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Discussion Starter · #1 · (Edited)
Can anyone explain the Evap system operation for the 2jz-gte ? Looking at the diagrams it doesn't make too much sense offhand, but there must be a method to the madness ...
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and
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Looking at these, it seems that vapors are drawn from the fuel tank through the charcoal canister and into the pre-turbo side of the intake. Fine, reasonable.

But the 3rd line goes off towards the intake chamber/throttle body. It tees off, one side going via a check-valve to the throttle body. The check-valve is to prevent boost pressure from pushing BACK into the charcoal canister. Makes sense, since this is the potentially pressurized side.

The other side of the tee goes through the Evap vsv and into the intake chamber. This TOO will see both vacuum and boost pressure, so the vsv only opens when the intake is under vacuum, right ? OK. Those two sides can see different vacuum/boost values because of the throttle blade - when the throttle closes the left one (with check-valve) sees higher pressure while the right one (via vsv) can see vacuum.

What's the point of all that though ? Why are the THREE different routes to the intake tract from the charcoal canister ? One under vacuum all the time, one that sees vacuum only or no connection (due to check-valve) and one that sees vacuum only or no connection (due to vsv).

As I set up the drive-by-wire throttle for the I'm finally going single! project here, I'm wondering how best to set up the Evap system. The Haltech Elite 2500 has an Evap function, but I'm not sure of how/when it operates.

Any ideas ? I definitely want to keep the Evap system, I've been around a couple of Supra without and the gas smell is pretty obnoxious. I suppose it's easy enough to put in a bung on the air-filter tube before the turbos for the bare line, but I don't think I've seen anyone else actually doing that. I'm thinking to simply cap off port B (was to pre-turbo intake) and route the other one (port A) through a vsv to the intake chamber. The Elite 2500 will control the vsv.

How do you all have your charcoal canister hooked up ?
 

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Just a guy who loves cars
94' Turbo, Targa, 6 spd, Ren Red.
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This is a great question. I just reinstalled my charcoal canister due to the aforementioned fuel smell. I have the fuel line going in and the other two ports capped off. But, after studying the drawing you posted I question if I should not provide a vacuum source to one of the other ports. I had a lot of trouble figuring out which port the fuel line went to anyway since mine had been completely removed. I think I may try to run one other port to the check valve side.
 

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Basically, vapors go from the tank to the canister, and then it is either let into the intake manifold via the vsv (ecu controlled) or on part throttle situations from the ported vacuum on the throttle body.
There is a check line to prevent pressurizing the canister under boost for the throttle body line, for the vsv the ecu will not open the evap vsv under boost.

I want to say the third line on top of the canister is a fresh air in to replace the vapors in the canister with fresh air when the vapors are pulled into the intake manifold via the vsv or ported line, so you aren't pulling a vacuum on the fuel tank (this can lean out or mess with your AFRs).
this line should go to the intake piping behind the maf, it should not see positive pressure.

If you cap off the ways to vent the can, you will get a large gas smell every once in a while because the canister has an emergency vent on it, so when it builds up enough pressure (which it shouldn't be doing), it will vent for safety, usually this is like a hose that runs to the fender on the bottom of the can on toyotas.
On cars that have it setup like this they can get really bad on hot days, I would recommend keeping some sort of way to vent the canister properly.
 

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I removed the line going to the factory turbo area and left it uncapped.

I left the line going to the fuel tank.

I left the line going to the intake manifold.

No fuel smell and i think its pulling vapors when the manifold is in vacuum.

I tried to blow into the line at the upper intake manifold to see if vapors were being forced back into the cansiter under boost but it seemed like there must be a check valve in the canister. Would be nice to relocate it.
 

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If you have the line going to the intake manifold and that section is stock it should be pulling in vapors fine. It is when you block that line the canister starts to self vent.

Yes, the canister does also has a check valve built into the top of the line going to the intake.
I think that is the last resort and even the n/a ones have the built in check valves so could be for other safety reasons also.

Also note, if you have the line that was going to the intake piping behind the maf removed and uncapped like you said, if you are still running a maf you are getting unmetered air into the system when it is pulling the vapors out of the canister. you might not really notice it though the ecu can probably compensate for it. If you are running a map sensor then it can be uncapped like you have it.
 

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Remove all of that crap and put a filter on the line coming from the gas tank to the engine bay so that tank can breath.

Steve
 

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Discussion Starter · #8 ·
The line from the fuel tank goes into port C on the canister. Air should flow easily to ports B (intake) and A (throttle-body via check-valve and intake chamber).
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Still doesn't explain why there are THREE paths to the intake stream. Port B to the after-MAF intake, always under vacuum. Port A to BOTH the throttle-body and intake chamber. If the ecu is controlling the vsv to only open while the engine is under cruise/idle conditions (so pullingvacuum) then why add the extra line via check-valve to the throttle-body ?

