which would consume more fuel?

[cg111]

Hey all, first post here.

Been doing some research about fuel efficient driving lately and got conflicting results.

first of all, my car is a 1995 nissan sentra 1.6 M/T. Interesting to note though, it doesnt have an o2 sensor, no catalytic converter, egr, and evaporative emissions control.

now to the question(s), is it more efficient to shift at lower vs higher rpms? (2000 vs 3000) after watching the youtube video of engineering explained about shifting for the best fuel economy, where he said its more efficient if the engine is loaded and at a low rpm. and its more efficient to accelerate on a higher gear (lower gear ratio) than a lower gear (higher gear ratio). but some say the exact opposite... its more efficient to accelerate at a lower gear as you are stepping on the throttle less and the injector whatever time is also less...

if i step on the throttle more at a low rpm to accelerate (engineering explained method), the engine will be loaded more. wouldnt the ecu retard the timing and inject more fuel as the load is higher? would less pumping losses negate that effect?

what if i downshift so my rpms are higher but im stepping on the throttle less (some other guy in the internet method)? the ecu would advance the timing, and (as they say) the injector time is less. therefore better fuel economy. would higher pumping losses negate that effect?

the user manual of my car says to shift at 2500 rpm. lets say im at second gear and at 1800 rpm. not accelerating, just keeping up with traffic in front. should i hold it at second till it reaches at 2500 or shift to third? if i shift to third, my rpm will be at 1200 and i suddenly need to accelerate. would it be more efficient to accelerate from 1200 rpm, or downshift back to second?

sorry if its all confusing or jumbled up, i didnt know how i would write my questions or where to start.

any input appreciated, thanks.