I've been through this recently. My ECU burned out last summer and I decided to get a brand new one from Ford. They gave me the wrong one, though. The symptom was that it wouldn't return codes. I decided to purchase a used A9L from Mustang Parts Specialties, installed it and it started reading codes. My Mustang runs great now after sitting since last May.
I would start by installing it and running the KOEO test to see if you get codes back. If you do, start it up and see how it runs.
The dealer I went to said that they have no way to test the computer.
The sticker over the back port is the service port. They use that at the factory.
|