i know that avg milage for a 1st gen b16 w/ y1 tranny is around 25 city/ 30 hwy, cause i had one, and that's what i usually got. but, i recently bought a 91 si hatch w/ b16 swap and it was getting about 20mpg hwy. only 1 o2 was connected, it was throwing an o2 code. fixed that, added 2 brand new o2's. milage increased to about 25 highway, and 20 city. i changed the thermostat, and no help. the air filter seems to be clean. checked the vaccum lines, they arent leaking. tires arent underinflated. i hooked up a a/f meter today and its running stoich while cruising and just a little bit rich when i floor it. so i'm stumped, i'm guessing my next step would be to check the muffler?
ive read alot of stuff on this board saying to change the fuel filter, but that just doesnt make any sense. how would lower fuel pressure cause bad milage? and would cap/rotor really make THAT big a difference in milage? i'd really like to hear a qualified technician answer one of these gas milage posts with some good info rather than people just guessing what might help.

 

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