fuel tank vent hose help

[connor116]

Hello!
So I am in the process of a 2jz swap and have just removed the stock engine. I have been cleaning up the engine bay and had no idea what to do with the vent hose from the fuel tank. Currently, I have it cut at the firewall. I did a lot of searching and it looks like there is a forum post where the OP explains that you need to remove the check valve because there is no longer a vacuum on the check valve and therefore it wouldn't work properly. Other people say that it is fine to leave the check valve and that it works just fine without being connected to the charcoal canister.

Any insight to this issue would be appreciated!

Thanks!
- Connor

[Silv1401]

Not sure how the setup on the s13 is, but on the s14 we have a vacuum-actuated check valve near the manifold, and the charcoal can in the rear bumper, which then has an electronic "vacuum assy" that modulates glow from the tank to the canister.

Now I just went though my engine bay and fuel system and cleaned it up as well. My s14 came with a KA-t, and the previous owner never touched the fuel emissions gear. I found the vent line from the tank to the canister was filled with charcoal, because of the positive pressure from the turbo. So I decided to delete the canister-to-intake line, and the electronic "vac assy" module. Then I ran the black vac-actuated check valve on the tank vent line, but without a vac line. That check valve requires less than 1psi to crack open (tested with a mityvac) in the flow direction. That allows excess tank pressure to escape. You can run that output side to atmosphere or the charcoal can. Heads uo: gas odors will probably become present in either case.

Hope that helps.

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[connor116]

Originally Posted by Silv1401

Not sure how the setup on the s13 is, but on the s14 we have a vacuum-actuated check valve near the manifold, and the charcoal can in the rear bumper, which then has an electronic "vacuum assy" that modulates glow from the tank to the canister.

Now I just went though my engine bay and fuel system and cleaned it up as well. My s14 came with a KA-t, and the previous owner never touched the fuel emissions gear. I found the vent line from the tank to the canister was filled with charcoal, because of the positive pressure from the turbo. So I decided to delete the canister-to-intake line, and the electronic "vac assy" module. Then I ran the black vac-actuated check valve on the tank vent line, but without a vac line. That check valve requires less than 1psi to crack open (tested with a mityvac) in the flow direction. That allows excess tank pressure to escape. You can run that output side to atmosphere or the charcoal can. Heads uo: gas odors will probably become present in either case.

Hope that helps.

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Thank you for the reply! So another quick question then, so the check valve allows for positive pressure in the gas tank to be released, but will the check valve also allow flow in the other direction? If not, how will the negative pressure in the gas tank be equalized?

[Silv1401]

Well you can double-check. Take the check valve off and blow on each side. My valve I can blow easily through one side, but not at all through the other, unless I put vacuum on the vac line, then I can blow through both sides.

That said, the gas cap on an s13 has a one-way check valve to allow air in so as to displace vacuum. S14s have a 2-way valve, though.

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[connor116]

Originally Posted by Silv1401

Well you can double-check. Take the check valve off and blow on each side. My valve I can blow easily through one side, but not at all through the other, unless I put vacuum on the vac line, then I can blow through both sides.

That said, the gas cap on an s13 has a one-way check valve to allow air in so as to displace vacuum. S14s have a 2-way valve, though.

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That's great info thank you! So I am actually looking to get an s14 fuel cap, but it seems that there are multiple models of them. Do you happen to know if all of the s14 gas caps are 2-way valves? And if a s14 gas cap fits the s13?

I appreciate it!

[Silv1401]

Ooh, I do not know for 100%. My s14 is a 98, so I can't really speak for for the Zenkis. But to the best of my knowledge, s14s all have the same cap. I would just find a part number and see if it applies for all 95-98 models. As for thread size, from a common sense standpoint, there is zero reason why Nissan would change the threads. I'm pretty sure I've read old posts on Zilvia where s13 guys swapped to s14 caps.

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[connor116]

Originally Posted by Silv1401

Ooh, I do not know for 100%. My s14 is a 98, so I can't really speak for for the Zenkis. But to the best of my knowledge, s14s all have the same cap. I would just find a part number and see if it applies for all 95-98 models. As for thread size, from a common sense standpoint, there is zero reason why Nissan would change the threads. I'm pretty sure I've read old posts on Zilvia where s13 guys swapped to s14 caps.

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Massive thank you for your insight and information sir!

[Silv1401]

No problem, man. Good luck with everything!



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[Kingtal0n]

I would read the fsm for your car very carefully because there are all kinds of filthy stuff shoved under the quarter panel near the gas tank on an S14 that needs to be dealt with






Im not being cryptic on purpose I literally need to do the same thing on my last 20 cars but never seem to get around to it