Gas Tank pressure
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Thread: Gas Tank pressure

  1. #1
    Registered User rajdeep_m's Avatar
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    Question Gas Tank pressure

    Does the gas tank do the "wooshing" sound when the gas cap is opened. My 00 Ody does not(would that mean that the Gas tank does not hold the pressure or there may be a minute leak in it), though my 96 Accord does it!

    Also the check engine lite is on with code P1456(Evap. issue). Would the above problem be related?

    Thanx!
    2000 Ody EX, Navigation 145K+
    1996 Accord LX 135K+
    1992 Kawasaki zx1100 20K+
    Mobil 1 Extended Performance
    Mobil 1 ATF
    Shell V power

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  3. #2
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    Good evening,
    My 2001 LX, does the WOOOSHHHIINNNNG sound, whenever I open it.

    Good luck.

  4. #3
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    Re: Gas Tank pressure

    Originally posted by rajdeep_m
    Does the gas tank do the "wooshing" sound when the gas cap is opened. My 00 Ody does not(would that mean that the Gas tank does not hold the pressure or there may be a minute leak in it), though my 96 Accord does it!

    Also the check engine lite is on with code P1456(Evap. issue). Would the above problem be related?

    Thanx!
    Generally it will "whoosh" as it get's slightly pressurized by the (excess) fuel being returned from the engine because it is warm. This can be affected by ambient temperature also. The fuel tank is intended to be vapor tight so as to prevent evaporative emissions. It sounds like you may not be putting your gas cap on tight enough? Make sure you tighten it enough to get a few "clicks" out of the ratchet mechanism. If you are already doing this then perhaps you have a bad gasket on the cap?

  5. #4
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    A quote from my 1st thread here..

    " In 1996 the government mandated a law that wanted auto manufacturers to build "greener", cleaner cars.. one part of that process was to contain/store/re-burn gasoline fumes within your fuel tank so that they do not release hazardous fumes into our atmosphere...

    What the code P1456,P1457 means is that your car leaking or losing fuel tank vacuum when the ECU (computer of the car) is doing a self test on the evaporative emissions system.. that vacuum is the same "hissing" noise you hear when you unscrew the fuel cap to fill up the tank.. atmospheric pressure is lower inside the tank than the "outside" atmosphere, thus sucking outside air into the tank to prevent fumes from leaking out..

    Does this mean it will damage the motor? affect driveability? leave you stranded?... simply no."

    Now if you do not hear the "hissing" noise and do not have a "check engine lamp" illuminated then I would not be concerned about the issue, alot of variables involved here and the lamp would be illuminated if there was a failure in the system.
    I'm not really a Honda Tech... I just play one on this forum..

  6. #5
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    Originally posted by BreakStuff
    A quote from my 1st thread here..

    " In 1996 the government mandated a law that wanted auto manufacturers to build "greener", cleaner cars.. one part of that process was to contain/store/re-burn gasoline fumes within your fuel tank so that they do not release hazardous fumes into our atmosphere...

    What the code P1456,P1457 means is that your car leaking or losing fuel tank vacuum when the ECU (computer of the car) is doing a self test on the evaporative emissions system.. that vacuum is the same "hissing" noise you hear when you unscrew the fuel cap to fill up the tank.. atmospheric pressure is lower inside the tank than the "outside" atmosphere, thus sucking outside air into the tank to prevent fumes from leaking out..

    Does this mean it will damage the motor? affect driveability? leave you stranded?... simply no."

    Now if you do not hear the "hissing" noise and do not have a "check engine lamp" illuminated then I would not be concerned about the issue, alot of variables involved here and the lamp would be illuminated if there was a failure in the system.
    Hi BreakStuff. I'm not challenging your knowledge but have a question about what you said.

    Are you sure about the tank being under vacuum relative to the atmosphere? Evaporative emissions are caused because the fuel wants to evaporate and thus raises the pressure within the tank. My understanding has always been that as this occurs, a properly operating system stores the vapor in the charcoal cannister and then, after the engine warms up, the purge valve opens and allows the stored vapors to be drawn into the intake manifold to clear out the cannister. I believe that the current systems test for proper sealing by using intake vacuum to apply a vacuum to the tank, lines etc and then set a trouble code if this test fails, but that the tank does not generally operate under a vacuum. I seems perfectly logical that a vacuum test rather than a pressure test is performed as there is a built in source of vacuum with the intake manifold but not a built in source of pressure.

    I guess this is all somewhat esoteric but I want to make sure I'm understanding the system and your comments properly. In any event, if rajdeep_m has the evap system trouble code, it may not cause an operational problem but I believe it does mean that excessive evaporative emissions are probably taking place and that he/she may not pass an emissions test. Do you agree?

