ef civic - oxygen sensor retrofit

thought y'all might be interested to know that you can retrofit a 4-wire sensor onto an older 1-wire civic without upgrading to the obd1 ecu.
did this recently on my 89, and have been delighted to find my urban fuel economy has improved significantly - it's jumped from 29-30mpg crawling around san francisco, up to ~35mpg. no noticeable difference on freeway driving, but the overall average for mixed use improves.
i have the heater wired into the yellow/black wire that is the same circuit at the fuel pump supply and the fuel injectors, the sensor ground and heater ground common-connected to the engine block, and the sensor output wired onto the old sensor input on the existing harness.
note: this is not california legal for smog. even though it improves emissions because the ecu goes into closed loop much quicker and stays closed during prolonged idle, smog checks require the original 1-wire sensor to be present and wired as per factory. so, keep your old sensor, use it for smog inspection, then switch back to this 4-wire solution for daily driving. i used an old 4-wire socket from a junkyard civic and bullet connectors to make this easy, and so there is no permanent modification to the stock civic harness.
nomina rutrum rutrum

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