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That depends who made the tune. Some tooners like to turn off things like O2 sensors so the PCM loses the ability for adaptive strategy I had a JDM 87 octane and it spark knocked its ass off with 87 octane when I put 93 it still spark knocked just not as loud. If the tune is written for 93 octane it may or may not spark knock with 91 octane because with 10% to 15% ethanol it's actually higher anyway.
You can't run any CAI other then a K&N without a tune on newer Fords it will cause them to go to limp mode. L/Ts will cause the same thing because of the movement of the O2 position and high flow cats don't scrub as well as stock cats. My rear O2 still work and I have high flow cats and the truck still has the ability to run E85 and adaptive strategy but then again my tuner has over 18 years of experience and most of it is F-150s.
That is either laziness or inexperience or a combination of both on the tooners part. Your truck can run both 87 and 91+ from Ford there is really no reason to disable that ability. What this tells me is the tuner is turning off the O2 sensor and the knock sensor why they would do that on a simple CAI L/T setup is beyond me. My tuner IIRC doesn't do an 87 octane tune he does a bad gas tune which basically the same thing.
Sorry I should have worded that better Roush, K&N, and a few other don't require a retune but most do. The 04+ F-150 has the thing like the Mustang if the MAF sensor is not in the 150% same position it will but it to limp mode. I know JLT requires a retune and I believe Airaid and AFE also do.
