Changing my Oxygen sensors question?

[pbm]

I have 129K on my 2002 Buick Century (3.1 engine) with the original O2 sensors. I have no CELs and the car runs great. I do feel my MPGs aren't what they used to be and I am considering changing the O2 sensors.
Is this difficult on the 3.1?
Any tips?

I'll probably use Denso direct fit replacements.

What are your thoughts on changing them as a maintenance item at 129K w/o a CEL?

 

[OldCowboy]

I think I'd check other things first. Air filter, PCV valve, spark plugs.

 

[The_Jeff]

I would skip the special sockets and just go at it with a normal 7/8" or 22mm open end wrench. If clearance is tight like for the back one bonk the other end of the wrench with a hammer.

The factory puts antisieze on and they come out okay.

I had a 2000 century 3.1 and I think, but can't confirm as I don't have the sophisticated scan tool, that internal engine noise (piston slap) was causing the knock sensor to take timing and efficiency away.

 

[Turk]

Originally Posted By: OldCowboy
I think I'd check other things first. Air filter, PCV valve, spark plugs.


Yep, these 1st + Techron/Redline/Amsoil PI.

Then, the O2 sensors.

 

[ltslimjim]

^I agree. Does it matter how much torque or 'turns past snug' it takes for an 02 sensor to be completely seated during replacement with a new one?

 

[Dave Hess]

Maybe the sensor is getting lazy with mileage ?

 

[pbm]

My plugs, filters etc....are all good.
I'm getting about 22-24 mpg depending on how much highway vs. around town driving. I haven't taken a long trip with this car in awhile but I have gotten 32-34 mpg on the hwy @ approx. 70 mph in the past. I have had the AC running a lot lately so maybe my mileage isn't too bad.
I am just wondering if O2 sensors need changing at 130K even though the car is running good?

PS: This Buick has been one of the best cars I've ever owned and that includes (new) Hondas, Toyotas, Mazdas, Pontiacs,etc.. It feels as though it could do another 130K without a problem (if it doesn't rust out first).

 

[Eddie]

Why fix what is not broken or bad? Other checks first.

 

[pbm]

Originally Posted By: Eddie
Why fix what is not broken or bad? Other checks first.



Maybe your right.
I can get both Denso O2 sensors for about $80 and I wouldn't mind spending $80 to get better MPGs (and the piece of mind that comes with brand new parts)....

 

[The_Jeff]

Wow, your car's running great. Best I could do was high 27s for MPG on pure highway obeying the speed limit and getting bored. Knew it was a dud.

 

[DreamerGT]

Changed them on both of my cars, and I had no CEL or anything either. The crown vic had 130k miles, when I changed them It ran waaaay better, night and day difference. The Mustang had 111k miles, and It drove a litter smoother nothing big, like with the other car.

 

[GMBoy]

For $80 I would change them. You've got 129k miles and your O2 sensors are probably a bit lazy and that will cost you some MPG and you may also get some improvement in overall drivability. The CEL won't come on until they are way out of range and you may be be close but not enough yet to trip a code.

Of course - be sure all the other tune-up items are up to snuff too since bad plugs/wires won't be cured by O2 sensors. You say everything else is good - so go for it. Using the OEM Denso is also a good move...I never got quite the same quality or performance out of the over the counter Bosch ones.

 

[pbm]

Originally Posted By: eljefino
Wow, your car's running great. Best I could do was high 27s for MPG on pure highway obeying the speed limit and getting bored. Knew it was a dud.

About 5 years ago I drove from NY to Tennessee and got about 32 mpg per tankful with the AC on and the car full (myself and 2 passengers and gear). I got 34 on one tankful after getting a speeding ticket on I-81 in Wyttville, Va.
(I-81 was moving fast with fans heading to Bristol for the races, I was cited at 81mph but was just keeping up with traffic, it might have had something to do with my NY plates....)

The mpg's always drop considerably in around town driving. I used to get about 22-23 in the winter and 24-26 in summer doing a combination of hwy/intown driving.
This summer I've only gotten about 22 but it could be because I've been taking the Corolla to work more (which is 110 mile round trip of mostly highway).

Anyway, I probably will change the sensors...
Has anybody done O2 sensors on a late model 3.1 and is it difficult?

 

[Trav]

On an 2002 3.1 i would be more inclined to do the LIM gasket as preventive maintenance at 100K+.
For 80 bucks i would probably do the o2 sensors, they could be getting a bit lazy.

 

[pbm]

I had the LIM done in 2007 at approx. 80K using the FelPro PS gasket and new bolts. I did it as a precaution after a used oil analysis (the only used oil analysis I've ever had done) showed 28 ppm of potassium.
I haven't lost a drop of coolant since so I assume I'm good.
I changed over to PEAK Global about 2 years ago so I'm thinking there is no 2-EHA eating away at my Fel-Pro...

 

[ChiTDI]

I did all O2 sensors (3 in my case) and a MAF at 140k and the results were very beneficial. Engine was running good and mileage was slipping but generally ok. No CELs.
The engine now is very robust, performance and mileage is like new, and I look forward to crossing 200k.
Worth it in my case. Hope yours works out too.

 

[mechanicx]

I think it would be worthwhile to change the O2 sensor. On that application I think there is just one sensor 1 O2. I would change it and not bother with the sensor 2 post cat. I don't think anything performance wise would be gained by changing sensor 2. I'd probably go with an ACDelco O2 sensor.

 

[ltslimjim]

^I agree here generally speaking. AC Delco over Bosch for this app, anyway. If you can, get the closest to OE plug either way. I wouldn't get Bosch, unless money was tight.

 

[Bamaro]

I wouldn't bother until the CEL indicates a problem.

 

[1 FMF]

there are two articles in motor magazine, august edition which you should be able to read now, and a follow up in sept. issue which you may need to log in to see, or wait till next month.
http://www.motor.com/articles.asp
it's the foreign service article on CEL's and oxygen sensors and high NOx failed emissions.
in short, you can have a bad O2 sensor and not have a check engine light (CEL) or diagnostic trouble code (DTC) stored. What's happening is the O2 sensor is sluggish and not responding quickly enough under all operating conditions, not enough to throw a CEL but enough to cause high NOx and fail emissions. They say a sensor signal should rise from 0.175 to 0.8 volts, should cycle at least 16 times within 10 seconds at 2000 rpm, and to verify sluggishness you need a scope and do a snap throttle test- from idle mash the pedal wide open then release quickly, if the 02 sensor takes longer than 50ms to respond it's sluggish and should be replaced. They have also shown that to replicate O2 sensor failures the engine needed to be very hot, such as until the electric radiator fans have cycled on and off a few times at idle, to get O2 sensors to flatline and not respond, which then usually sets a DTC. A takeaway from the articles it seems is if you have a significant amount of miles and/or time on a set of original O2 sensors, simply replacing them is not a bad idea even if you don't have a CEL or stored DTC.