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California98Civic · 07-21-2014, 08:31 PM

It seems the O2 sensor on these is not as critical as a lot of people think. It is critical to engine management, and if your O2 is bad enough to set off the check engine light, you will not get lean burn. But when the engine goes into lean burn it is in open loop and the air/fuel ratio is set by the computer, without the O2 sensor. There are a couple recent threads on EM where this topic came up. I was on the losing side of the debate, with the position I just described being correct instead.

I imagine the engine computer still monitors the 5-wire O2's finer wide-band data stream to protect the engine itself?

I looked at the FSM. The 1996-2000 FSM does not list the O2 or data that would come from it in the parameters for lean burn. It does say that a check engine light, for any purpose, will keep the car out of lean burn. Of course a VX is OBD1, not OBD2, but I don't think it is any different in this regard.

Normally, on this site, we have described the o2 as essential to lean burn, but apparently it is not.

07-21-2014, 08:31 PM	#10 (permalink)
California98Civic Cyborg ECU Join Date: Mar 2011 Location: Coastal Southern California Posts: 6,302 Black and Green - '98 Honda Civic DX Coupe Team Honda 90 day: 66.42 mpg (US) Black and Red - '00 Nashbar Custom built eBike 90 day: 3671.43 mpg (US) Thanks: 2,374 Thanked 2,176 Times in 1,471 Posts	It seems the O2 sensor on these is not as critical as a lot of people think. It is critical to engine management, and if your O2 is bad enough to set off the check engine light, you will not get lean burn. But when the engine goes into lean burn it is in open loop and the air/fuel ratio is set by the computer, without the O2 sensor. There are a couple recent threads on EM where this topic came up. I was on the losing side of the debate, with the position I just described being correct instead. I imagine the engine computer still monitors the 5-wire O2's finer wide-band data stream to protect the engine itself? I looked at the FSM. The 1996-2000 FSM does not list the O2 or data that would come from it in the parameters for lean burn. It does say that a check engine light, for any purpose, will keep the car out of lean burn. Of course a VX is OBD1, not OBD2, but I don't think it is any different in this regard. Normally, on this site, we have described the o2 as essential to lean burn, but apparently it is not. __________________ See my car's mod & maintenance thread and my electric bicycle's thread for ongoing projects. I will rebuild Black and Green over decades as parts die, until it becomes a different car of roughly the same shape and color. My minimum fuel economy goal is 55 mpg while averaging posted speed limits. I generally top 60 mpg. See also my Honda manual transmission specs thread.