    Thanks!

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    Sorry my bad mejmea,

    My answer is bad because I didn't realize that rajdeep had the check engine lamp illuminated.

    Is the non-existent "hissing" noise is related to the P01457/P01456 code?. Yes, its most likely related.

    "Are you sure about the tank being under vacuum relative to the atmosphere? Evaporative emissions are caused because the fuel wants to evaporate and thus raises the pressure within the tank.

    Thats some good stuff mejmea,

    You are absolutely correct with your understanding of the evap system.

    Its not so much a problem of the fuel evaporating as it is with the fuel "sloshing" around while driving. Thats the + pressure created that needs to "recycled" back into the intake system for combustion and to avoid entering into the atmosphere.

    Alot of variables involved here such as fuel tank volume,temperature,pressure (in relation to atmospheric pressure) for the ecu to determine optimal combustion and to keep the EPA happy.
    Different geographical locations can produce different results. But you have the correct understanding.
    Last edited by BreakStuff; 01-20-2005 at 10:12 PM.
    I'm not really a Honda Tech... I just play one on this forum..

  8. #7
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    Ok, thanks Breakstuff!

  9. #8
    Registered User rajdeep_m's Avatar
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    Smile

    Thank you Guys, you all have been very helpful.

  10. #9
    Registered User rajdeep_m's Avatar
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    Lightbulb

    Would this issue(P1456) get my Gas mileage down? I am getting around 16 mpg mixed driving(I am a cool customer, no rabbit driving).

    Thanx!

  11. #10
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    Originally posted by rajdeep_m
    Would this issue(P1456) get my Gas mileage down? I am getting around 16 mpg mixed driving(I am a cool customer, no rabbit driving).

    Thanx!
    BreakStuff or EricD (a Honda Service Manager) may be able to answer more specifically for a Honda but from a general engineering point of view:

    1) Is this mileage (16mpg) significantly different than what you were getting previously?

    2) It's possible that a trouble code could put the engine, transmission, etc control systems into a mode where it is not using the normal mapping schemes and thus could be less efficient but I'd be surprised if it caused a big difference in fuel economy.

    I assume that you checked to make sure your gas cap was tight. If it was my vehicle and I'd tried the simple things to no avail, I'd get it checked out at a garage that can do some troubleshooting. I believe that emissions components must be warrantied for much longer than the standard vehicle warranty (perhaps even as high as 100,000 miles, I can't quite remember) so it may not end up costing you anything. Check the simple stuff first though.

    Let us know what you find out.

  12. #11
    Registered User pvandegriff's Avatar
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    I have no gas tank pressure with NO CEL.
    I don't get any error codes but I don't get any pressure release from my gas tank for several months.

    Any idea what might be causing this?
    Don't say it's the cold weather, either. My Maxima does it every time.

    My Ody has 40k miles on it. I've checked the cap seal and all of the obvious EVAP hoses and lines under the hood.
    2000 Odyssey LX - Sold it a 91,900 miles with Gator A/T and last tank got 15 mpg city due to 82C thermostat and Bosch O2 Sensor. I'm NOT gonna miss that truck-riding pig ass design flawed shoe box on wheels.

  13. #12
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    This info is from the manual. It explains what the system checks and also tells what conditions must be met to make the light come on. In my experience the Two Way Bypass Solenoid Valve and the 2 way valve have been the culprits. Heres the info.

    General Description
    The evaporative emission (EVAP) control system stores fuel vapor from the fuel tank in the EVAP canister temporarily to prevent
    it from escaping to the atmosphere and to enable it to be drawn into the engine by intake manifold vacuum and burned.
    In addition, the onboard refueling vapor recovery system (ORVR) stores fuel vapor generated when fueling in the EVAP canister.
    The EVAP control system leak detection method improves the accuracy and frequency of the detection by determining faulty
    components and vapor leakage for each part. The EVAP control system (from the purge valve to the fuel tank) is divided into
    two parts. One is the "EVAP Canister Side" (from the EVAP two way valve to the purge valve), and the other is the "Tank
    Side" (from the EVAP two way valve to the fuel tank). Each side uses different detection principles and methods.
    The tank side 0.04 inch leak detection procedures have been modified since the ‘98 model year, and the same detection
    method is used in the first drive cycle and the second drive cycle.
    • Three steps are performed for leak detection during a valid drive cycle.
    Step 1: Start the engine from the specified engine coolant and intake air temperature. Compare the output value from the fuel
    tank pressure sensor right after start-up with the one after 20 seconds have elapsed. If there is a change between
    them, the tank side is considered free of leaks. Otherwise, go to Step 2.
    Step 2: Monitor the changes of absolute pressure in the fuel tank for a specified time period after starting the engine. If it
    changes by a specified value toward negative pressure, or the difference between the maximum and minimum absolute
    pressure in the fuel tank is large, it is interpreted as no leakage in the tank side and the detection is complete.
    Otherwise, go to Step 3.
    Step 3: If the difference between the absolute pressures in the fuel tank right after the specified time period has elapsed and
    after a while is small, it is interpreted as leakage in the “Tank Side”. If it is in the first drive cycle, a temporary DTC is
    stored. If it is in the second drive cycle, a DTC is stored, the MIL illuminates, and the detection is complete.


