Are all O2 sensors created the same...

[rasouth]

Hey guys and gals! I've got a '96 4.0 XLT OHV Exploder (yes, Exploder), and I am getting crappy fuel mileage. (around 11 to 12.3 in town) I am thinking it might be the O2 sensors. They haven't been changed in at least 80,000 miles and I cannot remember if that was the upstream or downstream, or if it was just one. Looking around on some auto parts web pages the say "Upstream Left or Right" or "X Engine Code". I believe I've got two upstream and one downstream sensors. My questions are, is there a difference between left and right upstream sensors? Do I need to replace downstream sensor? What brands would you recommend?
I am not throwing any codes at this time. I have done a tune up of plugs, wires, coil pack, oil change, cleaned the MAF, throttle body, air cleaner, etc. I still need to do tranny fluid and filter change soon.

 

[1998Exp]

Hey guys and gals! I've got a '96 4.0 XLT OHV Exploder (yes, Exploder), and I am getting crappy fuel mileage. (around 11 to 12.3 in town) I am thinking it might be the O2 sensors. They haven't been changed in at least 80,000 miles and I cannot remember if that was the upstream or downstream, or if it was just one. Looking around on some auto parts web pages the say "Upstream Left or Right" or "X Engine Code". I believe I've got two upstream and one downstream sensors. My questions are, is there a difference between left and right upstream sensors? Do I need to replace downstream sensor? What brands would you recommend?
I am not throwing any codes at this time. I have done a tune up of plugs, wires, coil pack, oil change, cleaned the MAF, throttle body, air cleaner, etc. I still need to do tranny fluid and filter change soon.

Not an expert, so take my humble opinion with a grain of salt!
2nd gen Explorers are rated by Ford at 14 MPG in the city. We all know that it's exaggerated, so your 11-12 doesn't sound all that bad to me. It also depends on what "in town" means. It could be a 50 MPH street with a stop sign every mile, or a busy downtown with a 25 MPH limit that you can't even reach because there is a light on every block. As for the sensors, the downstream one is just a monitor, and does not affect engine performance. For the upstream ones, to the best of my knowledge, the only difference between right and left is the length of the wire harness. You can use the longer one in the short position and tack the extra length somewhere, but not the other way round. The effect on MPG? Some people claim that they become sluggish at around 100K and degrade MPG. How much? My Ex (a 1998 V8 with 175K miles and original O2 sensors) is now experiencing about 5% MPG degradation, compared to when it was new. I drive it so little these days that it doesn't make sense to spend the money or the hassle to replace, especially the one that is only accessible through the floor. Your mileage may vary. Good luck!

 

[Hacra]

The main working principle is the same with 150$ and 10$ o2 sensor if we are not talking about wide band ones (which you do not have).

Afaik the purpose of the other O2 sensor is just to check the functionality of the other, how the pcm interpets this information is another story. (someone wiser should hop in to the discussion at this stage).

If you want to diagnose your O2 sensors i'll throw in a picture to check external problems and picture how to connect wires.

Also i think forscan will display sensor input values?

Ps. rockauto has ready O2 sensors with wiring kinda cheap.

Also if you end up using cheap universal O2 sensors, you will be tempted to solder the wires, but DO NOT, this will cause the O2 not to work. Crimp the connections.

Similar guides can be found with google, i hope this helps.

 

[Turdle]

The downstream sensor(s) merely monitors the function of the catalytic converter(s)
My .02 is
Replace upstream as a pair with OEM equivalent. They are not created equal. The part number difference is for wire length difference.

 

[rasouth]

One reason I am thinking of replacing O2 sensors is because a few years ago I had a warped head that was leaking coolant into the cylinder, blowing water out the tail pipe, caused an error code for the cat converter. No code since replacing head but I am sure the O2 sensors were affected some what.
Thanks for the pics Hacra. This will come in handy. Maybe I will pull O2s and see what they look like first before spending money. Any idea how they should look if they are not contaminated with fuel or oil?
And to you, 1998Exp, what I mean as "in town" is mostly under 40 mph, stop signs or stop lights every 1/2 mile, waiting in the McDonalds drive through, driving less than 5 miles a day. My parents bought the car new in '96 and I got it in 2013. My dad always had the services done on time, tune ups, tire rotations, etc...I could have sworn when I got the car it was getting close to 16 to 17 mpg around town, ( the same town I've always lived in), and I got 32 on open roads through the desert highways. It has 204000 miles on it and I do not expect it to get ideal gas mileage, just hoping to get a little more out the ol' girl.

