need help with gm evap system

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  • kevin hodges
    Junior Member
    • Nov 2011
    • 3

    need help with gm evap system

    2008 GM 2500 HD 6.0 engine codep0455. changed fuel cap and vent solenoid nothing has changed code comes back. Here is my question will the evap test hold a vacuum on the system so i can look for the leak ? Or am i just nutts. Can some one give me step by step how to use this test on my scanner and what pid values should be. And also where could i find more tranning on the SolusUltra thank you
  • sbebenelli
    Member
    • May 2007
    • 46

    #2
    What test did you do that made you think it needed a fuel cap and vent solenoid? Have you smoked the system to make sure their are no leaks and all the controls are working OK?
    Last edited by sbebenelli; 03-21-2012, 06:47 PM. Reason: spelling

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    • Bob's Garage
      Senior Member
      • Nov 2007
      • 3257

      #3
      Originally posted by kevin hodges
      2008 GM 2500 HD 6.0 engine codep0455. changed fuel cap and vent solenoid nothing has changed code comes back. Here is my question will the evap test hold a vacuum on the system so i can look for the leak ? Or am i just nutts. Can some one give me step by step how to use this test on my scanner and what pid values should be. And also where could i find more tranning on the SolusUltra thank you
      For your purposes, a good evap test is the purge and seal. This test closes the vent solenoid and allows you to control the purge solenoid. I usually pull about 10 mm hg in the tank before I hit "Seal" you can then watch the vacuum decay. More than likely, you will see a rapid decay because of your P0455. Graphing the test is helpful and Ultra can do that well.

      Assuming you have access to a smoke machine, to find the leak, KOEO, use the vent solenoid functional test. Make sure your vent solenoid actually works first of course. You should hear an audible "thunk" when the vent closes. You can run the smoke machine with the vent open, so the air spaces can fill with smoke and then shut the vent solenoid and look for smoke any where. Use an air gun to blow away concentrations of smoke to see where your leak is.

      Typically, the best place to smoke from is the fuel filler neck, because there is a check valve in the fuel tank that stops smoke from entering the filler neck if you smoke it from the front. However, it is unlikely that the neck is not rusted out on a 2008 although not impossible. So, if you have no adapter for the filler neck for a smoke machine, you will have to smoke it from the front.

      Most likely a hose is off at the canister or the purge. BTW, make sure the purge valve is not leaking vacuum when the command is 0%, this is an often overlooked source for evap leaks.

      Here is a number to remember. KOEO, gas cap off, the FTP sensor should be between 1.3 to 1.7 volts. It usually rests at 1.5 volts.

      Good luck, we'll check back later,

      Bob

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      • Trindaddy
        Senior Member
        • Jan 2010
        • 339

        #4
        Hi Kevin. I like Bob's advise and would like to add my help. First, this post should probably be in the evap forum that way others can find it and you may even attract the attention of a couple of big time evap gurus that i know frequent that forum.

        Anyway, i have found a few GM cars that do block flow up the filller tube. i suggest you test from the front first. Seal the vent using scanner. If you find a leak, fix or block it and test again. If you don't have smoke and you see the flow-meter dwindling, switch over to "test" mode on the smoke tester as it is much more accurate at indicating amount/size of leak (if any). If meter falls to bottom indicating you have no more leak then remove the gas cap. If flow shoots up then you have indeed tested to the cap without disturbing it. If you remove the cap and the flow doesn't change then you need to test by connecting to the neck. Do it this way every time and you'll never get burned and you won't disturb the "loose/improperly installed cap" clue.

        I have seen on these newer GM trucks and cars, an unusual amount of leaking purge valves. They usually set "flow detected during non-purge" codes. Vent valves are the classic GM truck leak spots. Run the "test" mode on evap tester while opening and closing vent valve numerous times. Beware: because the system usually operates using vacuum, introducing pressure then trying to open and close the vent will often make it "stick" closed. Release the pressure in between tests to avoid mis-diagnosis.

        Scan through the "Evap forum" here for lots of great advise. Your in the right place. Folks here are great. Good luck.

        Neil

        Comment

        • dave-m
          Member
          • Feb 2011
          • 54

          #5
          Had three different vehicles this week with P0455 code.

          First was a 2008 Mazdaspeed 3, poor coverage on this vehicle with Snap-On Scanner, no functional tests for EVAP. Checked for TSB's, found several for the EVAP system. Checked the Purge Solenoid and it was stuck open, common failure. Replaced with an updated part from Mazda.

          Second was a 2007 GMC Denali 6.2L. Cleared codes and checked the Vent and Purge Solenoids for proper operation, seemed OK. Hooked up the smoker and triggered the Vent Solenoid, worked fine with no leaks. Opened the Vent Solenoid and no response, Solenoid would stick with any pressure in the system. Replaced the Vent Solenoid to correct this problem. Rechecked the system only to find the Purge Valve was also stuck open. Used the Scanner to close the valve, had a vacuum gauge hooked to the Evap Canister side of the Purge Solenoid, gauge showed vacuum with valve closed. Replaced Purge Valve and everything OK.

          Final vehicle was a 2008 Silverado 2500 HD 6.0L. Repeated the above steps. This time Vent Solenoid functioned normally at all conditions. The Purge Solenoid Valve was stuck open. Replaced it and system ok.

          Comment

          • Crusty
            Senior Member
            • Dec 2007
            • 2450

            #6
            Just to follow up on Bob's advice, the fuel tank pressure VOLTs should be very close to 1.5-volts at atmospheric pressure (no pressure or vacuum on the system)
            From 1.5-V down to 0.1-V it indicates a pressure
            From 1.5-V UP to aproximately 4.0-V indicates a vacuum.

            BTW, if your service manual spec tells you to look for a certain amount of Inches-of-Water-Column (inH2O), take the mmHG your scanner shows and multiply that mmHG value by 0.5353 to get inH2O.....
            (I shouldn't know that but what the heck.....)

            Here's a couple of screen shots from a Solus-Pro and a Solus-Ultra showing a propelry functioning EVAP system (2001 M/Y)
            Attached Files

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