New O2 sensor = better mileage?

[paddlenbike]

Have any of you WITHOUT a check engine light ever replaced an O2 sensor and seen an improvement in fuel economy? Second, would replacing the front sensor ($57) do anything if the rear one were still original?

I have 115k on the odometer and no check engine light; fuel economy is down a bit to 16 city, 19 highway. While working on the 4Runner I lost the O2 gasket, which is $10 vs $57 for a whole new sensor with the gasket, which is what started this whole thing.

[Seanz0rz]

I replaced both and saw a small improvement. Denso from sparkplugs.com

[4x4mike]

My experience was with the air/fuel sensor (I only have one o2 sensor). In researching my issue at the time guys replaced the A/F sensor when they got a cel and mileage took a major dump. I had the light but mileage stayed the same. I replaced the sensor within 25 miles so I never saw the drop. After replacing the sensor my mileage did go up to 25 mpg (loaded highway driving) for about 3 tanks, after that it went back to normal.

In my reading guys got down to 8 and 10 mpg so the sensor needed replacing. I never saw anyone else get an increase. I wouldn't spend an extra $50 for the sensor just for short term gains. I believe the sensors have a 60-75k mile life but most last longer. Maybe buy the kit and shelf the sensor until you need it.

[4x4mike]

Sean, did your increased mileage stick around? Did they drop prior to replacement? Or did they just go back to normal?

[paddlenbike]

Maybe buy the kit and self the sensor until you need it.



That's not a bad idea. I might need it to pass smog next time.

Mine uses 234-4161 front and 234-4154 rear, which are apparently the identical sensor, just different wiring harness lengths. Each are $57 on amazon. For future reference Mike, yours was probably 234-9003 (air fuel ratio sensor) and is available for $107 on amazon.

1999 & 2000 49 State manual V6 4WD - Front: 234-4161; Rear: 234-4154
1999 California manual V6 2WD/4WD 4Runner - Front: 234-9003; Rear: 234-4153

[Seanz0rz]

I think I might be confusing 2 vehicles here.

I think I have 1 o2 on the 4runner. I replaced it and saw mileage return to normal. no Cel, just bad mpg

[YotaFun]

Sean it depends on the year and the emissions equipment.
96-98 Cali or Non Cali had 2 o2 sensors, 1 in front of the cat and 1 after.
99-02 is where it gets fuzzy,
Most are Cali spec and have a A/F ratio Sensor before the cats (yes that is plural there are two) and an o2 sensor after the cats.
I guess according to what Paddlenbike came up with the 99-00 non Cali spec uses two o2 Sensors like the 96-98.

FWIW back eons ago when I got my 4Runner, my first CEL experience was with the rear o2 Sensor, and while everyone believe that doesn't contribute to mileage, in my case it did, and dramatically as well as performance.
I was seeing a major decrease of about 5-6 miles per gallon as well as the truck running very sluggish. I would clear the CEL and the truck and mileage would be fine till it went through its cycle.
At the time I was young an stupid so I just got the cheapest one I could afford and threw it in (no name brand) CEL went away and mileage seemed to be normal.

Eventually through the years my front o2 sensor went and I replaced that with a Denso, and the CEL hasn't been back since.

However my mileage has been considerably more crappy by the day and I believe it is due to that rear o2 sensor, so in the next few week I plan to replace that with a stock Toyota one and see if that doesn't help me out a little bit

[paddlenbike]

All 4Runners have two O2 sensors, one before and one after the cat, regardless of make/model/year/emissons package.

96-98 are all pretty similar
99-00 get confusing due to CA emissions package, many of which use air fuel sensors rather than oxygen sensors.
01-02 are pretty much like the 99-00 CA models.

http://www.urdusa.com/More-Products-Oxygen-/-AFR-Sensors/c9_13/index.html
While you do see varying part numbers, most 96-00 non-CA trucks use the same sensor, they just have different wiring harness lengths and thus the difference in part number.

[Seanz0rz]

again, it has been a while since ive done it. if there were 2, i replaced both. i suppose i am mistaken with o2 sensors and cat. i only have 1 cat.

[paddlenbike]

haha, it's okay Sean, it is ridiculous how many variations there are.

