Should I replace my O2 Sensor?

[Ihatecars]

I'll keep an eye out for any unusual smells.
I'm going to preform a slight experiment using a control of a single gas station, and alter a few variables. Such as my O2 Sensor, tire pressure, and driving habits. We'll see if there is any change or if I'm in bigger trouble than I'd previously anticipated.

[jnshk]

FWIW, when my commute consisted of a route that was mostly in-town highway (40-50mph, but heavy traffic) with some in-town stop-and-go, I would generally get 27-28mpg. Now that my commute consists of major highway (65-75mph) and slightly more in-town stop-and-go, I am getting about 23-24mpg average.

[psulja]

If you've done a tune up already and everything else looks like its performing fine it doesn't hurt to change the o2 sensor.

The car is performing properly, right?

If I was to do an o2 sensor I would buy this:
http://www.rockauto.com/catalog/more...627&cc=1190887

www.rockauto.com search for part number 2341024
$28.62 with the connector already in place rather than a universal sensor.

I have heard that it is not good to solder o2 sensor wires.

Dissimilar metals have a contact potential that varies with temperature. If the solder is between the two wires, any small temperature difference will create a voltage across the joint, hence giving a bad reading. This is called the galvanic effect and is the basis of how thermocouples are made.
Do not repair the wiring, the connector or the terminals. Replace the oxygen sensor if the pigtail wiring, the terminals or the connector is damaged. Proper oxygen sensor operation requires an external air reference. This external air reference is obtained by way of the oxygen sensor signal and heater wires. Any attempt to repair the wires, the connectors or the terminals results in the obstruction of the air reference and degrades the oxygen sensor performance

[— kung fu jesus —]

A few thoughts and experiences with my '92 and this issue.

First I wanted to address your original question; the narrow band O2 sensors on an OBD1 car has a range that is within spec. The O2 can degrade over time and still be within range, not throw a code. For a replacement, I prefer direct OE replacements such as the NGK or such 'known' brands. I do not like the splice-in type because the cable is shielded and a break in the shielding can allow static from a number of sources to dilute the signal. That is just my opinion. I have and do use a spliced-in rear O2 on my '99 because I added a custom midpipe and '01 manifold.

For fuel economy to decrease that badly over that amount of time I would be suspicious of other systems causing the drop. In my experience, the first items I would check would be the brakes. I would check the pads for even wear, stuck calipers, dragging emergency brakes. I have had that cause a huge swing in fuel economy. Brake maintenance is pretty simple, inexpensive and preventative. Usually all I did was remove the pads, retract the caliper pistons to see if the were binding, inspect the rubber boots on the mounting hardware for tears, water in the grease or debris, clean the slides, re-lube with a high-temp silicone grease, re-install the pads, sometimes bleed the system (depending on the amount of track time the car saw). I usually did this annually, sometimes longer.

The tire pressures, as mentioned above, are also pretty common. These cars are sensitive to uneven pressures, but if the tire(s) are leaking slowly over time, you may not notice it as much.

Also, I don't know if TX does this, but in some of the northern states the fuel formulas are changed from summer to winter. IIRC, the winter formula doesn't achieve the same economy as the summer version, but it isn't that bad as you are noticing.

So, before throwing parts at the issue, check the simple, free stuff first, deduce the issue from that by eliminating the possible variables and move to the next one. If you you really still feel it is the O2, you can hook a simple volt meter to the O2 and drive around to see how it responds and reads. It's a simple 5v circuit and the ECU monitors the output and responds accordingly. A narrow band O2 dithers a LOT, but if the O2 is bad, the readings at the volt meter will be relatively flat or sluggish across the range of driving.

Good luck!

[jnshk]

I would like to second the comments about "universal" O2 sensors. Ideally, it is better not to use them at all, but if you do then you want to crimp only. (Most of the time the wires are a stainless or othersuch metal which will not readily solder anyhow.) I believe that Bosch universal sensors include "posi-lock" connectors which allow you to securely join the wires by hand without any special tools, but as Steve mentioned you will still be breaking the shielding of the signal wires.

[Ihatecars]

UPDATE!

Okay, so I decided to do a bit of an experiment using gas stations, and an O2 Sensor as the variables. I'll also try to make my driving routine as constant as possible for the sake of my experiment. After two fill ups at the same gas station, getting the same gas, driving nearly the same distances, under the same conditions I got a constant reading of 26 mpg using Fuelly as my MPG tracking calculator.

This leads me to believe that the gas station I'd previously used had either a bad pump(I don't believe I fueled up at the same pump constantly) or they're thefts.

Today I ordered a complete Denso O2 Sensor to use for the next portion of my experiment.

I'll report back once I've installed the new sensor and I've also fueled up a few times.

[— artcentermiata —]

i dont think ive ever gotten much more than that before my rotrex...

i remember around 28mpg with normal driving and highway entrances (not eco driving, but not nutso driving)

now i dont get near that haha!

[Ihatecars]

But now you get to listen to all that awesome whining! I'd loves a few mpg for that.

[— kung fu jesus —]

I had the same pump issue happen to me on a recent roadtrip with another car. The fuel pump shut off and I hang it up thinking it was full. When I got in the gauge read full, but it started decreasing after a shorter time than before. I had also calculated my mileage on that fill up and it was much higher than the previous stops. I figure the cutoff in the pump kick on and probably still has 2 gallons or more to go.

Oddly, with this same car, I have had the cutoff NOT engage and gave the fender and immediate are near the car's filler a nice gasoline douching. :/

[Ihatecars]

I'm excited to see what type of differences a new O2 sensor will make.
I'm not expecting anything too great, but I'm excited to be able to reach 30mpg again.

[maharaj]

Just so you know, I hate all of you with your hybrid mileage miatas. Jerks.

[Ihatecars]

I'm not too excited about my hybrid horsepower.