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Fuel tank always feels pressured?


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okay so i drive a 280zx with a 2jz single turbo, prior to that PO had an rb20 installed.. anyways when I bought it with the rb20 engine, I drove for as little as 5 miles, and I would park, turn the car off, open the fuel tank lid, it had sooo much pressure leaving the fuel tank..

 

when the rb20 died, I got a 2jz, installed bosch inline fuel pump (thinking it might fix the problem) but still whenever I drive 5 miles or even 100 miles, and I open the fuel tank, soo much pressure leaves (it once burned my skin cause the pressure was too strong even if i slowly open it  :icon53:  )

 

anyways, I was wondering does anyone have this sort of problem? because I did search a few times but honestly found nothing..

 

Thanks  

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The factory system has a vented fuel tank.  Sounds like yours are clogged or someone blocked them off.  Maybe to get rid of "emissions crap".  Check your vents.  There's a nice diagram out there somewhere of all of the various hoses and valves.

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You car originally vented the fuel tank to a charcoal canister. Most likely an ignorant previous owner removed "all the emission crap" as mentioned above. A pressurized fuel tank is dangerous. Fix the venting system on your tank.

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I will be the third voice of reason here--the charcoal cannister on the inner side of the front right wing has a cap on it, that cap regulated how much pressure built up in the tank due to expansion. After a given point, it released it to the container, which then flowed the releasing gas through the activated charcoal bed and to atmosphere. This adsorbed the fuel vapors.

 

The important thing here is this: If the vent was plugged, there is little chance the fuel expansion due to heat would overcome the fuel sucked out of the tank in that time and cause a net pressure rise. Generally if you plug the vent, at highway speeds you will see in about two hours problems with fuel pressure being low...and a VACUUM in the tank, as opposed to pressure.

 

In short drives, I can see this being an issue. In long term drives, especially at high speeds it should draw down the tank if it's indeed plugged.

 

You need to quantify the pressure there---it should be inches of water, and the volume can be quite great. A compound mm H2O gauge (reads pressure and vacuum) on the Evaporative Emissions Line from the cannister to your tank should read the working pressure of the tank. Sitting idling it will rise to a set point, and then relieve to the cannister. If that valve is sticking it will cause that pressure. It's a separate flapper that breaks the vacuum to your tank...and like I said, I can't explain pressure in the tank after 100 miles of high speed driving, every one I've been in with a plugged line pulled heavy vacuum in about 2 hours-so much so it stranded the guy on the roadside.

 

That gauge may be your only hope of diagnosis. What you think is 'excessive' may indeed be normal. If you have 120mm H2O with a full tank it will give a short "psssh"... but that same pressure at an almost empty tank will blow for much longer. Chances are you have a sticking relief valve but not a plugged / capped line.

 

Let us know what you find! 

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The factory system has a vented fuel tank.  Sounds like yours are clogged or someone blocked them off.  Maybe to get rid of "emissions crap".  Check your vents.  There's a nice diagram out there somewhere of all of the various hoses and valves.

 

I will try and check if its clogged this weekend.

 

 

 

You car originally vented the fuel tank to a charcoal canister. Most likely an ignorant previous owner removed "all the emission crap" as mentioned above. A pressurized fuel tank is dangerous. Fix the venting system on your tank.

Well.. the previous owner was a real ass towards the car.. I'm spending soo much time trying to fix it on my own as much as I can, and i'm learning as im going.  Yeah I'm always scared it might build up soo much pressure that it might blow up :(

 

I will be the third voice of reason here--the charcoal cannister on the inner side of the front right wing has a cap on it, that cap regulated how much pressure built up in the tank due to expansion. After a given point, it released it to the container, which then flowed the releasing gas through the activated charcoal bed and to atmosphere. This adsorbed the fuel vapors.

