How can I force open loop using tunercat? Is there a way to do this without throwing an SES (ie unplugging the maf).

Is running the car in speed density the same as open loop? (I would imagine SD still uses the O2's?)

 

Closed loop and speed density are two different things. Speed density does not use the MAF to determine the amount of air entering the engine, it instead uses the MAP and IAT. This is what the 93 LT1 cars use.

You can force the PCM to stay in open loop by going to the ECM constants and setting the Min Cool Temp for Closed Loop and Min Cool Temp for Closed Loop, Cold MAT to the highest possible temperature. This will effectively disable closed loop because the temperature will never reach that high to go into closed loop.