David P Posted October 16, 2015 Share Posted October 16, 2015 Try reading the Workshop Manual, there it is clearly explained. Quote Link to comment Share on other sites More sharing options...
Scott Posted October 16, 2015 Author Share Posted October 16, 2015 Try reading the Workshop Manual, there it is clearly explained. Again, got any references? I've just gone through the whole SFI manual and I can''t find anything mentioning a positive pressure. Are you being deliberately obtuse and obscure here? Surely you could just reference your source concisely and the point would be made? Quote Link to comment Share on other sites More sharing options...
Ian C Posted October 16, 2015 Share Posted October 16, 2015 It'll be on the same page that proves 35mpg at 100mph is possible Quote Link to comment Share on other sites More sharing options...
Tricky-Ricky Posted October 16, 2015 Share Posted October 16, 2015 Of course you also have to take into consideration the constant return of fuel to the tank, but even so unless there was a way of negating positive or negative pressure it would impact on fuel flow. You will actually have both positive and negative pressure in the tank, it needs to be vented in a way to reduce both over and under pressure, as when heated and fuel slosh happens it will generate positive pressure, conversely when the fuel is cooled and fuel demand is high it will generate negative pressure. AFAIK its not just down to the charcoal canister, that is simply a way of containing the vapor, and then sucking it into the engine to be burnt, its obviously valved to provide engine vacuum at the appropriate time, modern setups have a ECU controlled valve to purge the charcoal canister by I am sure its done more simply on the Supra. Quote Link to comment Share on other sites More sharing options...
Scott Posted October 16, 2015 Author Share Posted October 16, 2015 It'll be on the same page that proves 35mpg at 100mph is possible It's looking that way. See, I've just gone through the Emission control manual and I can see where what it says can be misconstrued. The cleaning of all vacuum equipment is done using positive pressure from the opposite end of the one way valve. However, it clearly states that the use of the charcoal system is "to prevent the atmospheric release of blow-by gas containing HC". The only way to prevent atmospheric release is to create a vacuum. The BEST way of doing this on our engine is to use the vacuum pressure created from the intake manifold, which is exactly what the charcoal canister is connected to. The trouble is that the vacuum will increase as the fuel is used, hence why there's a pressure relief valve (-2psi). It all makes perfect sense when it's a vacuum, it makes absolutely no sense when the tank is positive pressure. Every car I have ever known runs on a vacuum for this very reason, running positive would be very unique if that's the case. I'm happy to prove it by putting a vac/pressure gauge onto my tank breather line to see what happens if someone wants to supply one though Quote Link to comment Share on other sites More sharing options...
David P Posted October 16, 2015 Share Posted October 16, 2015 Nothing of the sort, yet at this time my workshop manuals are on loan to A. N. Other. I don't tell lies, but if you are so determined to prove me wrong, you will have to keep reading until you prove me correct. Quote Link to comment Share on other sites More sharing options...
Scott Posted October 16, 2015 Author Share Posted October 16, 2015 Nothing of the sort, yet at this time my workshop manuals are on loan to A. N. Other. I don't tell lies, but if you are so determined to prove me wrong, you will have to keep reading until you prove me correct. You have me confused. I'm not that person. I simply want to be right and will happily be proven wrong in order to know the right answer. I'm an engineer by heart, head and everything else that goes along with the job. I like to take things apart and figure out what makes them work and how they work, regardless of if I break them in the process. Anyway, character flaws aside...... I've worked on a LOT of fuel systems on varying technology and positive pressure on a gas removal system doesn't make any sense to me at all. This is purely my experience and thoughts based on said experience. I am very happy to be schooled with proper reasoning, what you have said makes no sense to me though so I would like credible sources so that I can understand the system myself. Quote Link to comment Share on other sites More sharing options...
Tricky-Ricky Posted October 16, 2015 Share Posted October 16, 2015 If you go by your original post starting this thread, you asked about what to do with the tank vent pipe that goes to the charcoal canister, now if your saying there is a constant vacuum applied to this all the time the engine is running, then how do you explain the lack of any fuelling problems with all the Supra running minus the canister with no engine applied vacuum? Quote Link to comment Share on other sites More sharing options...
David P Posted October 16, 2015 Share Posted October 16, 2015 Just pull off the tank hose of the charcoal filter when it is "ticking" and you will find that it blows, not sucks. Quote Link to comment Share on other sites More sharing options...
