Sparky16

Hello all,

My 2006 TL has just under 95,000 miles, had timing belt, water pump and other related pulleyes replaced at around 91,000 miles.
After the WP/TB replacement, plus idler pulley, belt tensioner and serpentine belt all repalced, new NGk plugs as well, TL drives much quieter and smoother but still feels somewhat sluggish. It doesn't have the usual peppiness and responsiveness like it had a few years back. I also feel gas mileage isn't what it used be. I used get around 30-31MPG highways and averaged out 25-28MPG combined. Now it's like 25 or 26 mostly freeways,

I've read others getting better mileage after O2 sensor replacement, wondering replacing the O2 sensors would give me big boost in performance and better gas mileage.
How can you tell when you need your O2 sensor replacement? Or, do you just replace them after so many miles?
Do you replace both front and rear upstream O2 sensors? I understand NTK supplies OEM sensors but many members here reported as Denso O2 sensors work quite well.
FYI, I don't have any CEL or DTC code.

Please share your experiences and wisdom and shine some light on my problem. Thanks!

svtmedic

For o2 sensor replacement I always say, don't fix it if it ain't broke. As for mileage I drive all highway and I drive about 28,000 a year roughly. My car is 113000 miles on it and it is an 07 tl. I still average in between 28 and 33 only because I can't keep off the gas I'm a little bit heavy in that right foot. When I set my cruise control at 70 to 75 miles an hour I'm averaging between 33 and 37. Those are mid numbers. I personally believe my mid is a little on the Wild Side. But when I do the math comes out to about 30 to 31. O2 sensors will help. Assuming that your spark plugs and other maintenance are all done using the correct parts. If you have a scanner you can hook that up while you're driving and find out what your short-term and long-term fuel numbers are doing. That will tell you a lot.

horseshoez

iTrader: (2)

If you notice a rather sudden decline in fuel economy, more than can be explained by winter blended fuel and cold air, then consider replacing the upstream O2 sensors. If all is well, leave them alone; some fail in under 100,000 miles, others go way beyond the quarter-million mile mark. Said another way, a new sensor now may well need to be changed before the current ones you have in there need changing.

Sparky16

The decrease in MPG wasn't sudden, but was gradual. How do you know if the O2 sensor failed? When you gett CEL or some error dode, right? I don't have any of those, just slow loss of MPG.

For comparison, my 99 ML320.has 218k miles, but still has 3 original Bosch O2 sensors, just 1 was replaced about 80,000 miles ago, still going strong.

I would hook up my Autel scanner for STFT or LTFT, but last time I did that, triggered VSA error messagr afraid it might do that again.

horseshoez

iTrader: (2)

The thing is, O2 sensors often get "lazy" for lack of a better word, however, not lazy enough to trigger a code. What kind of fuel economy are you experiencing and in what conditions, and what was it when you considered it "normal"?

losiglow

iTrader: (1)

You'll typically fork out a good $100 per O2 sensor so yeah, I wouldn't replace them if you don't have to. But like hoseshoez said, if you notice a significant decrease in MPG or engine output it might be worth a try. As long as the O2 sensor voltage is between 0.1 - 1.0 volts it won't throw a code. But that doesn't mean it's running efficiently or is providing a very accurate voltage reading based on the fuel/air mixture. And if it does exceed 1.0 volts it could be a rich fuel mixture error as much as anything.

I'm not an electrical engineer or anything, so my evaluation of O2 sensors is based more on a basic knowledge of electrical equipment and mechanical crap in general. However, I can tell you that when I replaced my O2 sensors @ 100K miles, I didn't notice any change.

Sparky16

I would consider anywhere around 30 MPG as normal, maybe a bit under. The MPG I'm getting is right around 25, but I feel the TL sluggish and have to step hard for a lane change and passing. It's very unusual for my TL as I'm the original owner.

Sparky16

Since my TL is pretty close to 100k, it's probably a good time for new O2 sensors. I'm hoping to get some responsiveness back by replacing them.

Also, by replacing them on proper timing, will be good for the longevity of my TL, I'd hope.

What brand are you guys replacing them with?
Is Denso not good enough? NTK is the only accepted brand here?

horseshoez

iTrader: (2)

As a general rule, 100,000 miles is still pretty young for upstream O2 sensors; the ones in my Accord have 195,000 miles on them and they are still functioning perfectly well.

Denso is the preferred brand, do NOT put Bosch sensors in.

Sparky16

Yeah, thanks for the reminder, I also read Bosch o2 sensors doesn't work well on our TL.
95,000 miles isn't a lot but almost 12 years is quite a long time. I will probably replace both upstream o2 sensors with Denso ones for under $200 shortly, but wondering what else would cause the loss of peppyness. I haven't really got much of performance boost after replacing NGK plugs . . .

Sparky16

Yeah, thanks for the reminder, I also read Bosch o2 sensors doesn't work well on our TL.
95,000 miles isn't a lot but almost 12 years is quite a long time. I will probably replace both upstream o2 sensors with Denso ones for under $200 shortly, but wondering what else would cause the loss of peppyness. I haven't really got much of performance boost after replacing NGK plugs . . .

UA6andfriends

PCV Valve clogged?

horseshoez

iTrader: (2)

I disagree, O2 sensors do not typically have a calendar age issue; the factory O2 sensors in my 2001 Accord are still going strong; so too are the factory sensors on our old minivan which was built in early 1998. Like I wrote earlier, given the vagaries of how long O2 sensors last, replacing your sensors now at ~100,000 miles means you are pretty much just as likely to have a failure in the next 100,000 miles; leave them alone until and unless they fail. The odds the factory sensors will still be operational when you sell the car are pretty high.

Sparky16

I doubt that. I've been using the best gas available, 91, 92 or 93 depending on where I was, should be very clean at this low mileage. ALso, the TL passed California's strict smog check easily a month ago when I moved back to CA. The numbers are exceptionally good.

Thanks for your reply and advice. I don't mind saving $200 by leaving the o2 sensors alone, seriously. I agree that o2 sensors should last very long when used high quality gas all along.
But what needs to be done to improve the performance, the quick response I used get? Valve adjustment comes to mind, but the TL drives very smooth zero shakyness, I ruled that out.

losiglow

iTrader: (1)

Maybe try resetting the ECU Pull the negative terminal off the battery for about 10 minutes then reinstall it. Some say it's helped the 3G in particular, especially in regards to the transmission "learning" your driving habits. Some do it every 5-10K miles.

Check air filter, clean MAP sensor (with good quality electrical cleaner), check vacuum hoses for leaks. Or if you want to get a bit fancier, get the Torque App and a Bluetooth OBD reader and monitor your fuel trims. If they're off significantly, it can affect engine output.

horseshoez

iTrader: (2)

A few comments:

• I've never seen O2 sensors improve performance; their job is for more feedback/fine tuning of the mixture.
• Regarding improving performance, lots of possibilities. When you talk about "quick response"; are you talking about throttle response or are you talking about WOT acceleration?

Sparky16

By "quick response", I'm talking about throttle response not WOT. I feel slight lag with WOT acceleration.

I did have the ECU reset by disconnecting battery for 30 minutes at 4,000 miles earlier, but haven't felt any difference. I have new air filter installed about the same time as reset, but no MAF cleaning done.
I'll check for intake air leak by checking the hoses(don't have smoke generator) and monitor fuel trim, just to verify the o2 sensors' performing as they should.