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Old 09-14-2010, 04:03 PM   #1
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need help with 02 sensor readings:civic vx

i have searched the forum and have not found anything recent on monitoring o2 sensor readings. i have read threads:"civic vx lean burn monitor" "vx 02 sensor readings" "interpret my o2 readings" and "o2 readouts". i have a 95 cx and i replaced the engine with a 92 vx engine. the car runs good overall, i sometimes wonder if the idle is uneven at times i get a check engine light code 48 for the o2 sensor after the car has warmed up and when i am coasting to a stop while in gear. i don't get the check engine light otherwise. i have no idea how old the o2 sensor is. i pulled it and looked at it and color wise i did not see any obvious problems. i used the helms manual to troubleshoot, as has been mentioned in other posts and it all checked out until i got to the part about changing the ecu for a known good one.
i then went to the method of hooking the dmm to the d14 and d16 ecu slots, and doing the monitoring. here is what i came up with.

when engine cold i got -.78 as expected.
after engine is warm, the idle ranges between about 0.3 to 0.4
with hard acceleration about -1.5 to -1.8, normal acceleration about -0.5
while coasting to a stop goes as high as 1.8 (at this value it appears to be where the check engine light trips)
when cruising at a steady speed it seems to want to sit at 1.13

so i am getting a very wide range of 3 or greater, and the idle value seems off a bit, and when i appear to be in lean burn i am getting 1.13 instead of around 0.5.

referring to tom o's comments previously,i don't think i have an exhaust leak but could double check that. the elevation where i live is high; around 4800 feet.

recently, i got 52mpg on a 300 mile road trip, driving about 55-60mph.

is there a way to bench test the vx o2 sensor? i am unsure of what to do next. thanks for any input.

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Old 09-14-2010, 05:49 PM   #2
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Re: need help with 02 sensor readings:civic vx

I had the same issue with my 92 VX. The LAF sensors tend to get "tired" after 200K miles and often need to be replaced at that point. I put in a lightly used OEM LAF I bought from a tuner shop to replace the worn out one. The 48 CEL code disappeared immediately and has not returned even once in the past two years and 50K miles of driving.

So, if it really bothers you, replace it. I did not notice any change in mpg or driving performance before or after the replacement. The main function of the LAF is to keep the engine emissions as low as possible.

Anyway, the dash light did disappear though, so that was helpful.

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Old 11-07-2010, 07:43 AM   #3
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Re: need help with 02 sensor readings:civic vx

about a month ago, i decided to just replace the o2 sensor. i bought it from
oxygen for was the L1H1 NTK 24300. i replaced the sensor and on the same road trip where i got 52mpg prior to replacing the o2 sensor, i got 56mpg after replacing the o2 sensor. I monitored the AF ratios after replacing the sensor and instead of getting the wide ranges between -1.8 to 1.8, i had a much narrower range of about -0.6 to 0.4. at any rate i have been happy with the results and am glad i replaced it. also, the check engine light disappeared altogether.
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