Lack of Vapor from Gas cap + P1457 + P0171: Likely suspects?

Symptoms on my 99 Acura Integra LS Auto:
When I open the gas cap, not much vapor is trying to escape anymore (lack of the usual sound)
P1457 → EVAP Control Sys Leak (Canister side)
High LTFT could throw P0171

From the shop’s last diagnosis, purge solenoid is not the culprit. I tried different gas caps but no luck. Smoke test seems difficult as it might be under the car.
This video explains it well – but my Vent valve is different than the one in this video:
<https://www.youtube.com/watch?v=ad8zvUA10og&gt;

Link to my Vent Valve – it seems mostly plastic except the base hence little change for leaks:
<https://www.amazon.com/Genuine-Honda-17310-SV4-L32-Canister-Valve/dp/B00KTL7QY8&gt;

Any thoughts, pointers?

The video also has a diagram with Green line dividing P1456 vs 1457. This coupled with different Vent shut valve makes troubleshooting tricky (besides, I do not have the expensive scanner that is being used).

What could cause lack of vapor in the gas tank? How is it escaping and making engine to think more air or lack of gas?
The vent valve is normally open. Why would PCM closes it?
In my car, Vent valve connects to the Purge Valve. Outside air connection is likely from the Canister itself (not from the Vent Shut valve).

Would a failing Vent valve brings more air into the system? Perhaps it sends more air into the manifold via Purge Valve?

• This topic was modified 2 years, 4 months ago by  .

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