[4x4mike]

This is my replacement Air/Fuel sensor for my '99, 4wd, SR5, CA emission 4Runner.

https://lh4.googleusercontent.com/-hC6mY_DdKFk/TbmXTnZUYPI/AAAAAAAAlwQ/gr8g_mj9ZSk/s800/DSC08385.JPG




Here is the old one. 89467-35020
https://lh4.googleusercontent.com/-dp3Y3P05RVg/TbmXVOT2hEI/AAAAAAAAlw4/67crwegTDKU/s800/DSC08390.JPG

[paddlenbike]

According to Amazon 89467-35021 is the Toyota part number and 234-9003 is Denso's part number.

http://www.amazon.com/8946735021-Toyota-Sensor-Avalon-Sienna/dp/B004GJ32EM

[4x4mike]

That's a deal. I needed mine right away as we left for a week and almost 1000 miles about an hour after I replaced the sensor. I didn't want to leave with the cel on.

[Robinhood4x4]

While working on the 4Runner I lost the O2 gasket, which is $10 vs $57 for a whole new sensor with the gasket, which is what started this whole thing.

That's what you get for trying to armorall your O2 sensor.

On my 93, the AFM (as opposed to your MAF) went out without a CEL and the mileage went down a lot. That was a $700 repair.

I've read that you can also try cleaning your O2 sensor.

[paddlenbike]

I went cheap and just replaced the gasket. This thing has been down for a month, so I just needed to get it back together and not wait even longer for parts. I have 1 more year until my next smog check and I think I will just replace the O2 sensor then. It was close to not passing last time...mainly because I have a federal emissions truck (only one cat) but still have to pass California standards, even with less equipment.

[paddlenbike]

On the opposite subject of fuel economy, I did my first high elevation drive since installing the supercharger. The truck is a completely different animal now, rather than dropping to 4th gear on long grades and maintaining speed, the truck now will gain speed (and pretty quickly) in 5th gear with little effort. I had a Hummer behind me driving like a typical douche bag on the way to Tahoe...he would ride my butt on the flats and downhills but EVERY hill we hit he would fall way back. Then he would pass a ton of cars in the slow lane on the downhills and every time we hit a grade his poor little Hummer would slow down and I would cruise right on by. That made the SC worth the purchase right there.

Until the RAV4 and Highlander showed up, we had an all-4Runner driveway at the cabin:
https://lh4.googleusercontent.com/-ZgN8BO0n7u8/T5VpsET-46I/AAAAAAAAGxE/5z-lhwbdtQo/s640/IMAG1128.jpg

[Obi..]

Little willy dude in little Hummer would slow down and I would cruise right on by, so basically your normal day on HWY 80.


Fixed. :D

FWIW I had a guy in one like yors, stock sleeper looking playing around with me on I-5 last week, I immediately knew what was up since everytime he'd get into the #1 lane and play catch-up I could hear it winding up.

Gotta say, I'm jealous now.

[paddlenbike]

I am anxious to see what kind of power URD gets out of this prototype.

[Seanz0rz]

ken, any more info on that?

[paddlenbike]

No, unfortunately it's just a prototype they are testing at the moment. The only other info I have is the dyno video, but URD hasn't shared the numbers yet.

http://s239.photobucket.com/albums/ff262/Gadget2317/?action=view&current=MVI_0394.mp4

I am pretty sure a TRD SC'd truck wouldn't lift the front end that much on a dyno, so I'm excited to see some numbers. I wouldn't count on CARB approval but I would love to see it go into production.

[Seanz0rz]

cool.

I forgot you had the supercharger. your reliance on the o2's might be even more important than us NA guys. they are inexpensive to replace, so i would try it out.

[paddlenbike]

I bought a wideband and hope to install it in the coming weeks. The wideband should give me some indication how healthy (or not) my O2 sensors are.

Sean, if/when URD comes out with the Rotrex SC, I challenge you to a race at the Sand Drags @ Pismo. I'm not so sure I would put money on it though, that prototype looks to be a beast.

[YotaFun]

Interesting, can't wait to see what URD does with it, a pro charger would be cool.

[paddlenbike]

It took me nearly two years, but I finally placed an order through Amazon for a new front Denso oxygen sensor for $57. My mileage has really plummeted lately and my oxygen sensor is original, so hopefully this will make a difference.

[scottiac]

Let me know how that goes... I'm suffering the same mileage suck-mo these days. Down to sub-14 from 18-19 with no other changes except gittin' old.

