Eec Iv Fi Control System

You're right, no knock sensors with our vintage. A road course car could go lean due to fuel delivery problems, so it's possible it wasn't the fault of the tune. Or it's possible that it was. Only one way to find out, and you already have that anwer.

There are a number of tables in the tune that dictate the spark advance at any time - based on temperature, load, altitude, etc. And modifiers (percentage and discrete) that further modify the spark. To some degree there's always uncertainty - based on quality of gas, fuel delivery issues, etc. A 'safe' tune retards the timing enough to keep the engine safe while leaving power on the table. That's just the way it is - with no knock sensors.

The EEC-IV tunes have some knock-sensor capabilities built in. I've read however that the board has no hardware components to actually support it, and know no one who has ever done so. You could run an aftermarket system like MSD if you wanted that extra-cost extra-feature. Leaves less power on the table while still being safe for the car, of course at a cost.