Question about 1985 Nissan 300ZX

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In my 1985 300ZX vapor pressure builds-up in the gas tank, and when the gas cap is removed a considerable amount of vapor comes out. Why is this? Thank You I began to notice few months ago,I use the car possibly once / week. I thought it may be the evaporator canister filter, I removed it but it seems a sealed unit.. There seems somewhat of a removable base, but it does not budge. Afraid of breaking it. Hose lines seem OK. I also installed a new gas cap, same thing occurs.

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It sounds to me as if, when refuelling, you put gas in right the hilt. and keep filling it up. this is not good practice as it causes more problems then its worth. It could also the purge solenoid not purging the raw vapors from the tank to the atmosphere. i would get that looked at and the unfortunate part is that's a dealer diagnosis. good luck!

Posted on Aug 24, 2010

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Posted on Jan 02, 2017

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Why check engine light and code P0540 Large Evap Leak


did you reset codes after every repair ? is it a newer car ? there is a sensor in canister called a netural pressure vapor sensor they tend to leak or stick .causing evap codes , I chased the same code ,it would go out for about a week then come back in my case it was the new gas cap it was the wrong one for my car. it keeped building pressure in gas tank . and could hear it hissss when I would open it fuel up .

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Much preasure in gas tank when removing filler cap


Hello the pressure is supposed to build up as the fuel produces vapors which are trapped in your gas tank. There is nothing to worry about - all this is a good sign that your tank is well sealed.

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I am not sure I understan tghe question. You should not have a lot of pressure in the tank. There are hoses that capture any vapors that are in the tank and eleviate pressure build up.
Most often I have found the engine light on because of gas tank vent, such as loose
or bad gas cap or the vent valve stuck open. The computer does a cycle ever so often
and maintains the vent pressure build up in the gas tank and vapor canister, and if the purge valve sticks open the computer gives a check engine light and code as the pressure is not in the vapor storage tank when called for.
If your worried about no pressure at all then I would change the gas cap and see if this helps

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Fuel problems with '98 Chrysler Concorde


Easiest diagnosis and fix is to replace the gas cap. Too many people do not recognize the modern gas caps are not like the old 70's where you had carbeurated engines. With the new systems a proper vacuum (you are spot on) is required. Since you can correct this problem by manipulating the gas cap it doesnt sound like anything with a vacuum hose, etc in the engine compartment. Sounds like the gas cap has failed and is not venting/passing air as it should. A valve in the gas cap is set at a certain pressure rating for your vehicle and all vehicles to vent gas vapors and allow air into the tank.. One to prevent explosion due to vapor build up and two to allow a certain amount of air into the tank. This valve is defective or broken on your cap. A new cap is about 11 dollars at the local parts store.

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Gas pressure build up in gas tank there is a sound that it make s and i can here pressure releas for the gas cap


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Check engine light on 2001 chrysler 300m. The code says it has to do with either my gas cap not being tight or some sort of fuel fumes. I'm sorry I don't know the codes.


Make sure that the gas cap is the correct one. If the gas cap was replaced with a different style or a locking cap this will set off the check engine light. It can tell there is a problem because it measures the built-up pressure in the gas tank. So the pressure is not building in the tank due to a loose or incorrect fitting gas cap or a loose,cracked fuel line, or bad check valve in the charcoal canister for the fuel tank vapor release line.

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Strong fuel odor coming from left front fender by air filter ,also a lot of pressure build up in tank when you remove cap kmkaren56.@bellsouth.net


If the check engine light is on, take the car to an autoparts store and have them use a scan tool to retrieve any fault codes stored in the computer. Most autopart stores offer this service at no charge. There could be a problem with the evaportative emission control system. There is a charcoal cannister that stores gas vapors and when conditions are right, a purge valve opens and the vapors are used in the combustion process. The cannister can get full of vapors and if the valve/solenoid is bad, it cannot purge itself of the vapors. Also integral to the system is the gas cap. A faulty gas cap can cause problems within this system. I am not saying that the evap system is the cause, but the pressure build up in the tank makes me suspicious. Get the codes read and it will help narrow things down for you. Sure hope this helped and best wishes.

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Check engine light code PO442


You likely won't notice any drivability problems. P0442 indicates a fuel vapor leak in the EVAP control system. It means a very small leak has been detected. In fact, the leak can be from a hole as small as 0.04" in diameter. 
The (EVAP) emission control system prevents the escape of fuel vapors from a vehicle's fuel system. Fuel vapors are routed by hoses to a charcoal canister for storage.
Later, when the engine is running a purge control valve opens allowing intake vacuum to siphon the fuel vapors into the engine.

With a P0442, the most common repair is to Remove and reinstall the gas cap, clear the codes, and drive for a day and see if the codes come back. Otherwise, replace the gas cap, or Inspect the EVAP system for cuts/holes in tubes/hoses.

Good luck and hope this helps

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I have 1990 chevy pickup 1500 4 wheel 350 eng. throttle body inj. the truck started missing and stalling i changed fuel filter and it ran good for 2 days then started the same thing so i changed fuel pump...


It sounds like the engine is pulling fuel from the tank, and not replacing it with air, causing a vacuum to build in the tank. The vacuum, may build to the point that it resists the fuel pump's efforts to **** fuel from it. If the vacuum is sufficient, it may collapse the tank, or expand the fuel enough for the engine manifold vacuum to **** raw gas into the evaporative emissions control system, hence the cannister.

Replacing the fuel pump, and filter will both break this vacuum, and make it run well for a few more miles, until the vacuum builds again.

The tank is usually vented to relieve pressure and vacuum through the gas cap.

Basically, sounds like a bad gas cap.

Try driving with the cap loose or removed. If that fixes it, buy a new cap. Preferably a locking one, as the amount of fuel these trucks hold is pretty tempting to less than honest folks. My 1990 C2500 has a 34 gallon tank.

Coil?? with the other symptoms, how'd you come up with that?

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1 Answer

1995 Nissan 300 ZX


check and see if you have a vented gas cap.the vent may not be working,maybe blocked.you may also need to check your vapor canister in the engine compartment.

Jul 11, 2008 | 1995 Nissan 300ZX

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