    Malfunction Threshold
    All of these conditions must be met.
    Step 1: The change of fuel tank pressure is 0.2 kPa (1 mmHg, 0.07 in.Hg) or less.
    Step 2: The change of fuel tank pressure is 0.2 kPa (1 mmHg, 0.07 in.Hg) or less. Or the difference between maximum and
    minimum value is 0.7 kPa (5 mmHg, 0.2 in.Hg) - 3 kPa (22 mmHg, 0.8 in.Hg).***
    Step 3: The change of fuel tank pressure is 0.8 kPa (6 mmHg, 0.3 in.Hg) - 0.9 kPa (6 mmHg, 0.2 in.Hg).****
    *** : Depending on initial engine coolant temperature and elapsed time period.
    **** : Depending on initial engine coolant temperature.

    Driving Pattern
    1. Start the engine at an engine coolant temperature and intake air temperature as specified under Enable Conditions, and
    let it idle until the radiator fan comes on.
    2. Drive the vehicle immediately at a speed between 25 - 75 mph (40 - 120 km/h) at least 6 miles (10 km).
    • If you have difficulty duplicating the DTC, retest after turning off electrical components such as the audio system and A/C,
    and try a different gear position.
    • Drive the vehicle in this manner only if the traffic regulations and ambient conditions allow.

    I don't believe the 1456 or the 1457 code will cause a loss of fuel econ. These happen after the fuel burn proccess so I makes sense to me it should not effect fuel econ. But I have done no real research into this.
    Eric

  14. #13
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    Originally posted by pvandegriff
    I have no gas tank pressure with NO CEL.
    I don't get any error codes but I don't get any pressure release from my gas tank for several months.

    Any idea what might be causing this?
    Don't say it's the cold weather, either. My Maxima does it every time.
    Its not a good idea to compare the Maxima to the Honda, or even a Honda to a similiar Honda unless the comparison parameters are equal.

    Such as,

    same size fuel tank.
    same amount of fuel.
    same evap system.
    same temperature.
    same atmospheric pressure.
    same amount of "fuel slosh" etc,etc..

    Its a pretty tight system and I wouldn't worry too much if I didn't hear the "hissing" noise while re-fueling and/or the "Check Engine Lamp" (CEL) illuminated.
    I'm not really a Honda Tech... I just play one on this forum..

  15. #14
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    EricD wrote:

    "This info is from the manual. It explains what the system checks and also tells what conditions must be met to make the light come on. In my experience the Two Way Bypass Solenoid Valve and the 2 way valve have been the culprits. Heres the info..........."

    Both the 1456 & 1457 codes as I understand it are for the evap. emissions area, BUT, is there a diagnostic difference between the two codes? Does one indicated a problem on the tank side '1456' and the other the 'evap canister side '1457' or is there no rhyme or reason as to which of the two codes come up?

    I have the 1457 and the fuel tank did get overflowed back in January.
    would that clear itself, I have cleared the code a number of times only to have it reapear often within 20 miles. Trying to figure out what to try to fix. Just did the EGR carbon drill out and was successful, no more 0401 or 0420, but the 1457 is still with me.

  16. #15
    Registered User pvandegriff's Avatar
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    Originally posted by BreakStuff
    Its not a good idea to compare the Maxima to the Honda, or even a Honda to a similiar Honda unless the comparison parameters are equal.
    I was only making the comparison to say that the COLD ARSE temperatures weren't the cause of the lack of pressure.
    I knew that as soon as I posted there would be some joker out there with the opinion that since it's January in Chicago and below freezing most of the time that must be the reason for "no pressure". Something like, "gasoline doesn't actually evaporate in temperatures below 32 degrees."

    However, the more likely reason for not hearing the "hiss" is just as you described....that I just "didn't hear it".

    I opened the cap in my garage today and there IS pressure. So, you must have been right! These damned old ears just AIN'T what they used to be
    2000 Odyssey LX - Sold it a 91,900 miles with Gator A/T and last tank got 15 mpg city due to 82C thermostat and Bosch O2 Sensor. I'm NOT gonna miss that truck-riding pig ass design flawed shoe box on wheels.

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