o2 sensor and bad MPGs

[miggity02]

I was wondering if o2 sensors have a great impact with MPGs (~3-4mpg) Could they also be related to engine pinging below 3000 rpm or is that a fuel pump issue? Also, which o2 sensor is the more important one, front or back? Any good deals out there for o2 sensors?

[MikTip]

Sounds more like bad gas....

Throw in a bottle of Techron!

[dirtybrd]

Frt. o2 is the one for fueling.

[downhillracer]

if the o2 was bad you would have an 02 code...

[msharifi]

I was wondering if o2 sensors have a great impact with MPGs (~3-4mpg) Could they also be related to engine pinging below 3000 rpm or is that a fuel pump issue? Also, which o2 sensor is the more important one, front or back? Any good deals out there for o2 sensors?

How many miles on your car? Here is my story.. My 1.8t AWD had 66k and my mpg was really bad. I could see the mpg on the screen go up and down. I scan for codes but nothing about 1st o2 sensor which effects your MPG. I read online that o2 sensors get lazy but yet does not give you a bad code. I ordered a new o2 sensor from mjm. I installed it and noticed the difference. Also how often do you change your oil? I'm changing it every 5K which helps you a lot too.

[miggity02]

MSHARIFI:
I change my oil every 5-6k miles with Valvolinve or Syntec 5w-30. I have about 90k miles. I've scanned for codes too and nothing's come up. Maybe I'll change the o2 sensor and see if it helps. You said the first one correct? The one you can see in the engine bay? (I know, stupid question) I've heard good things about MJM, have you had a good experience with them?

[msharifi]

MSHARIFI:
I change my oil every 5-6k miles with Valvolinve or Syntec 5w-30. I have about 90k miles. I've scanned for codes too and nothing's come up. Maybe I'll change the o2 sensor and see if it helps. You said the first one correct? The one you can see in the engine bay? (I know, stupid question) I've heard good things about MJM, have you had a good experience with them?

Audi uses Castrol 5w-40 and 0w-40 Mobil 1. Audi Dealers use Castrol 5w-40. Everyone is different on their oil changes :) We have turbos in our car which the wrong oil grade can affect the Turbo which shares oil.

The first O2 which you can see from the engine bay next to the airbox.

I did order mine from MJM they sell the same part that Audi sells it. I checked with Audi dealer and they quoted me $250. I got it from MJM for $120 no sales tax and free shipping.

I have 66K and my second O2 sensor after the CAT is bad and I'm going to order that from MJM and install it because if my CAT is bad I can't tell since the O2 sensor is bad and Audi has it warranty for 8 years or 80K miles.

Good luck

[Peter@VMRWheels]

O2 Sensor, Plugs, Coils ... the list is pretty long for this kind of stuff :)

[msharifi]

True but I have heard that the O2 sensor gets lazy... Sounds funny but when I changed mine better MPG.

[miggity02]

Maybe I'll do 5w-40 or 0w-40 next time I change my oil. I live in the SF Bay Area so temps don't really get too cold here. I think I've seen more 0w-40 Mobil 1 than the 5w-40 Castrol, so I'll try 0w-40 first. I changed coils and plugs about 6 months ago and I put a K&N drop in about 4 months ago. I think a "lazy" sensor could be the problem. I'm getting ~275 miles per tank with 11-12 gallon fill up, Chevron 91 or 76 91, mostly highway driving. Is that what you guys are seeing?

[msharifi]

Maybe I'll do 5w-40 or 0w-40 next time I change my oil. I live in the SF Bay Area so temps don't really get too cold here. I think I've seen more 0w-40 Mobil 1 than the 5w-40 Castrol, so I'll try 0w-40 first. I changed coils and plugs about 6 months ago and I put a K&N drop in about 4 months ago. I think a "lazy" sensor could be the problem. I'm getting ~275 miles per tank with 11-12 gallon fill up, Chevron 91 or 76 91, mostly highway driving. Is that what you guys are seeing?

I used to put 0w-40 until I went to the dealer to get the filter and I asked how much the oil was and he showed me the Castrol 5w-40 and he said this what Audi uses it on all A4s and some others.

I heard the K&N filter is bad for our turbos because it has some kind of oil on the filter that can damage your Turbo.

Is 275 Miles per tank freeway or stop and go? Also is yours a FWD or AWD? mine is AWD I get a little better on stop and go with the new Sensor and oil change. Freeway is the best I can go from Irvine to SD on a fill up and by the time I'm in SD very little gas is used. I can pull 480 Miles per tank on freeway and about 250-260 on stop and go.

Other factors can effect your MPG..

1. Dirty Air filter
2. Tire PSI set incorrect
3. Bad Alignment
4. Cold weather
5. Too many stop and goes
6. To many miles on Spark plug or new spark plug gab is not set correctly
7. Last thing depends on how heavy your right foot is when you press on the gas at a stop and go :)

I used to have a Cold Air intake and I took it out since the OEM one is much better. I try to put Shell 91 because you can't beat the best gas out there.

[dirtybrd]

if the o2 was bad you would have an 02 code...

Not necessarily

[msharifi]

If it gets really bad yes but not most of the time.

[miggity02]

The 275 miles is mostly highway on a Quattro. I also have a Revo Stage 1 chip. Now I'm assuming that a chip itself will not lower gas mileage 200 miles per tank. I don't drive hard, especially when I am commuting. I keep my tires between 38-40 PSI and my alignment is fine. At the beginning I thought maybe the chip had something to do with it, but I had the shop check it out and they ran a check and revealed nothing wrong. The K&N was recommended to me by my performance shop and they are pretty reliable and honest when it comes to mods. All of the employees including the owner uses it too, so I figured it was OK. I've used them in other cars as well and had no problems with it.

[dougyfresh]

True but I have heard that the O2 sensor gets lazy... Sounds funny but when I changed mine better MPG.

O2s are lazy when they go out. Front one (primary) is a wide-band and feeds air/fuel info to the ECu to the ECu can adjust the fuel trims accordingly.

My primary O2 just died. Its been lazy where some days it works perfectly fine and I get great gas mileage and the car runs strong. Other days it throws an O2 CEL and the car gets horrible gas mileage.

My new primary O2 should arrive this week. I bought it from autohausaz.com

My primary O2 has 134k on it. It is recommended to replace every 100k.

Have you ever gotten a CEL? If not, then I do not think your O2 sensor is on the fritz.

[miggity02]

No CEL...yet...