99 Legacy SUS (2.5)
I have been experiencing a dip in mileage and have taken care of Plugs, wires, etc...
Heard that the ONLY O2 sensor that affects your mileage and performance is the Pre-cat (3-wire). However, a parts person at a Sub. dealership said that both are of equal importance. However, I can unplug the post-cat and no CEL is thrown???
Basically, I need the straight poop on O2 sensors. FACT not OPINION please. It seems strange that the post cat (4-wire) would cost 2-3 times more, but not have any affect on performance. TIA.
Also, could a universal 3 wire be adapted to the 4 wire? I know you'd lose a lead (Most likely the ground) but don't know if that would cause problems, or if the loss of the negative rail is inconsequential as this is DC not AC power.