GMAN,
First of all the code 552 is described as "Air Management 1 [AIRB in 1993 and later terminology] circuit failure".
This air injection system is also referred to as a "thermactor"
However, I do not think it applies to you, or your SHO. Ford accomplishes cleaner exhaust emissions by using an air pump in engines larger than 4.9L (the 5.0L for example), and a "pulse air" system on the 2.3L engines.
The "pulse air" system is a reed valve system that uses the exhaust flow pulses to open the valve and draw fresh air into the exaust stream to aide in the burning of unburnt fuel and CO.
Check a service manual for your model year, but I do not remember ever seeing either of these systems on 3.0L Ford engines for the 90s model years. I do not know if these systems were used on California cars, but it is a good possibility as California is more strict about emissions.
IF I am correct, then the code does not mean anything to you. It means the computer did not get a signal from the aforementioned system. This would be logical because the system, that is air injection, is not part of your system.
The EEC IV computer ignition system is used with several engine sizes, not just your 3.0L or 3.2L SHO engine.
Let us know what you find out. This is a very interesting question, and a great learning opportunity for all of us. rangerj