Gas Mileage (25-27 HWY & 14-16 City)

[AudiTurbo]

So, I know this has been talked about a lot, but I can't figure out my problems in the city. My mods are listed below and I don't have any cel. It's like if I park with a 1/4 tank and when I come back out it's under 1/4. I don't think its a leak, but could be.

New plug, new filter, new oil, new fuel filter.
Can I have a bad MAF or o2 sensor without a code showing up causing bad gas mileage? Could it be that I am running pc-16 without a front mount and it's running rich?

Thanks!

[RoadRage]

Do you drive hard? Those numbers don't seem uncommon. and you could give the MAF a cleaning and see if it helps.

[seanj130]

If you highway MPG was lower I would suggest a bad O2 sensor. Is you CEL bulb burnt out? Check to see if you have any codes.

So, I know this has been talked about a lot, but I can't figure out my problems in the city. My mods are listed below and I don't have any cel. It's like if I park with a 1/4 tank and when I come back out it's under 1/4. I don't think its a leak, but could be.

New plug, new filter, new oil, new fuel filter.
Can I have a bad MAF or o2 sensor without a code showing up causing bad gas mileage? Could it be that I am running pc-16 without a front mount and it's running rich?

Thanks!

[AudiTurbo]

I don't drive it hard at all. The light is not broken, but when I scan it sometimes it will throw the code for the rear o2 sensor. Can a sensor be bad and not throwing a code?
I noticed a lot of oil on my plug (need valve cover gasket change) Could that be a problem and if it is how can I get the oil out of there?

[gregory.fazekas]

First replace the rear 02 sensor. While a tune makes it so you won't throw a cat efficiency code with your test pipe, it still has to deal with fuel economy and can foul once you install a test pipe. After that, I would fix the gasket so your car doesn't get oil on the plugs to make a more complete burn. Replace the plugs with copper plugs and give the engine a good sea foaming before you replace the plugs.

[SN95Audi87]

I read a thread on here saying that a rear o2 sensor can play a role in mpg. I would look into that if the front one has been replaced before. I replaced my front but not the back yet. My mpg is ok, but not the best.

[AudiTurbo]

Okay thank you all. I just got a universal o2 sensor, so I'll need to splice the wires. The code it was throwing was 16522 (p0138 o2 sensor circuit, bank 1-sensor 2: high voltage)

[RoadRage]

Okay thank you all. I just got a universal o2 sensor, so I'll need to splice the wires. The code it was throwing was 16522 (p0138 o2 sensor circuit, bank 1-sensor 2: high voltage)

replace that sensor and see if things improve. FYI you can google the code to find out more info, FOR EXAMPLE