Honda Evap

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  • glen
    Junior Member
    • Nov 2007
    • 17

    Honda Evap

    Ok this is a 04 civic with a 1.7,Vin # 1HGEM22564L010133. It has been to a couple shops and the dealer before landing here. The car originally had codes P1156 and P0497. The fuel cap, purge valve, canister shut valve, bypass valve and charcoal canister were replaced. When it came to me P0497 has returned. I’m using the verus with 11.2 so I can run the evap system test. In two minutes with bypass and csv on and the purge running at 19.99% it pulls the tank pressure reading from 2.53v to 1.9v. This is with a half tank of fuel. After it runs the test the scanner says loose cap, cvs open ,large leak or disconnected line between 2wbs and fuel tank. 2wbs is referring to bypass valve im assuming. Anyways I have repaired these evap systems before and the shut valve is usually the problem and when I run this test on a properly working system it pulls the pressure sensor down to 1.5v pretty quickly, so the problem is there. Heres what ive done. Checked purge line from valve to tank and no restrictions. There is strong vacuum to purge valve. When running purge at 19.99% it is creating a strong vacuum from it. Smoke tested system, the system equalizes pressure, removed rear seat and fuel pump access cover no visible smoke from pump seal. You can see mostly everything in this evap system and no visible smoke. I ran evap test with filler neck blocked off- same results. I made sure fresh air tube for psi sensor was not blocked. I used a vacuum pump on the psi sensor and it held vacuum and is capable of reading through its voltage spectrum. All of the valves can be commanded on and off so no drivers were taken out. Not sure if anyone knows if theres a calibration out there for this car I called my local Honda dealer and they said no, but they can be wrong . Has anyone seen a tough to find leak on these cars? Any help or input would be appreciated, thank you!
  • SnapOnKid
    Senior Member
    • Jan 2011
    • 870

    #2
    Originally posted by glen
    Ok this is a 04 civic with a 1.7,Vin # 1HGEM22564L010133. It has been to a couple shops and the dealer before landing here. The car originally had codes P1156 and P0497. The fuel cap, purge valve, canister shut valve, bypass valve and charcoal canister were replaced. When it came to me P0497 has returned. I’m using the verus with 11.2 so I can run the evap system test. In two minutes with bypass and csv on and the purge running at 19.99% it pulls the tank pressure reading from 2.53v to 1.9v. This is with a half tank of fuel. After it runs the test the scanner says loose cap, cvs open ,large leak or disconnected line between 2wbs and fuel tank. 2wbs is referring to bypass valve im assuming. Anyways I have repaired these evap systems before and the shut valve is usually the problem and when I run this test on a properly working system it pulls the pressure sensor down to 1.5v pretty quickly, so the problem is there. Heres what ive done. Checked purge line from valve to tank and no restrictions. There is strong vacuum to purge valve. When running purge at 19.99% it is creating a strong vacuum from it. Smoke tested system, the system equalizes pressure, removed rear seat and fuel pump access cover no visible smoke from pump seal. You can see mostly everything in this evap system and no visible smoke. I ran evap test with filler neck blocked off- same results. I made sure fresh air tube for psi sensor was not blocked. I used a vacuum pump on the psi sensor and it held vacuum and is capable of reading through its voltage spectrum. All of the valves can be commanded on and off so no drivers were taken out. Not sure if anyone knows if theres a calibration out there for this car I called my local Honda dealer and they said no, but they can be wrong . Has anyone seen a tough to find leak on these cars? Any help or input would be appreciated, thank you!
    I bet your having a similar issue Like I had on an 04 Acura MDX turned out to be the filler neck...

    Here is a link to show what I found with pictures.

    Comment

    • glen
      Junior Member
      • Nov 2007
      • 17

      #3
      fixed

      Thanks for the reply kid but it had a different filler neck but heres the fix. The problem was the vapor pressure sensor, it would read through its entire range if you tested it with a vacuum pump and read the voltage on the scanner , but it wasn’t reading accurately and it was tough to see that because the vacuum pump reads in in/mercury and the sensor is working with mm/mercury. So with everything back together in the car I ran the function test and scoped the sensor and the voltage goes down but very slowly and the signal is not smooth as it would jump up a tenth of a volt very quickly and then continue on down. Also the tank would actually start to collapse and pull away from tank straps because the ecm keeps commanding vacuum to try and get it to come down more. So anyways after I replaced the sensor it would pull the signal voltage down to 1.5 in 25 seconds and yes I had a stop watch to compare. With the old one it took 2 mins to bring it down to about 1.9 which obviously wasn’t acceptable so it would set the code for low purge flow. I just researched and found that dwyer now makes a mm/merc gauge which I think is new because ive looked for one before, so I will have to get it because that would have helped. Hope this helps someone in the future,Maybe even put it in troubleshooter, not sure how they choose which tips get approved. Anyway on to the next one.

      Comment

      • Crusty
        Senior Member
        • Dec 2007
        • 2450

        #4
        Originally posted by glen
        Thanks for the reply kid but it had a different filler neck but heres the fix. The problem was the vapor pressure sensor, it would read through its entire range if you tested it with a vacuum pump and read the voltage on the scanner , but it wasn’t reading accurately and it was tough to see that because the vacuum pump reads in in/mercury and the sensor is working with mm/mercury. So with everything back together in the car I ran the function test and scoped the sensor and the voltage goes down but very slowly and the signal is not smooth as it would jump up a tenth of a volt very quickly and then continue on down. Also the tank would actually start to collapse and pull away from tank straps because the ecm keeps commanding vacuum to try and get it to come down more. So anyways after I replaced the sensor it would pull the signal voltage down to 1.5 in 25 seconds and yes I had a stop watch to compare. With the old one it took 2 mins to bring it down to about 1.9 which obviously wasn’t acceptable so it would set the code for low purge flow. I just researched and found that dwyer now makes a mm/merc gauge which I think is new because ive looked for one before, so I will have to get it because that would have helped. Hope this helps someone in the future,Maybe even put it in troubleshooter, not sure how they choose which tips get approved. Anyway on to the next one.
        Here's one for the programmers to take note of. The SCALE the vehicle uses and in the service manual can be CRITICAL to proper diagnosis. When we plug in our scan tool to whatever make of vehicle, the scanner should display the SAME SCALE AS THE VEHICLE so we don't have to take a calculator and a conversion chart along with us to the vehicle.
        Good work to persevere through the different tools and the different scales and isolate the root cause of the problem.

        Comment

        • glen
          Junior Member
          • Nov 2007
          • 17

          #5
          Thanks, i agree that the correct units should be used, they could even make it like choosing between u.s. and metric units in the scan tool set up so you could use what your comfortable with. Also during the system test the info is not written in the standard pid format, but if it was i could graph the psi sensor and have some time comparsions to watch instead of the stopwatch.It is a nice test feature to have for honda though.

          Comment

          • SnapOnKid
            Senior Member
            • Jan 2011
            • 870

            #6
            Thanks for the follow up Glen!

            Comment

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