[4x4mike]

Scott it seems that recently all my trips are short so my mileage has gone way down. I used to get 150 per half tank no problem but now I seem to only get around 220 for the entire tank.

I think an new O2 sensor will get better mileage but it will be short lived. Maybe combined with other maintenance items you can get back up there. Perhaps the misfire has something to do with the decrease?

[Robinhood4x4]

When the O2 sensor in my 93 went out years ago, the mileage plummeted. That's how I knew something was wrong.

[scottiac]

Beats the hell outta me. At 200+ a tank (what I'm getting too), it's hard to think of the 4runner as a viable long-trip vehicle. I actually stole Molly's Subaru for my last multi-state extravaganza. Almost humiliating, that, but her 700 miles per tank beats my 200 all hollow.

[Seanz0rz]

I get 250 from full to fuel light coming on (approximately 3 gallons left). But the 4runner is over weight, tall, and bricked shaped. That is also at 70ish mph. If I do 55 or 60, I get closer to 20 mpg.

[scottiac]

Right now, at 250 miles, I would have been pushing for the last 10... :-)

[paddlenbike]

A larger fuel tank is the #1 thing I would change about 3rd gens. My low fuel level light is overly protective; if I go to the gas station as soon as the light comes on, it only takes 13 gallons of fuel in its 18.5 gallon tank. But even on a good day, 300 miles is about as far as it will safely go on a tank.

But something has changed recently. If I kept my speed around 70 mph, I could always get between 20 and 21 MPG. (I got 20.8 MPG on a trip I took in April.) Now I'm getting 17 MPG. I did go to a 17" wheel and a 1/2" taller and wider tire with more aggressive tread, but I wouldn't have expected a 4 MPG drop. That's why I think something else is up. My O2 sensor is original, so I'll start there. I also put my factory roof rack back on yesterday.

Scott, good to see you on UY!

[YotaFun]

Ken, you would be surprised!
My buddy has a 97 5spd, he put a set of 265/75/16 Duratrac tires on his truck and his mileage plummeted.
I gave his a set of 5 stars I had on 265/70/16 Michilen CrossTerrains and his mileage is back up again.
Tread pattern I feel has a lot to do with your mileage, I even noticed a huge drop as well when I went back to the 33s and the aggressive tread.

[paddlenbike]

Ken, you would be surprised!
My buddy has a 97 5spd, he put a set of 265/75/16 Duratrac tires on his truck and his mileage plummeted.
I gave his a set of 5 stars I had on 265/70/16 Michilen CrossTerrains and his mileage is back up again.
Tread pattern I feel has a lot to do with your mileage, I even noticed a huge drop as well when I went back to the 33s and the aggressive tread.

Maybe so. I felt like I could do no wrong with this truck when it came to fuel economy. I lifted it and put on bigger tires, mileage stayed the same. I supercharged it, mileage stayed the same and actually went up in hilly terrain. So I figured when I went from a 50 pound 265/75R16 BFG (load range D) to a 50 pound 275/70R17 (load range C), that mileage would also stay the same, but apparently not.

[YotaFun]

I still want to change out my rear o2 (its a bosch I believe) and see if that helps, when it first went I remember the truck would run supper rich and I would get like 10MPG.

The front is newer within the last 5 years and it is a Toyota sensor, or at least a Denso equivilant

[paddlenbike]

As you know, Bosch parts don't seem to play well on our trucks, particularly spark plugs and O2 sensors.

I have a wideband O2 meter in the truck and the AF ratio is pretty steady at 14.7:1 at idle, but anything above idle and it's all over the place. I know the nature of a narrowband O2 on a federal emissions vehicle like mine bounces between rich and lean because it doesn't know the actual AF ratio, but my swing is quite large. It should be interesting to see if anything changes with the new O2 sensor.

[YotaFun]

Yes I know, but I was a poor 18 year old kid who needed his truck to pass emissions and got the cheapest sensor at the time -_-
I'm surprised it hasn't failed yet again, but then I do remember the design of it, and I am a little reluctant to change it because it may throw a P0420 code and thats the last thing I want to deal with right now -_-

I look forward to seeing your results on the changed out o2

[paddlenbike]

I look forward to seeing your results on the changed out o2

Don't hold your breath! The saying "you have to pay to play" is finally coming true with my truck!

