Oxygen Sensor Questions

highlife · Post by **highlife** » December 19th, 2005, 8:49 am

I'm getting 24 mpg on my 1993 1.6 5spd. Idid the voltage test on the O2 sensor and got .79 volts at idle and .85 - .89 volts when above idle. The chilton book I have said 0 - .4 volts at idle and between .5 - 1.0 volts when raced. Question : Will O2 sensor failure alone cause the control module to default to some kind of gas sucking safe mode or is it just one bad signal from the O2 sensor and the ECU is still in 'normal ' mode ?

This started after I replaced a slipped timing belt. I have double checked that the belt is aligned correctly and the timing is exactly 10 BTDC. I tried the ecu reset but no effect. The car runs normal other than poor fuel mileage. I did drive the car for a couple days with the timing slipped before finding the problem, would that have killed the O2 sensor ?

thanks for any thoughts...

Focal · Post by **Focal** » December 20th, 2005, 7:53 pm

i was wondering the same thing due to the fact i have now started to get poor fuel economy also.

reprobation · Post by **reprobation** » December 20th, 2005, 9:07 pm

Wow, thats got me questioning if something is currently wrong with my system... i get about 180-200 miles per tank... that averages me a 21-22 MPG....

The only that im not running stock is my Cold air intake... but i don't think it'd make that big of a dip in my efficency... maybe i should look into replacing my o2 sensor too...

how long do they typically last? I bought my mx3 at 64k miles, currently at 95k ... i have seen a stead decrease in efficency...

Focal · Post by **Focal** » December 20th, 2005, 11:18 pm

well the 4cyl are supposed to get crazy good gas mileage when i first got my car i was getting close to 500km per tank and it has steadily dropped

mx3optidrive · Post by **mx3optidrive** » December 21st, 2005, 9:17 am

could be your catalytic converters being clogged too. Mine was and when I hollowed it out, everything was back to normal.

Devilhog · Post by **Devilhog** » December 21st, 2005, 7:57 pm

Probly is a bad o2 sensor. I dont even have mine in atm and im getting 20 mpg.

When I got my 96 1.6l DHOC I was getting about 550 per tank. Im hoping once I get my car tuned up and the new o2 sensor it will hit around 500 again.

highlife · Post by **highlife** » December 21st, 2005, 8:53 pm

I replaced the sensor $20 for a bosch universal, havent burned enough gas yet to do the mileage but will post back with my results. Performance is much smoother - RPMs will 'hang' now in between shifts where they just dropped before. This car/engine is originally rated 35 mpg highway so should be able to get at least 30 on average.
I checked everywhere for a leak when the mileage first went to hell and found nothing. I now notice a raw fuel smell around front of car when I first get out after parking but it doesnt last and is gone within a minute.
Anyone know of any common weak points in the fuel system ?

Focal · Post by **Focal** » December 23rd, 2005, 6:59 pm

What O2 sensor did you replace? Was it the one on the exhaust manifold?

highlife · Post by **highlife** » January 2nd, 2006, 2:40 pm

Focal wrote:What O2 sensor did you replace? Was it the one on the exhaust manifold?

Yes.

Bochek · Post by **Bochek** » January 2nd, 2006, 10:47 pm

an o2 sensor is only designed to last between 60-80k miles. and they are the #1 cause of bad gas milage (besides having a heavy right foot).

they seem to be way cheeper in the USA for some strange reason.

and its ok to get a aftermarket one as long as the voltage and temperature ratings match.

Bochek

highlife · Post by **highlife** » January 10th, 2006, 1:21 pm

Just filled up - my mileage is actually worse, 23 mpg. I guess I'll have to look elsewhere for a culprit although does definitely run smoother with the new O2 sensor. After I put the new O2 sensor in I didnt reset the ECU because the CEL was not on. Do you think I need to do this even if the CEL does not come on ?

ryanlindenberg · Post by **ryanlindenberg** » January 10th, 2006, 2:03 pm

highlife · Post by **highlife** » January 11th, 2006, 10:07 am

ryanlindenberg wrote:yes

I will try resetting the ECU, what the he!! - but it doesnt make sense that it would need to be reset if it didnt recognize the bad signal in the first place....