[Blue Bowtie]

Your 1983 CARBURETED engine does not have a fuel cutoff MPH parameter which does anything. The ECM has no control over fuel delivery to the carburetor, and only operates the MC solenoid and affects the ignition advance. Later (about 1984) ECMs controlling CFI, TBI, TPI, and SFI engines used speed limiters to cut off injector pulses anywhere from 98 MPH on some truck to 118 MPH on a lot of passenger cars to 254 MPH on others. Some trucks were limited to 94 MPH for safety, and most passenger cars were limited depending upon the speed rating of the tires originally shipped with the vehicle. Since several cars had "Z" rated tires from the factory, the fuel cutoff parameter was usually set to the maximum value of 254. Obviously, none of them could attain anything near that speed and were considered "drag limited" vehicles due to aerodynamic pressure.

You can load up a free editor such as TunerPro, load the correct mask (TDF) file, then read the binary (BIN) file for your vehicle to see if I am misleading you.