[CJM]

Bigger tires for sure kill mpg depending on your setup. I went from 31" (actually measure 30.5") highwayish hankook all terrains on 15's to 265/75/16 dueler revos on 16's. Mpg however didnt change significantly because the smaller tires caused me to be geared a bit high and running about 2900rpm @ 60-70mph. The speedo was actually reading slightly low with them. The duelers the speedo is DEAD on and Im running about 2600rpm now at same speeds. Mpg-dropped maybe 1-2mpg at most.

[YotaFun]

Don't hold your breath! The saying "you have to pay to play" is finally coming true with my truck!

Yeah but I have been paying with a 10City/12hwy average when other can still get at least the EPA estimated 16/19?
You are right something has got to give!

[paddlenbike]

I was prepared for a fight with the O2 sensor tonight. On 5-speed 4Runners, the O2 sensor connector plug is sitting directly on top of the transmission, with no room to reach up, squeeze the plug with one hand while pulling with the other. I read a tip online to remove the O2 sensor from the exhaust and to pass the sensor over the transmission and pull down from the other side, which makes the connector easy to reach. Whomever wrote that tip, thank you, you turned this into a five minute affair.

Took it for a spin and it doesn't drive any different, but the wideband O2 meter I have installed seemed to change readings a little quicker, so maybe my old sensor was getting a bit lazy. I'm not expecting miracles, but I topped it off with fuel and made sure the tires were properly inflated, so hopefully there will be some improvement in economy.

https://lh4.googleusercontent.com/-_WeKa9nQxdE/UsuC9hdqU1I/AAAAAAAAMWI/oDBOI8l3MIc/s640/O2sensor1.jpg

Forward sensor is for my Innovate wideband, the one behind it is the new Toyota/Denso O2.
https://lh3.googleusercontent.com/-EjGFti8BCUY/UsuC9388tOI/AAAAAAAAMWM/MeXcBIpkcnI/s640/O2sensor2.jpg

Ken

[garrett]

Any updates? I usually average around 17 mpg with 265/75/16s... I'm not sure if my o2 sensors have ever been replaced.

[paddlenbike]

Any updates? I usually average around 17 mpg with 265/75/16s... I'm not sure if my o2 sensors have ever been replaced.

It does appear that the mileage has improved. That said, I have only run one tank of fuel through it since the O2 sensor was replaced--it was a ski trip (7,000+ ft of elevation change) along with some city driving. The tripmeter is showing 225 miles with a quarter tank remaining, whereas before the O2 sensor change I was closer to 180 miles by 1/4 tank remaining. Because the bi-product of burnt ethanol coats O2 sensors and makes them lazy, I would suggest spending the $57 if you haven't changed it for a while.

[slomatt]

Option 1: aka "If you are lucky"...


I was prepared for a fight with the O2 sensor tonight. On 5-speed 4Runners, the O2 sensor connector plug is sitting directly on top of the transmission, with no room to reach up, squeeze the plug with one hand while pulling with the other. I read a tip online to remove the O2 sensor from the exhaust and to pass the sensor over the transmission and pull down from the other side, which makes the connector easy to reach. Whomever wrote that tip, thank you, you turned this into a five minute affair.


Option 2: aka "Doh!"

On the first day of O2 replacement you install the rear sensor in 2 minutes, no problem. You then smugly pass the front O2 sensor over the transmission, feeling good that you know the trick to make things easy... and then find out the plug is bolted to the top of the transmission and still unreachable. After 30 minutes of getting grease all over your arm from the front driveshaft and poking around blindly at the connector on top of the transmission you think you've found the release button, but it is buried under 3 other cables and your fingers are numb from trying to press it. You then remove the center console and the shift lever and see if things are more accessible from up top, which of course they aren't. At this point you can somewhat see the connector, but can't reach it. And you can see the bolt that holds the bracket in place, but can't reach it. But, you can see that there is only 1/2" of free wire between the connector and the harness and that explains why you can't get to the release tab from below. Oh, and that cool short throw shifter which raises the shifter pivot point by 2" just makes things worse and harder to access. Defeated you grumble to your wife and have a beer, planning to somehow magically use locking pliers to hold down the tab from the top and then disconnecting the plug from the bottom, yeah, that'll work.

