Question about 1993 Honda Accord

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93 Accord Oxygen Sensor Confusion

I recently replaced the Oxygen Sensor on my 1993 Honda Accord EX, and ever since doing so two funny things have happened. The first is that my check engine light is illuminated occasionally when I start the car from completely cold (i.e. starting after sitting 3+ hours). If I turn my engine off and then immediately start it back up the light does not come back on. Second, my gas mileage has gotten WORSE since the change. I've noticed a loss of 2-4 mpg over extended trips and that my RPMs are higher than they were before the switch. For example, I used to run about 2,600-2,800 RPMs going about 60 MPH depending on driving conditions and since the switch the RPMs are rarely lower than 2,900 at 60 MPH.

My obvious concern is that I've only ever heard of a new oxygen sensor fixing an illuminated check engine light, and that mileage always improves once the sensor is replaced. I'm seeing exactly the opposite.


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  • stephen_krau Nov 18, 2008

    I did the ECU reset number and my highway RPMs went back to normal, which is strange according you what you said, because I did change the tires. The tires that came with it were 195/65/15 which apparently is the wrong size so when I got new ones I got the right size 195/60/15. Anyway, I haven't fueled up since so I have no idea if my MPG is back where is used to be.

    Problem is the "check engine" light still comes on after cold starts, and the same fix works to get the light to stay off (kill the engine start it back). I did notice however that when the light is on my idle speed is higher than normal, it basically hovers just above or just over 2k RPMs... any clue as to what's going on?


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Did you reset the ECU after changing the sensor? If not you need to (procedure in 2nd pic below), that way the fuel trims are reset and the ECU can re-learn the Short term and Long term fuel trims. this could be the cause of the difference in MPGs.

An O2 sensor will have no effect on RPMs/MPH. the only thing i can think of that would effect this besides changing gear ratios, would be changing the overall diameter of your tires or possibly a slipping clutch.

Check the codes on the ECU. here is the procedure:

93 Accord Oxygen Sensor Confusion - 65a6b8a.jpg d43f356.jpg

Posted on Nov 15, 2008

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