[S550 Question] Hard Start After Refueling (2017 2.3 EcoBoost) - Codes P1450 & P0456 - Purge Valve Replaced

[CoolMonkey]

Hi everyone,

First off, apologies for dropping an S550 question in the S650 section! I have my own S650, but I'm trying to help out a good friend who is having a really frustrating issue with her 2017 and is running out of ideas. I figured some of you might have dealt with this on your previous cars before upgrading, so any insight would be hugely appreciated.

Vehicle: 2017 Ford Mustang 2.3 EcoBoost (US Spec) Error Codes: P1450 & P0456

The Symptoms: Every single time she fills up the gas tank, the first start is extremely rough. It has a hard time starting, sputters, and stumbles. She literally has to pump the gas pedal to get it going.

What we've already done/tried:

• Purge Valve: Replaced the EVAP purge valve/vapor tube assembly (Part # FR3Z-9G297-H).
• Fuel System Flush: We flushed the fuel system. After this, it started perfectly fine a few times, but then the hard start issue came right back.
• Fuel Pump: The fuel pump started making a grinding/clicking noise recently, so that was pulled and refurbished.
• Charcoal Canister: The mechanics suggested swapping out the EVAP charcoal canister (Part # JR3C-9E857-B) hoping it would solve the post-refueling issue. Unfortunately, it didn't help.
• Pressure / Leak Test: The system was fully inspected and pressure-tested. They found zero leaks anywhere. Interestingly, right after the pressure test, the car started beautifully after one fill-up, but went right back to the hard start on the second fill-up.
• Software Bypass Test: As a test, the mechanics temporarily reprogrammed the PCM to ignore the EVAP system so it wouldn't throw codes. Even with the codes bypassed, the car still had the exact same hard start after refueling. They flashed it back to the factory stock tune afterward.

It seems like we've chased down the usual EVAP suspects (purge valve, canister, vacuum leaks), but the issue is completely stubborn.

Has anyone dealt with this after already replacing the purge valve and canister? What else could be causing this vapor lock or flooding situation only after getting gas?

Thanks in advance for the help!

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[Zig]

Any update to airfilter?

 

[Zig]

By chance have you tried: “The "Under-Fill" Test: On your next trip to the gas station, only fill the tank to half-full (1/2 tank). Do not fill it until the pump clicks. If the car starts perfectly at half-tank but stalls at a full tank, it proves that liquid fuel is physically splashing into the vapor lines because the tank's internal float valve is mechanically compromised.”

 

[DarkHorsePremium]

"Only after getting gas"

So once the car is started, it runs normally, accelerates normally, etc?

What about a faulty fuel pressure sensor?

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