Thread: Low Gas Tank Pressure? [Fixed!!!!!]

Alright I've noticed this for a long time, but when I go to fuel up, unless I have been driving for about 30 minutes I wouldn't have a hissing sound when I open the gas cap.

I replaced the gas cap, and that helped a little but still happens a lot.

This is on my 99 SE-L

I have a 2000 P11, and it was standing in my garage for over a month without being driven, when I opened the gas cap I heard pressure being released and gas going down the tube (vacuum was holding gas in the tube I guess).

In my car, I let it stand for an hour or two and the hissing is non existent.

I've looked under the car to see if there were any noticeable leaks, or cracked hoses. And so far I keep on coming back to the black box... the Vapor Canister (Charcoal Canister) and Purge Valve.

I've had an issue with the Vapor Canister and Purge Valve on my old 200sx. It would be holding too much pressure, thus when I would go to fuel up the gas pump would shut off like it was full. The pressure would cause that.

Now I found a web page with some info about the canisters that are found in the engine bay, Pre 98 200sx's: How Nissan Evaporative Systems Work

The vapor canister and purge valve are not cheap, about $350 total

I did test the Purge Valve by connecting it to the car battery, and it would close shut when electricity is applied. So that is why I am doubting it is the Canister or purge valve.

To add, the vapor canister didn't seem to have any liquids inside of it (sometimes gas can flow into the vapor canister, thus giving you about one or two more gallons of gas that you can fill into the car.

Any ideas? I think I might need to take a look at the gas tank, but before I open her up, wouldn't mind hearing any other ideas


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Also is this valve supposed to be a one way valve? It is found right under the Intake by all the emissions piping. (Just found my answer in the FSM, circled the needed information below)






Finally Fixed!!!

the vacuum can be checked via the evap port with a green cap on the driver's side of the engine bay. You hook a tester up there and you can apply vacuum to check for leaks. Also, if you hook up a smoke machine to that port you can find leaks. Few people have the equipment to check this stuff, so you are stuck with taking it to the dealer most likely.

But I would def check all of your hoses for leaks and cracks. It seems like it may be tough to find but you are having troubles with gas evaporating right? If so it is most likely a leak in the system. Do you get a code p044x? If not then do you smell gas anytime?

Yep like you said not many people have this testing equipment, what makes it worse is not many people have the 98-99 SR20's so not as much information to search through .

I went through most of the EGR hoses and blew in them listening for vacuum leaks hahaha. They seemed to be fine, except for that one way valve. Apparently it is not so one way!

Any ideas on where I can pick up a new one?

No codes, gas smell is non-existent, only when I was running rich the gas smell was bad.

Now from what I understand, the Vapor Canister goes to the intake manifold. Thats where the fuel vapors and air get purged to. If my one way air valve is leaking air out, then that would explain where some gases would go hehe.

Now with the one way valve, which way is the air supposed to travel? The FSM page says "Colored Side Should Face the Vacuum" Does that mean that the intake Mani sucks the air but cannot dump any back?

I do believe my gas is just evaporating. If I leave the car standing for couple days in the sun (and not drive it), then when I got to fuel up I would get record low MPG's. Like 16mpg etc.

Thanks for all of your help Coheed, both in this thread and the other ones

i swear you worry to much about stuff lol.. specialy to save some gas

^^^ what do you expect? his engine is dying!!

Guys I think I finally found it!

Purge Bypass Valve, or Vacuum Cut Valve (Part # 17372-3M200)
http://www.nissanhelp.com/Ownership/Bulletins/2002/NTB02-033.htm

When I went to take it off, a piece of plastic just broke off!

When I would turn off the car, I would hear a whistle like sound, from the back of the car. Today I blew into the Vapor Canister, and heard that sound, took of the gas cap, and blew, and no sound.

I listened till I heard it coming from the valve... Now I also had gas in the tube on the gas tank side! There shouldn't be gas in there.

I found the part, but it's like $100 at the stealership, anyone know where to get it cheaper?

Also, I took the valve off my wife's 2000 P11, the part number for that valve is 17372-1W200. When I took the gas tank side hose of my wife's P11, it was blowing vapors from the gas tank like crazy! I had to open the gas cap to release the pressure quicker!

nice man. Good to see you are making progress. At least you have the resolve to really tackle a project like this. They can be a pain to find. Maybe greg can get it cheaper for you? try some auto parts stores online and see if anyone can get it, or you can just raid a junkyard car. The GA engines have the same setup in the back iirc. The one way valve can be picked up anywhere. Most parts places will have one in stock for a couple bucks.

Thanks man

So after all it's not always the engines fault for crappy performance and MPG's ha.

Anyway, I replaced that Vacuum Cut Valve with my wife's P11 one hehe. Her car needs inspection and can't be driven in VA yet, so I scavenged it haha.

I installed it and blew into the Vapor Canister's Purge valve, and once again that whistle like sound came out of the Vacuum Cut Valve. While it didn't do so on the P11.

I am thinking it might be the pipe that runs into the gas tank, it could possibly be clogged up thus making that sound. I put everything together and fueled up, will see how it goes after I drive the car until next fuel up

As for the one way valve, I went to the Autozone and did pick a new one way valve, this one was for GM hehe. The only thing is, when I took off the stock one and testing it out it actually was working better then the Autozone one LOL.

Reason for me thinking it was bad to begin with is because when I blew into it, I forgot to suck in the air to see if it would lock up haha.

Dude, I don't even have that valve on my car man.

Really? You should, it's to the left of the vapor canister.

I think my 98 GA 200sx used to have the valve, I know for sure it has the vapor canister.