I can see your point to a degree... But it does not make sense that it ran so poorly. A little hesitation here and there, sure. But it was barely making it up hills. Keeping in mind, that I probably need new spark plugs and that it may enhance the "compression issue" to a point that it runs rough, I even believe that it could be the culprit. But in no way will I believe that with a perfectly running engine 93 octane will make it run worse all by itself.
So theoretically, if I were to tune the timing and injector pulse to compensate for the need for added compression, I could actually save fuel?
yes, bad spark plugs could definitely make it worse. it is kind of like, when one little thing goes wrong, you wont really notice it, but when lots of little things start happening, that all adds up.
but, i can tell you from personal experience, that a perfectly running engine will run noticeably rougher on 93 when 87 is recommended. I experienced it first hand, borrowing my dads 1 year old F150 helping a friend move. I had to throw in a few gallons of premium because at 2 in the morning, the little middle of no where gas station was out of 87. this is actually what caused me to start researching the 87 vs 93 octane thing in the first place, because all those years ago, it made no sense to me that a different octane would cause that.
now as for tuning your montero to run on 93. I am not sure exactly how you would, or why. i run 87 in my LS and I am perfectly happy with the way it runs and have no desire to tune it other wise.
