Evap system vapor pressure - engine light 💡
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Evap system vapor pressure - engine light 💡
I have a recurring evap leak for codes 0451 and 0455.
i took freeze frames of my data and it’s showing evap system vapor pressure as 14.70 in h20.
from what I read anything over a positive value of about 5 is a problem. I’ve already replaced purge valve which I did diagnose as bad with finger test but I’m still getting the code and engine light.
is this vapor pressure indicative of a particular problem? I’m wondering if the vent valve on the canister is stuck closed and has therefore allowed a buildup of positive pressure in the tank and evap system. But I’m not sure if I’m interpreting that correctly.
I tried to attach screenshots of my scan but I’m having trouble attaching them with my phone.
i took freeze frames of my data and it’s showing evap system vapor pressure as 14.70 in h20.
from what I read anything over a positive value of about 5 is a problem. I’ve already replaced purge valve which I did diagnose as bad with finger test but I’m still getting the code and engine light.
is this vapor pressure indicative of a particular problem? I’m wondering if the vent valve on the canister is stuck closed and has therefore allowed a buildup of positive pressure in the tank and evap system. But I’m not sure if I’m interpreting that correctly.
I tried to attach screenshots of my scan but I’m having trouble attaching them with my phone.
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https://www.motor.com/magazine-summa...ation-testing/
I also found this which has a wealth of info. Which makes me think the system isn’t able to draw any appreciable vacuum and triggering the large leak code. Maybe that just doesn’t get captured in the freeze frame.
I also found this which has a wealth of info. Which makes me think the system isn’t able to draw any appreciable vacuum and triggering the large leak code. Maybe that just doesn’t get captured in the freeze frame.
Last edited by Linus Bicker; Dec 4, 2018 at 08:07 PM. Reason: Forgot link
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From: St Louis
First thing to do is verify that the FTP sensor is reading zero when the tank is at atmospheric pressure. Pull up that PID on your scan tool and monitor it with the fuel cap off (or fueling adapter is installed, if capless) and verify 0" H2O pressure. Too much offset would indicate a failed FTP sensor which could account for both of your DTCs.
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First thing to do is verify that the FTP sensor is reading zero when the tank is at atmospheric pressure. Pull up that PID on your scan tool and monitor it with the fuel cap off (or fueling adapter is installed, if capless) and verify 0" H2O pressure. Too much offset would indicate a failed FTP sensor which could account for both of your DTCs.
its no where near zero on either vehicle with engine off or with it running. Bounces around from positive to negative pressure like tennis ball. I wish I could attach the screen shots.
Lookimg at it again I see that my truck the pressure is almost a constant 8000 with frequent spikes downward into negative pressure. The mustang is more of a steady pattern of giant ups and downs.
the app measures it as PA
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Roadhog123
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