 

The important thing here is this: If the vent was plugged, there is little chance the fuel expansion due to heat would overcome the fuel sucked out of the tank in that time and cause a net pressure rise. Generally if you plug the vent, at highway speeds you will see in about two hours problems with fuel pressure being low...and a VACUUM in the tank, as opposed to pressure.

 

In short drives, I can see this being an issue. In long term drives, especially at high speeds it should draw down the tank if it's indeed plugged.

 

You need to quantify the pressure there---it should be inches of water, and the volume can be quite great. A compound mm H2O gauge (reads pressure and vacuum) on the Evaporative Emissions Line from the cannister to your tank should read the working pressure of the tank. Sitting idling it will rise to a set point, and then relieve to the cannister. If that valve is sticking it will cause that pressure. It's a separate flapper that breaks the vacuum to your tank...and like I said, I can't explain pressure in the tank after 100 miles of high speed driving, every one I've been in with a plugged line pulled heavy vacuum in about 2 hours-so much so it stranded the guy on the roadside.

 

That gauge may be your only hope of diagnosis. What you think is 'excessive' may indeed be normal. If you have 120mm H2O with a full tank it will give a short "psssh"... but that same pressure at an almost empty tank will blow for much longer. Chances are you have a sticking relief valve but not a plugged / capped line.

 

Let us know what you find! 

 

Thank you for the extensive reply, my stock fuel gauge just died.. and I think maybe thats why I keep having fuel cutting issues? but I will try my best to get around this issue, I hope this will sort out the fuel cutting issue as well.. 

 

Thanks for the replies guys I appreciate it. 

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At low speeds and depending on the pump, a lot of fuel can be returned to the tank.  In addition, fuel temperature rise can cause tank pressurization.  In extreme cases, like an exhaust system falling off, bending the vent line shut, and the exhaust blowing directly on a metal tank - the tank pressure can increase so much that the tank balloons and tears the straps off the car.  Don't ask me how I know that and thank God for Toyota quality.

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At low speeds and depending on the pump, a lot of fuel can be returned to the tank.  In addition, fuel temperature rise can cause tank pressurization.  In extreme cases, like an exhaust system falling off, bending the vent line shut, and the exhaust blowing directly on a metal tank - the tank pressure can increase so much that the tank balloons and tears the straps off the car.  Don't ask me how I know that and thank God for Toyota quality.

 

well.. today I was studying about pumps and stuff like that.. and I had a "breakthrough" idea .. I decided to drive the car without the fuel tank cap.. the fuel cutting problem got solved... the car sounds different as if it was breathing better  :mellow: and it actually feels a lot stronger than before ... so i think for now i'm gonna see if I can find a fuel cap. (i'm hoping I don't run into this problem again.. and i'm hoping its the fuel cap that was the whole cause of it )

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The cap only lets air in, through a spring-loaded valve.  Not out.  There's no easy solution.  Unless you confused air escaping with air entering.  Air entering wouldn't cause a "burn" though.  Find the charcoal canister, or the lines to it, and make them work.

 

 

p.s. Use more capital letters.

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The cap only lets air in, through a spring-loaded valve.  Not out.  There's no easy solution.  Unless you confused air escaping with air entering.  Air entering wouldn't cause a "burn" though.  Find the charcoal canister, or the lines to it, and make them work.

 

 

p.s. Use more capital letters.

 

 

Well english isn't my first language :P , yeah I might've mixed them up, but if it is working fine for now I'll keep it like that, till I can get around it and check the charcoal canister.

 

Thanks :D

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Crawl underneath the rear of the car. The fuel sender/supply assy sits on the top of the tank. If you look on the front of the tank you should see three lines coming from it. One line is the inlet to the pump. One is the return to the tank. The smaller line of the three is the vent that should have gone to the charcoal canister (this is on a US market car at least, so your car may be different).  Follow that line towards the front of the car and see where it has been capped or blocked. Chances are the previous owner didn't cap it by the tank, but in the engine bay somewhere.

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