Scott Posted October 16, 2015 Author Share Posted October 16, 2015 If you go by your original post starting this thread, you asked about what to do with the tank vent pipe that goes to the charcoal canister, now if your saying there is a constant vacuum applied to this all the time the engine is running, then how do you explain the lack of any fuelling problems with all the Supra running minus the canister with no engine applied vacuum? I don't think there would be any fuelling problems at all to be honest. It's a standard feature from toyota for removing hydrocarbons (or something of that ilk) to keep the green brigade happy. If it isn't connected then it will simply mean that the vacuum in the system is almost nil. I didn't think for a second this would cause any issues but I thought I would ask to be on the safe side. Blanking it off makes sense to me as I'm just incoherently paranoid about fuel or fuel vapour coming out and being ignited, that was the only reason I asked the original question. The discussion has gone the way of the charcoal canister, etc, which is a far cry from my initial query but I'm very eager to learn more about this particular system so was more than happy to continue the discussion. Just pull off the tank hose of the charcoal filter when it is "ticking" and you will find that it blows, not sucks. I can't unfortunately, I don't have it any more. This isn't referenced material that you were speaking of though. People state a lot of "facts" when they are often simply misguided or mistaken, this isn't a lie..... it's simply a misunderstanding. I'm not saying you are lying, I'm simply saying that you could be wrong. Quote Link to comment Share on other sites More sharing options...
Chris Wilson Posted October 16, 2015 Share Posted October 16, 2015 David is a knowledgeable chap, but I have to say he is mistaken here. I haven't even read the sections of the workshop manual that may refer to this, but there is NO WAY a manufacturer would allow the normal build up of a positive above atmospheric pressure to build in a fuel tank. Sorry David, it may be that the manual is unclear, and pressure versus atmospheric can be written in obtuse language, but I stand my ground here Quote Link to comment Share on other sites More sharing options...
Scott Posted October 16, 2015 Author Share Posted October 16, 2015 David is a knowledgeable chap, but I have to say he is mistaken here. I haven't even read the sections of the workshop manual that may refer to this, but there is NO WAY a manufacturer would allow the normal build up of a positive above atmospheric pressure to build in a fuel tank. Sorry David, it may be that the manual is unclear, and pressure versus atmospheric can be written in obtuse language, but I stand my ground here This is my experience too, it's the same with jet engines. Positive is usually a fault in my experience, always considered "bad" I won't write off that the potential is there though, I'd just need to see it to believe it. Quote Link to comment Share on other sites More sharing options...
David P Posted October 16, 2015 Share Posted October 16, 2015 I really can't understand why it can't be understood that without positive pressure the charcoal filter would be an ornament? When I get my manuals back and can be arsed to find again and read again what others apparently can't, I'll take a pic and post it. Quote Link to comment Share on other sites More sharing options...
Scott Posted October 16, 2015 Author Share Posted October 16, 2015 I really can't understand why it can't be understood that without positive pressure the charcoal filter would be an ornament? When I get my manuals back and can be arsed to find again and read again what others apparently can't, I'll take a pic and post it. No it wouldn't, it would work like a bong! - - - Updated - - - I really can't understand why it can't be understood that without positive pressure the charcoal filter would be an ornament? When I get my manuals back and can be arsed to find again and read again what others apparently can't, I'll take a pic and post it. No it wouldn't, it would work like a bong! Intake manifold powered. Quote Link to comment Share on other sites More sharing options...
David P Posted October 16, 2015 Share Posted October 16, 2015 Without engine vacuum the charcoal filter still "gurgles", this is relieving positive tank pressure and filtering out the fuel vapours. All you need to do is pull off the tank hose to prove it. Quote Link to comment Share on other sites More sharing options...
Scott Posted October 16, 2015 Author Share Posted October 16, 2015 Without engine vacuum the charcoal filter still "gurgles", this is relieving positive tank pressure and filtering out the fuel vapours. All you need to do is pull off the tank hose to prove it. It would gurgle with a vacuum as well remember. Especially when heat soak started to come into play. There's multiple perspectives to every situation. It'll be easy for me then. I've blocked off the tank vent so when I take the silicone blank off it'll blow out instead of sucking in Will update after a run! Quote Link to comment Share on other sites More sharing options...
Tricky-Ricky Posted October 16, 2015 Share Posted October 16, 2015 I'm just incoherently paranoid about fuel or fuel vapour coming out and being ignited, that was the only reason I asked the original question. The discussion has gone the way of the charcoal canister, etc, which is a far cry from my initial query but I'm very eager to learn more about this particular system so was more than happy to continue the discussion. . LOL! you wouldn't have wanted to be around me in my bike building days, as you could often find me washing parts in petrol complete with a lighted cigarette in my mouth...and surprise surprise I never once set fire to anything, well at least not unintentionally:D Nothing wrong with a bit of healthy discussion:) Quote Link to comment Share on other sites More sharing options...
