Evap problems

Well this is my deal!
My 2004 xlt 4.6l OBDII ready test the evap system won’t make it three the test.the computer is telling me that it cant build up any vacuum.So I start with a new purge solenoid.it wasn’t work, I tested it and it was bad.so replaced that. Still had same problem.
So get get to reading everything out there about the evap system and come to the conclusion that it must be the FTP(fuel tank pressure sensor)
So I look for one of those,witch for some reason ever body I talk to about getting one tell me that my FTP is fitted in the gas tank.but mine is in a Hose that runs up to the filler neck.so very long story short I had to get one for a crown Vic.so I do that by the way it was 140.00 bucks couldn’t believe that!so I put it in and still have the same problem.so I run FORScan and find out it’s reading the same as the old one and never changes.so here my ? For you all! Could there be a problem with myPCM and that’s why the new one and two other one all read the same.and when I unplug them the voltage will change . So I know the wires are ok.
Need your guys help with this!!!!!

For all the $$ and time you have spent, you could have a smoke tester (Hamfisted said: Smoke tester, so you can see what line(s) are actually leaking : https://www.amazon.com/AutoLine-Pro...tive&sprefix=smoke+test,automotive,196&sr=1-4)
and maybe find your problem w/o throwing parts at it. You have a 16 year old machine with deteriorating rubber lines in it that leak & crack from heat and age, begging to be replaced.

Oh I’ve done that.
What Iam saying is can it be the pcm that is cause the bad reading.
I have no links.