 

[Hacra]

If the o2 sensor is original the tip should look quite black from carbon residue/build up, if not, refer to picture above.

In your case external contaminant (coolant), might have "washed" the sensor tip. Compare different sides, if other head of the engine did not have coolant leak the o2 sensor should look different.

 

[410Fortune]

I would be looking at doing a tune up not replacing 02 sensors
You likely need to check/replace the following:
air filter
fuel filter
spark plugs
spark plug wires
clean the MAS
Check tire pressures
Check rolling resistance
Check for leaks around the intake plenum O rings
This is a basic tune up on a 4.0 pushrod that is not getting the MPG it once did

If your 02 sensors were effected by water in the exhaust then they would be in big trouble since water in the exhaust is a product of combustion so it is always there, you can always see water dripping from a tail pipe when the vehicle is cold started....water vapor is always in the exhaust side of things at least until the exhaust gets hot enough to turn it to steam.......and if your 02 sensors were having issues with the pre heater circuit or their ability to monitor 02 levels in the exhaust you would get a check engine light

 

[rasouth]

Thanks for the info 410Fortune, but if you read my complete post I said I already had performed a tune up of plugs, wires, air filter, etc. I did not mention that I got two new front tires and a wheel alignment so the tires have the correct pressure. I also mentioned that I have replaced the head, so, therefore, I replaced all upper gaskets, including the plenum O-rings. I do not believe there is a leak around the intake.
One reason I am asking about the O2 sensors is that I read somewhere that O2 sensors should be replaced around 100,000 miles.

 

[Hacra]

This is purely personal opinion, but i think of it like brushing teeth, preventative maintenance. If changing them isn't financial burden every some years, why not; if the pay back is peace of mind and reliability.

O2 sensor for these cars are relatively cheap (under 100$ for all 4 and gets even cheaper if you use universal). Changing them might be mildly annoying (due to access to connectors being quite annoying).

 

[C420sailor]

Check for dragging brakes. Is the vehicle coming fully to operating temp?

I haven’t changed my O2 sensors in 100k mi and the fuel mileage hasn’t changed one bit. My Trucklet gets around 14mpg around town, 20-22 on the hwy. SOHC w/ 136k on the motor, though. I think the OHV is a smidge less efficient, so maybe you aren’t thaaaat far off?

 

[rasouth]

I did a brake change not long ago. No indication of brake drag. No problem with the temp. Replaced radiator 4-5 years ago, along with thermostat.
The O2 sensors are just the last on a "to do" list, trying to keep her going for a few more years. Some people say "If it ain't broke, why fix it?" and others say "A stitch in time..."
Thanks for all the input and info, guys and gals.

 

[1998Exp]

When you replace the O2 sensors, please let us know the MPG improvement.
In the meantime: if your main usage for the vehicle is driving less than 5 miles a day, much of your driving is with a cold engine, and you cannot it expect it to reach the specified in-city MPG.

 

[410Fortune]

Dang sorry I missed all of that
Yes 02 sensors do wear out over time, their responses get slower and the heater circuit well its a heater element that heats up with voltage applied, we all know things that heat up wear out more quickly.
So it is a good idea to replace them every 90-120K or so, I agree

Years ago I would have told you if it ain't broke don't try to fix it when it came to 02 sensors...

I am older and wiser now because I have actually seem an improvement with MPG and performance by replacing old worn out sensors that were still functioning just fine according to the PCM

 

[J_C]

It's a bit of both, "if it ain't broke don't fix it" and a stitch in time.

If you were having a problem, I'd say sure if it seems O2 related then replace them. If the problem is that you're stuck on this issue, if you replace them then you can move on to doing something else.

Eventually they will result in enough fuel economy improvement to pay for themselves, but our crystal balls aren't accurate enough to know if it will for any particular vehicle. A deer could run out in front of it, or it could get struck by a meteorite, or a texting teenager, etc.

You can replace every last little part on a 24 year old vehicle and that will benefit some people and be a waste of money for others whose vehicle didn't last (enough) longer to get the value out of the parts.

Personally, I wouldn't replace them without cause. I wouldn't sink any more money into a vehicle that age until it was needed. If it's a daily driver then I would put the money aside to replace it, expecting one of the far more common reasons a vehicle is retired. Few vehicles ever hit the junkyard because of an O2 sensor.

On the other hand, O2 sensors are not expensive for these. It's not a bad decision either way, so the easier course of action is focus your attention on something else in life that needs it more. I know I have a lot of other things that rank higher than my O2 sensors.