On the second day of O2 sensor replacement you quickly realize that the locking pliers idea is not going to work due to the ginormous short throw shifter housing and the very short leads coming out of the O2 sensor plug. So then you try using other random pliers to hold down the tab but now the tab is just looking a bit beat up. Your initial hope fades. Ok, there's got to be some kind of trick here, what am I missing? I bet I could use a crazy combination of flexible couplers and extensions to get to the bolt that holds the bracket in place, except a: you can't reach it and b: when you finally get a wrench barely on it there is no way you can apply enough torque to remove it, oh and c: you'd never be able to get it back on anyway. Ok, that's it, time to bring out the big guns and drop the cross member so you can lower the transmission and see what the hell is going on up there. Oh, but of course the 4 bolts that hold the cross member in place are on bubba tight and slightly corroded (no other bolts on the truck are of course, just these ones) so after 20 minutes of swearing and intense wrenching they are now loose. The floor jack comes out and you lower the transmission about 2" which is as far as it will go. Shafts of heavenly light shine down and you can now see the f*%#ing connector through the transmission tunnel, but still can't really reach it or the bolt for the bracket. Oh, and both rechargeable LED lights you received for Christmas are now out of batteries and you are starving and really have to take a leak but this is war and there is no time to pause for trivial personal needs. In the dim last gasps of the light you can now see the plastic clip where the plug attaches to the bracket, and after 5 minutes trying to compress it with every pair of pliers you have you finally say screw it and use a combination of a screwdriver and wirecutters to destroy the tab and separate the O2 plug from the bracket, to then realize that the 1/2" leads from the O2 sensor are because some sadistic Japanese Toyota employee (3rd gens are made in Japan) got a little happy with the tape and the wire loom and left no spare wire at all. So, out comes a razor blade and the desperate hope that you don't nick or sever any wires while cutting apart the loom through a 2" hole between the crazy-tall shifter and the sharp steel of the transmission tunnel using the now pretty much not there last volts of the light's battery. Reaching in with your longest needle nose pliers you are able to tear out the last piece of tape, and suddenly the O2 sensor connector (still tightly plugged together) is floating free. Then it's just a simple 5 minute task to pull the connector down from underneath, remove and replace the O2 sensor, run it back over the top, zip tie the connector to the now mangled bracket, and then bolt the O2 sensor in place to the prescribed 14lb/ft (168 in/lb if that is what your torque wrench is happy with like mine is). Victory!! Oh, and then the 15 minutes it takes to raise the transmission back into place, look up the torque settings for the cross member (54 lb/ft) and bolt all that mess back into place. Oh, and then the 15 minutes it takes to put every tool you own back into the toolbox since you had pretty much everything out at some point during this simple task that took ~3 hours over 2 days.


That got a bit long winded, I appologize. The summary is: Pass the sensor over the top of the transmission, if the connector falls down the other side then you are all set. If not, at least now you know the torque settings for the cross member bolts. Oh, and don't install a short throw shifter.

- Matt

[paddlenbike]

I suspect I got off easy. I had work done on my transmission a long time back, and consistent with my theory that "if you want it done right, do it yourself," the mechanic failed to reattach the wiring harness to the clip. Perhaps it was a blessing in disguise. I am sorry for misleading you, perhaps my direction to others would be to cut the clip that retains the harness--it's not like the wiring harness is going anywhere.

[4x4mike]

Yep, Ken got off easy. Matt, my replacement was very close to yours except for the rechargeable lights and lowering the transmission. It did get bad enough that I did consider lowering it. IIRC I didn't have to remove the short shift kit but considered it, even trimming the sheet metal in the tunnel.

My tools of choice were inspection mirrors and seal picks. The SOB bracket is now held in place with a zip tie.

[garrett]

Wow - thanks for sharing mike and matt. I was thinking about doing this soon but I think i will be doing a little investigating underneath before diving in. Would have never guessed it would be this time consuming.

[slomatt]

Wow - thanks for sharing mike and matt. I was thinking about doing this soon but I think i will be doing a little investigating underneath before diving in. Would have never guessed it would be this time consuming.

Garret,

This only applies to 5 speeds, which it looks like is what you have. :)

There are two relatively easy tests to see how things will go:
1) Unbolt the front O2 sensor, pass it over the top of the transmission and see if the connector comes down on the other side.
2) Remove the shift boot and look through the hole in the transmission tunnel towards the front of the car. See if the grey plug is attached to the bracket or not.

- Matt

[Kryptoroxx]

Matt I experienced the o2 sensor ordeal but it was when I was changing my clutch. I am pretty sure I improved the design when I didn't use that particular area putting it back in.

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