I have had a small EVAP leak ?

2020 FORD F-250
95,000 MILES • 7.3L • V8 • 4WD • AUTOMATIC
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CAJUNSUPERDUTY
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I have had a small EVAP leak that I diagnoses to a fitting on top of the tank. I had to put in a new tank. I thought the problem was fixed but now I’m getting a large leak code. I have been trying to diagnose by doing a smoke/pressure test. I cannot find a leak anywhere and am starting to suspect maybe the FTPS is the problem. My big problem is finding the literature to point out component locations. I believe the FTPS is on top of the tank maybe connected to the fuel pump but I’d have to drop the tank again to verify. I need some help troubleshooting this problem!

While I have been able to close the vent valve and open and close the purge valve to seal the system, there appears to be a “vapor block valve”? That I cannot find and can’t find literature to show it or explain what it is. I need help from someone who has access to this specific vehicle.
Mar 23, 2026 at 3:31 AM
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STRAILER
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Can you please give us the codes number? A small leak turning into a large leak right after tank work usually points more toward a hose connection, seal, quick-connect, lock ring seal, vent line, or top of tank plumbing issue than a bad FTPS. Also, I have seen the fuel pump module tank sealing O ring have an issue and not seal correctly. I would do a smoke test by following this video to see where the leak is coming from before I did anything.

https://www.youtube.com/watch?v=aTNr3IEgVF0

Please upload a short video in your response of the problem, so I can see what's going on
Mar 23, 2026 at 5:05 PM
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CAJUNSUPERDUTY
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The code is P0455. I wish my problem was a simple as this video!
I have a good smoke machine that puts out a lot of smoke. I’ve sent smoke through the filler neck, the vent line, and the purge valve, I’ve controlled the vent valve and purge valve and I cannot find a leak anywhere.

I would suspect something to be leaking after swapping out the tank also but I’m not seeing anything anyhwere. That’s why I’m suspicion of the FTPS but also there is apparently something called a vapor block valve but I don’t have good literature that shows me where any of these parts are. I know where the purge valve is and the vent valve and what they do but that’s it.

I’m not sure what you mean by uploading a short video? Do you mean of me doing the smoke tests?
Mar 23, 2026 at 5:51 PM
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STRAILER
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P0455 means a large EVAP leak. I was hoping to see where the smoke leak was coming from but you say there is none correct? I have seen the EVAP vent valve up by the engine have a supply line leak or the valve go bad which does not allow vacuum to enter the EVAP system so it thinks there is a leak. Here is the location of the valve so you can check the O ring seals of the lines and to put 12 volts to it and make sure it opens. Also, make sure the gas cap has it O ring on it. Check out the images (below). Let us know how it goes
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Mar 24, 2026 at 9:01 AM
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CAJUNSUPERDUTY
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That’s not where the “vent valve” is, that’s where the purge valve is. You’re not really familiar with with this vehicle are you?
Mar 24, 2026 at 10:23 AM
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STRAILER
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Sorry I misspoke, yes the purge valve. Good luck with your repairs.
Mar 25, 2026 at 11:14 AM