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[jtgh]

EFIEs , that being what.
ahhh, youtube, how'd I guess that.

that's right up my alley ! Grin !

this works ! , the front oxy is the major fine tuning device. ( for some )

on many early 96 + cars this can work.
(results can very , read more)

the car starts, if the ECU enters closed loop ,the front sensor measures oxygen and thus the AFR ratio is set by this device output.
so his presention is real, and in fact I know it to work, both in theory and in practice.

the newer cars might not let you go too lean with out setting a code
and the newer cars might fail the cat performance monitors, P0421 in one case.

this is LEAN BURN technology.
of course do not get caught it is illegal.
What will happen ?( i run this technology in a foreign country , South America.

I run a car with lean burn at my winter home. gas is $8.00 , there. ouch.
I use a megasquirt custom ECU , far batter way to do this and I can run Ethanol.

bad sides:
1: the cat metals inside will be destroyed, in a few 1000 miles.
2: the above fact may clog it up. varies by car and year. greatly.
3: the above will cause P0421 (lazy cat fail) just wait a while.
4: remove it before smog check ,
5. remove it or you mech will refuse to work on your car (heavy fines for him)

on the early OBD2 cars, 96,97 or so you may not get lazy cat fail.
on 99 and newer, fur sure, because you killed the cat.

this technology is not magic it is used on every Prius , the engine runs in lean burn but has a very expensive , different technolgy CATCON that is immune to over heat.

so the answer is , this device will not do anything any useful for the rear OXY SEN.

the rear sensors is ONLY for monitoring the CAT performance.