Meh. Asked Haltech - they can't actually SAY anything since it's emissions-related. But the EVAP function opens a vsv under cruise/idle conditions, so going to do what I outlined above. Cap off port B, run the line from port A to a vsv then to the intake chamber. Done.
 

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One port (B maybe) is the inlet/vent for the canister, it should go to pre turbo intake piping.
The other port (A maybe) is the outlet to the intake manifold, which has 2 paths: one vsv controlled and one mechanically controlled... older cars just had the mechanical one on the throttle body, newer cars just have the vsv... toyota for a long time did both all through the 90's and for a while after. they both do the same thing more or less.

Pre-turbo intake piping and the post-turbo intake manifold are very very different parts of the intake stream, the intake manifold sees full vacuum, and your pre turbo intake piping only ever sees a part of that vacuum.

That is kind of the same concept as your pcv system, one valve cover has a line going to the pre-turbo intake piping for fresh air to go into the crank case to replace the crank case vapors that go out the other side and into the post-turbo intake manifold, again to burn up the crank case vapors. The pcv also has a check valve to prevent air going in the other direction just like the canister has.

So both those ports really don't go to the same place, so if you cap off port B then you could have a problem with the system not operating properly and maybe even pulling vacuum on port C. The non turbo canister just has 2 ports so maybe there is something else going on with the GTE canister and port B.

I haven't really ever seen a case where capping a port on a evap canister was a good idea, usually people just do what 1A1 said above but I like to keep those systems operating like stock whenever possible.
 

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Discussion Starter · #10 ·
Pre-turbo intake piping and the post-turbo intake manifold are very very different parts of the intake stream, the intake manifold sees full vacuum, and your pre turbo intake piping only ever sees a part of that vacuum.
Right - pre-turbo is always in vacuum. Post-turbo see both vacuum and boost, so access to the fuel-tank line must be controlled, either via check-valve or ecu-controlled vsv.
That is kind of the same concept as your pcv system, one valve cover has a line going to the pre-turbo intake piping for fresh air to go into the crank case to replace the crank case vapors that go out the other side and into the post-turbo intake manifold, again to burn up the crank case vapors. The pcv also has a check valve to prevent air going in the other direction just like the canister has.
Hrm - never thought the fuel tank needed a source of air ... How much of a source would it be if it's always in vacuum ? I suppose if it's less negative pressure than post-turbo it could be a source.
So both those ports really don't go to the same place, so if you cap off port B then you could have a problem with the system not operating properly and maybe even pulling vacuum on port C. The non turbo canister just has 2 ports so maybe there is something else going on with the GTE canister and port B.

I haven't really ever seen a case where capping a port on a evap canister was a good idea, usually people just do what 1A1 said above but I like to keep those systems operating like stock whenever possible.
 

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The pre-turbo hardly has any vacuum, but since the post-turbo side has much more vacuum the air will always want to go to the side with more vacuum, doesn't matter if there is a crank case or a canister in between the sources. The canister is the part that needs the air line not the tank (tank vents out).
 

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Discussion Starter · #13 ·
From the diagrams above :
  • port A : goes to intake chamber via vsv and throttle body via check-valve
  • port B : goes to pre-turbo intake
  • port C : goes to fuel tank
Port C will flow to both ports A and B - makes sense, allow fuel vapors to escape.
Neither ports A or B can flow back to C (fuel tank). So the ONLY source of air for the canister is from the fuel tank, which in turn can replace air via the Fuel Breather Pipe, seen below. Well, it might be able to go into the canister itself, from port A to B or B to A, but now back to the tank on port C.
White Organ Human body Jaw Organism

So the tank doesn't need the Evap system to allow air back into the tank - it already has facility for that. Why would the canister need an air source like port B/pre-turbo (that would be under at least some vacuum all the time) when it has a perfectly good one from the tank via port C (fed by the breather at the filler neck) ?
 

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The breather at the filler neck only vents air with the gas cap off as you pump fuel in. Once you put the gas cap back on, that inlet is sealed and it's job is done until the next time you fill up.

There is another breather for the tank while the car is running, the hose for it is labeled "EVAP hose" above.

Al
 

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Discussion Starter · #16 ·
Yup port C is the line from the tank. Only allows air FROM the tank into the canister and then OUT of ports A and B to the intake spots. I would think the only way for vapors to get from the tank to the canister is if the tank was able to ingest air via the tank breather or the cap. I don't see any other path. It can't pull from the canister.
 

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Pretty sure it goes to port C.

The tank vent has to allow air to go in or out, there is a huge check valve device inside the tank. Air goes into the tank as fuel is being used, and air goes out as the fuel expands and heats up.

I am missing the VSV canister part of the system, that got removed with the EGR. After I get home from a summer drive, with the fuel heated from the fuel pump, you can hear the canister making a whistling sound for a while, and there is a vacuum when you take the gas cap off. Of course, if you relieve the pressure at the cap, the canister stops whistling.

I need to figure a way to put the VSV canister back in. Very low priority as I'm not removing the intake manifold just for that shit, lol!

Al
 
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