Scott Posted October 16, 2015 Author Share Posted October 16, 2015 LOL! you wouldn't have wanted to be around me in my bike building days, as you could often find me washing parts in petrol complete with a lighted cigarette in my mouth...and surprise surprise I never once set fire to anything, well at least not unintentionally:D Nothing wrong with a bit of healthy discussion:) That doesn't worry me too much I use jet fuel quite a lot to clean parts etc (works well on carbon). I don't worry about a bit of flame, easy to control, it's more the ignition without me knowing that I'm scared of. Inlet to the tank has me uneasy Quote Link to comment Share on other sites More sharing options...
herbiemercman Posted October 16, 2015 Share Posted October 16, 2015 For me it is negative, not taking sides, just an observation of filling my car up for 20 years. Quote Link to comment Share on other sites More sharing options...
Nic Posted October 17, 2015 Share Posted October 17, 2015 Service manual http://www.mkivsupra.net/vbb/content.php?51-Repair-Manuals Quote Link to comment Share on other sites More sharing options...
Digsy Posted October 17, 2015 Share Posted October 17, 2015 I didn't read the whole thread, but: An evap system (purge system) is there to prevent light hydrocarbons from venting direct to atmosphere. Certain countries require a SHED test in which the evaporative emissions of a non-running car are measured over a period of time in a sealed environment. SHED tests are more strict in the US than elsewhere, and the diagnostic requirements for the purge system are more strict. Fuel vapour which evaporates naturally from the liquid in the tank is routed through the charcoal cannister, which is connected to the atmosphere. The carbon pellets inside the canister absorb the fuel vapour and store it. The size of the canister and the working volume of carbon is calculated from the size of the fuel tank, the rate of vapour generation (from experiment) and additional factors in case the system has onboard fueling vapour recovery (where vapour pushed out of the tank by refueling is collected in the purge canister). Sometimes there is a pressure check valve which does not allow the tank to vent atmospehere until it is above a certain pressure. This pressure inside the tank reduces the amount of vapour that evaporates off and so in turn drives a smaller evap canister than would be required by a system that always vents above atmospheric pressure. Such vehicles tend to emit a puff from the fuel tank when the filler cap is removed. I once did a bench marking study of 19 vehicles all of which exhibited some kind of "puff" from the tank and found that 70% of them were from Japanese manufacturers, and all had evap canisters that were smaller than the sizing formula would suggest. Federal vehicles have an electric shut off valve on the line to atmosphere which enables the system to be closed off for diagnostic testing. The valve is closed, the purge valve is opened and the system is drawn down to below atmospheric pressure by the engine. A pressure sensor in the system checks for leaks. The fuel vapour stored in the canister is periodically purged by opening the valve connecting the canister to the intake manifold (for purging off boost) or sometimes to further up the intake system (for purging on boost). During purging, fresh air is drawn into the canister through the carbon pellets via the line to atmosphere. The ECU knows when it is purging and how much additional air / vapour is entering the plenum and so fueling issues are avoided. Quote Link to comment Share on other sites More sharing options...
David P Posted January 14, 2016 Share Posted January 14, 2016 Scroll down to DI 75 for Workshop Manual info and trouble shooting of pressurised fuel tank system. http://www.mkivsupra.net/vbb/content.php?61-Diagnostics Quote Link to comment Share on other sites More sharing options...
a98pmalcolm Posted January 14, 2016 Share Posted January 14, 2016 I removed the charcoal tank a while back now and redirected the fuel line into the wheel arch line that was connected to the bottom of the tank. Never got a fuel smell. Until recently after my remap with bigger injectors I have a potent smell, Especially when my blowers are on. This could be with more fuel its using the fuel vapour is more? Just an unlikely thought so I'm going to block the fuel tank vent pipe as suggested by David, but for a few days and see if theres a difference. If not I will reconnect the rerouteing pipe. Were does the line from the bottom of the charcoal tank go to any way?? Quote Link to comment Share on other sites More sharing options...
David P Posted January 14, 2016 Share Posted January 14, 2016 (edited) That's the original water drain pipe from charcoal filter, it is an open pipe that will now be exiting fuel vapours at centre front cross member. Not too far from where you might fit a screamer pipe. Edited January 14, 2016 by David P (see edit history) Quote Link to comment Share on other sites More sharing options...
a98pmalcolm Posted January 14, 2016 Share Posted January 14, 2016 That's the original water drain pipe from charcoal filter, it is an open pipe that will now be exiting fuel vapours at centre front cross member. Not too far from where you might fit a screamer pipe. ok thanks david. blocked off bow. will.see how it goes Quote Link to comment Share on other sites More sharing options...
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