down to a certain residual pressure - probably because it has a pressure releif valve built in to vent after that pressure is reached...

The not so obvious one is the Evaporative Emissions Control System (called EVAP by Toyota)...

The fule tank on the Previa has a top like a double-humped camel... at the top pf each hump is a vent... these vents are connected together and lead forward to a charcoal cannister with a 3-way ball valve in the top... :bookworm:

The first way is the connection to the tank vents...

The second way is a connection to the inlet manifold via a small brass pipe on the throttle body...

The third way is a drain, which exits the top of the cannister and leads, via qute a large pipe to the front suspension cross-member, where is passes through a grommet and into the member...

When running normally, the vents pass fuel vapour into the charcoal and this is recirculated into the engine via the throttle body...

When broken, the charcoal cannister fills up with fuel and overflows into the cross-member, where it then pees out all over the floor... :o

My '91 model was doing this when I bought it... I couldn't find out why and my Toyota mechanic suggested that only replacing the cannister (nearly £200) would rule out a fault there... I removed the cannister and blocked off the various pipes... problem gone, but the tank now only vents via the cap and if this is released immediately after driving (like when refuelling) there is a substantial amount of pressure (not massive, but a clearly audible hiss...) This dissipates overnight, so I'm reassured that an explosion is not imminent...

So. my advice is to check under the N/S sill, just in front of the fuel tank and next to the fuel filter... if the cannister is there, check that it's connections are still made... if it's missing, there will probably be a 8mm i/d fuel pipe with a bolt stuffed into it or some other sort of cap..

If it all seems OK, the cannister may well be blocked (they are regarded as "consumables") and will need replacement... (got a spare £200?) B)

Good Luck

Jeff

[blackpoolbobbie@btinternet.com]

Bobbie

The Previa has two venting systems... the most obvious is the fuel cap, which only appears to vent down to a certain residual pressure - probably because it has a pressure releif valve built in to vent after that pressure is reached...

The not so obvious one is the Evaporative Emissions Control System (called EVAP by Toyota)...

The fule tank on the Previa has a top like a double-humped camel... at the top pf each hump is a vent... these vents are connected together and lead forward to a charcoal cannister with a 3-way ball valve in the top... :bookworm:

The first way is the connection to the tank vents...

The second way is a connection to the inlet manifold via a small brass pipe on the throttle body...

The third way is a drain, which exits the top of the cannister and leads, via qute a large pipe to the front suspension cross-member, where is passes through a grommet and into the member...

When running normally, the vents pass fuel vapour into the charcoal and this is recirculated into the engine via the throttle body...

When broken, the charcoal cannister fills up with fuel and overflows into the cross-member, where it then pees out all over the floor... :o

My '91 model was doing this when I bought it... I couldn't find out why and my Toyota mechanic suggested that only replacing the cannister (nearly £200) would rule out a fault there...  I removed the cannister and blocked off the various pipes... problem gone, but the tank now only vents via the cap and if this is released immediately after driving (like when refuelling) there is a substantial amount of pressure (not massive, but a clearly audible hiss...)  This dissipates overnight, so I'm reassured that an explosion is not imminent...

So.  my advice is to check under the N/S sill, just in front of the fuel tank and next to the fuel filter... if the cannister is there, check that it's connections are still made... if it's missing, there will probably be a 8mm i/d fuel pipe with a bolt stuffed into it or some other sort of cap..

If it all seems OK, the cannister may well be blocked (they are regarded as "consumables") and will need replacement... (got a spare £200?) B)

Good Luck

Jeff

←

[blackpoolbobbie@btinternet.com]

Bobbie

The Previa has two venting systems... the most obvious is the fuel cap, which only appears to vent down to a certain residual pressure - probably because it has a pressure releif valve built in to vent after that pressure is reached...

The not so obvious one is the Evaporative Emissions Control System (called EVAP by Toyota)...

The fule tank on the Previa has a top like a double-humped camel... at the top pf each hump is a vent... these vents are connected together and lead forward to a charcoal cannister with a 3-way ball valve in the top... :bookworm:

The first way is the connection to the tank vents...

The second way is a connection to the inlet manifold via a small brass pipe on the throttle body...

The third way is a drain, which exits the top of the cannister and leads, via qute a large pipe to the front suspension cross-member, where is passes through a grommet and into the member...

When running normally, the vents pass fuel vapour into the charcoal and this is recirculated into the engine via the throttle body...

When broken, the charcoal cannister fills up with fuel and overflows into the cross-member, where it then pees out all over the floor... :o

My '91 model was doing this when I bought it... I couldn't find out why and my Toyota mechanic suggested that only replacing the cannister (nearly £200) would rule out a fault there... I removed the cannister and blocked off the various pipes... problem gone, but the tank now only vents via the cap and if this is released immediately after driving (like when refuelling) there is a substantial amount of pressure (not massive, but a clearly audible hiss...) This dissipates overnight, so I'm reassured that an explosion is not imminent...

So. my advice is to check under the N/S sill, just in front of the fuel tank and next to the fuel filter... if the cannister is there, check that it's connections are still made... if it's missing, there will probably be a 8mm i/d fuel pipe with a bolt stuffed into it or some other sort of cap..

If it all seems OK, the cannister may well be blocked (they are regarded as "consumables") and will need replacement... (got a spare £200?) B)

Good Luck

Jeff

←

thanks very much for that ill go have a look now and see if the cannister is there thanks

[blackpoolbobbie@btinternet.com]

:) thanks very much for that being a fellow glaswegian im really gratefull for that and no i dont want to pay £200 they are dear enough to run as is fuel consumption not very good so will have to put up with it thanks

Bobbie

The Previa has two venting systems... the most obvious is the fuel cap, which only appears to vent down to a certain residual pressure - probably because it has a pressure releif valve built in to vent after that pressure is reached...

The not so obvious one is the Evaporative Emissions Control System (called EVAP by Toyota)...

The fule tank on the Previa has a top like a double-humped camel... at the top pf each hump is a vent... these vents are connected together and lead forward to a charcoal cannister with a 3-way ball valve in the top... :bookworm:

The first way is the connection to the tank vents...

The second way is a connection to the inlet manifold via a small brass pipe on the throttle body...

The third way is a drain, which exits the top of the cannister and leads, via qute a large pipe to the front suspension cross-member, where is passes through a grommet and into the member...

When running normally, the vents pass fuel vapour into the charcoal and this is recirculated into the engine via the throttle body...

When broken, the charcoal cannister fills up with fuel and overflows into the cross-member, where it then pees out all over the floor... :o

My '91 model was doing this when I bought it... I couldn't find out why and my Toyota mechanic suggested that only replacing the cannister (nearly £200) would rule out a fault there...  I removed the cannister and blocked off the various pipes... problem gone, but the tank now only vents via the cap and if this is released immediately after driving (like when refuelling) there is a substantial amount of pressure (not massive, but a clearly audible hiss...)  This dissipates overnight, so I'm reassured that an explosion is not imminent...

So.  my advice is to check under the N/S sill, just in front of the fuel tank and next to the fuel filter... if the cannister is there, check that it's connections are still made... if it's missing, there will probably be a 8mm i/d fuel pipe with a bolt stuffed into it or some other sort of cap..

If it all seems OK, the cannister may well be blocked (they are regarded as "consumables") and will need replacement... (got a spare £200?) B)

Good Luck

Jeff

←