cygnusx1 Posted September 14, 2005 Share Posted September 14, 2005 Now that gas prices are sky high, I run the tank down lower than usual in my Z. (It's just a mental thing). I noticed that when I open the gas cap with the tank very low, I get a huge surge of relieving pressure rushing out of the filler neck. That isn't normal is it? I have stock 76 280Z fuel lines and tank. The vent line that use to go to the carbon cannister is open in the engine bay with a "little foam filter" over it. What gives? Quote Link to comment Share on other sites More sharing options...
TheNeedForZ Posted September 15, 2005 Share Posted September 15, 2005 what kind of foam filter? You might have plugged it. Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted September 15, 2005 Author Share Posted September 15, 2005 It's an air filter for a 2 Stroke RC motor. It is not clogged. So I take it that there should NOT be pressure built up in the tank? The vent line runs open from the front of the car right back to the tank or does it not? I wasn't sure if it was normal or not, this is the only Z I've had and it has been doing this for quite a while. Quote Link to comment Share on other sites More sharing options...
Z-Monster Posted September 27, 2005 Share Posted September 27, 2005 i also have had this problem as i take my z into the track once in awhile. it has not reoccured since i installed a fuel pressure regulator and replaced all my hoses running to and from the fuel tank. also checking the fuel tank breather helps. hope you get to resolve your problem as i did. Quote Link to comment Share on other sites More sharing options...
savageskaterkid Posted September 28, 2005 Share Posted September 28, 2005 My ZX did that, i didn't think much of it, i thought it had to do with pressure building up in the fuel lines so it could push the gas threw the lines easier. Quote Link to comment Share on other sites More sharing options...
bjhines Posted November 10, 2005 Share Posted November 10, 2005 OK..... Klick and Klack would have this one right off.... The Pressure you talk about is no higher than when the tank is full....If you doubt me then put a gauge on the vent lines..... The effect you are witnessing is called VAPOR PRESSURE.....In other words... gasoline WANTS to evaporate...it will evaporate until a certain pressure at whatever temperature prevents further evaporation.......Keep following me here..... What is happening is that an empty tnak has a great deal more available volume to fill up with a compressable mixture of gasses...(air and fuel vapor)... When you release the cap you are allowing this volume of gasses to decompress.... the empty tank vents a significantly larger AMOUNT!!! of air...but the pressure is no higher. Quote Link to comment Share on other sites More sharing options...
bjhines Posted November 10, 2005 Share Posted November 10, 2005 as far as your "vent line" being open to air.......Well..... you should deduce that from your initial question....It is OBVIOUSLY!!!!!! NOT!!!! open to atmosphere....clogged or not....your logic fails you if you think it is indeed venting your tank....keep in mind that tank vents are designed to let air INTO the tank NOT OUT of the tank. Ohhh... and another thing...if you are really concerned about gas prices....then you really dont want the vent line open to atmosphere.....your gasoline will "vent" (evaporate) from your tank at a rate proportional to the surface area of fuel exposed in the tank.... this is why we have those carbon canisters and check/flow valves. Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted November 27, 2005 Author Share Posted November 27, 2005 I completely understand vapor pressure is vapor pressure. That value changes with temperature. The volume of vapor that rushes out of the cap is a function of the volume of vapor in the tank. Now, I have never had the tank out of the car so I have no idea how many inlet or outlet ports there are on the tank. I do know that if I am building pressure in the tank, there are no paths that lead to atmosphere. Is that a function of a valve somewhere, a check valve, a clogged line, or is it normal to have a sealed system? Quote Link to comment Share on other sites More sharing options...
TheNeedForZ Posted November 28, 2005 Share Posted November 28, 2005 Are you sure the vapor can actually exit from the hose you are referring to? I mean if you assume vapor can exit from it while it can't for some reason.... If the venting is too slow, then you will still have pressure. Like blowing air thru a thin, long straw. Quote Link to comment Share on other sites More sharing options...
bradz240 Posted December 6, 2005 Share Posted December 6, 2005 I experience the same pressure build up in my stock '83. Sometimes the fuel pump starts to make a loud buzzing sound. When I remove the fuel cap there is always a pressure buildup present when the fuel pump makes this excessive noise. I have replaced the fuel pump, and regulator, fuel filter, eliminated a kink in the return line near the tank and checked the purge control valve on the charcoal canister. I'm still looking for the solution. If anyone has any other ideas I'm listening. Quote Link to comment Share on other sites More sharing options...
Here comes trouble Posted December 7, 2005 Share Posted December 7, 2005 http://pg.photos.yahoo.com/ph/larryjohnson97438/detail?.dir=8223&.dnm=879b.jpg&.src=ph My old silver Z had same problem of excess pressure that got worse. To keep it running I ran half a tank with gas cap off. Engine would hardly run after a few years. Never found the problem. When I turned the Z in to the GTO 250 project.. I removed the fuel tank and found it super clean.. blew the fuel lines etc etc etc. I suspect a fuel pressure regulator problem. I will eventually parts change until it runs right. This is not a normal pressure build up but something wrong in the FI fuel delivery. On my re-build of the 250 Project... I will install a fuel pressure guage which should be on every L 6 FI engine for diagnosis Here is the 250 GTO photos and somewhere in there is a pic of a fuel rail, pressure guage and 60 mm throttle body http://pg.photos.yahoo.com/ph/larryjohnson97438/album?.dir=8223&.src=ph&store=&prodid=&.done=http%3a//photos.yahoo.com/ph//my_photos Quote Link to comment Share on other sites More sharing options...
bjhines Posted December 8, 2005 Share Posted December 8, 2005 I did not come back to this thread soon enough.... The flow control valve (mounted on the left inner front fender...is key to allowing the system to "vent".... But it only allows gasses to enter the tank...not exit..... Your fuel filler cap also allows air to escape if it builds up more than just vapor pressure...obviously the fuel pump is not going to vent gasses...maybe gasoline... Soo...unless you have multiple failures of all the above parts....you cannot get a "higher than normal" pressure buildup in the fuel system. Quote Link to comment Share on other sites More sharing options...
2126 Posted December 8, 2005 Share Posted December 8, 2005 I believe it's a normal thing for any CLOSED fuel system. As said, the fuel vapors do expand and with no where to go it will build some amount of pressure in the tank. Remove the fill cap.....release the pressure! Quote Link to comment Share on other sites More sharing options...
bradz240 Posted December 8, 2005 Share Posted December 8, 2005 Mine buids up pressure on long trips. When the fuel pump starts making lots of noise there is always pressure in the tank, let it out and the fuel pump quiets down. I believe the s130's fuel cap is vented to allow vacuum release but not pressure release. Quote Link to comment Share on other sites More sharing options...
cygnusx1 Posted December 8, 2005 Author Share Posted December 8, 2005 Nissan put a vapor cannister on that steel fuel line on the right front inner fender. Obviously, that was a place to vent vapors from the tank. Nissan, I assume, intended it to vent only under certain conditions to comply with fed emmisions. They controlled 'when' the tank was vented into the carbon cannister with a vacuum controlled valve on the cannister. I assumed, and I could be wrong, that once you remove the carbon cannister and the valve, leaving the steel vent line open to the engine bay, the tank would be vented to atmosphere full time. This would never allow pressure to build in the tank....apparently that Nissan vent line is either clogged or has another valve in it closer to the tank. Quote Link to comment Share on other sites More sharing options...
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