Replace the Oxygen Sensor to Improve Mileage?

[lothian]

2000 Honda Accord 3L-V6 w/105k miles. This car has maintained its original mph rating remarkably well over the years. But fuel economy has dropped off measurably these past few months–reasonable, I think, given the age and mileage–and with the suddenness I suspect a specific problem.

The Actron presents no codes, so I am struggling to find the source. Within the past month, I replaced:
– tires: Dunlap Sport Signature
– plugs: Denso Iridium Spark Plug
– fuel injectors: Python 621-304 Injector
– the usual whatnots (e.g., new air filter; cleaned the EGR ports in the plenum and intake; cleaned the throttle body; checked for vacuum leaks; etc.)
…all with nil effect on the Accord’s fuel mileage.

I understand that t-shooting negative fuel economy issues runs a very wide gamut. I’ve covered the cursory items, so I am operating under the presumption that outside of something extreme or peculiar, the most likely culprit(s) is/are old, original parts. Therefore, what relevant, aged part is prudent to systematically clean or replace next? ..the oxygen sensor(s)? …PCV? …EGR? …MAP? …IACV? I mean, all parts have a replacement threshold, right?

As for the subject of this post…
The short term fuel trim readings, which fluctuate under load, of course, appear to read on average negative ~6-10%? (same with long term). Does this indicate a vacuum leak? …a kludgy oxygen sensor? …a dirty MAP? …a combination of any or all?

Topic

[college man]

fuel trims does not seem that bad. Is the front
o2 switching rapidly? When you had the new tires
put on did you have a front end alignment done.
also jack up the car and spins the wheels to make
sure brakes are not dragging.rolling resistance is
everything.

[dreamer2355]

If your LTFT are in the negative, the PCM is taking away fuel.

+1 with the above post. Also check your tire pressures and if the o2 sensor is original, it may warrant replacement.

Do you have access to live PID data?

[lothian]

Yes… via an Actron CP9575

[Steve Webb]

Also don’t discount the possibility of small exhaust leaks especially before the o2 sensors themselves. 🙂

had exactly the same issue and found to be quite substantial manifold leak

[Pete]

I dont mean to steal this thread, but I just had a question along the lines of O2 sensors.

I have a 98 Silverado 1500 and a 04 Aveo LS, both with P0420 codes.

The Silverado has 196,200 miles now, and the Aveo has 142,000. I was wondering if a dirty O2 Sensor could cause the code to show up. The Aveo has it come and go, while the Silverado is on constantly and has it as a Pending Code.

I was wondering if a dirty sensor would do this, because of the fact that it comes and goes on the Aveo. I was told to take out the post-cat O2 Sensors and take some sandpaper to the tip to clean it up and then reinstall. Has anyone done this to fix the code?

[Bill]

Once the slots or holes are plugged with carbon you can’t clean them. I believe that after 100.000 miles O2 sensors start to degrade. I could be full of crap but I really believe it to be true.

Driving a car with lazy O2 sensors are costing you money in lost fuel mileage.

[Pete]

No kidding! I have seen it drop drastically especially in the Aveo. The truck seemed to have the problem since I got it, but wasnt apparent till recently, so I was kinda used to it.

Anyways, you said that they cant be cleaned. What are my changes that changing the post-cat O2 Sensors would get rid of the code? I guess I should ask, how often does a P0420 code mean that the CAT is the problem?

[Bill]

That kinda milage on a 98 GM is a lot to ask from a catalyst. Rather that throw money away on post cat sensors I suggest that you read them with a scan tool that supplies data. They should read steady around .5 volts. If they switch between, say… .2 to .7 volts then the converter is tired out.

On most cars post cat o2 sensors have little effect on fuel mileage. Pre cat sensors do however.

[Pete]

I guess I would need to get a scantool that has live data. The problem is, those are very expensive, and I dont have $100 to throw away. I have a basic one however….

I will see what I can find as far as that. I wish I had a mechanic friend that had a tool like that, so he could get the live data for me.

[Bill]

If there is an Auto Zone close to you they might be able to check that for you.

[Pete]

I just picked up an advanced OBDII Scanner from Harbor Freight Tools ($74.00, but came out to $60 +tax with their 20% off coupon. I even got a free screwdriver set!) that does give live data. I quickly plugged it into the truck and went to the live sensor data, and it was showing the #2 sensors on both sides fluctuating slowly between .4 to .7 volts.

Ill have to play with it more at the house, but I think this is saying that the Cats are bad on this truck.

I stil have to connect it to the Aveo as well.

[Pete]

So I got some video of my O2 Sensors on Live data. I thought id post here and show you all.

Its hard to say what is actually going on, because the O2 Sensors fluctuate alot from time to time. I know the Bank 1s are supposed to do this, but the Bank 2s are supposed to hover around .4 to .7.

Here it is at 2000 RPMs for 1 minute: [video]http://www.youtube.com/watch?v=Vx9Y0Zgz6uA&feature=youtu.be[/video] (http://www. (dot) youtube.com/watch?v=Vx9Y0Zgz6uA&feature=youtu.be)

And here it is for idle: [video]http://www.youtube.com/watch?v=sXEb2Y5x9oo&feature=youtu.be[/video] (http://www (dot) youtube.com/watch?v=sXEb2Y5x9oo&feature=youtu.be)

For some reason, the videos do not show up. Just copy the link in parenthesis and remove the (dot), and replace it with the correct character.

[Author]

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