Hi, Ok-
I did a bit of digging & found this is the ECU for the 2004 Chassis with a strategy number for a 4.6L V-8. Not a 3.8L V-6.
Yes, this is likely your issue.
I wouldn’t worry about acquiring another computer just yet, this is obviously getting through the PATS handshake & is highly likely the stock CPU.
You can get a V-6 to run off a V-8 CPU, tuning is involved to get around issues such as you’re having, or- like the typical individual- you can buy a V-6 CPU (which I recommend against at this point). Certain CPU parameters need to be correct. First- let’s establish what the Mfg. says this pony was really bred as from the factory.
You can snap a pic of the vin plate, I’m not available tonight- but post it, and this you can also do this yourself. I fail to see why they would do a V-6 swap into a GT, but this mindset helps nothing. Moving forward....
Type the VIN # into a google search, some sites will pop up and allow you to see if the car was actually equipped with a 4.6L V-8 (Making it a GT). I’ll get back with you tomorrow, so- post a VIN # pic up, I’ll verify this for you then-k?
It’s also pretty easy to visually tell a V-6 Mustang from a V-8 by certain design(s), styling and parts under the chassis. If it’s been modified, may be more difficult for you.
It’s discussed here on Stangnet in the archives, here’s a link..
https://www.stangnet.com/mustang-forums/threads/differences-between-v6-and-v8.716798/
Ok, talk tomorrow- good luck!
-John
P.S.
Please verify I got that CPU ID right, fuzzy..
4R3A-12A650-RC PCM MPC-15C