Poor fuel economy?

[Thewheelm4n]

Hey guys, curious if anyone may have any ideas and solutions to poor fuel economy I've been getting over the last several weeks. I drive for a living, probably 70% city driving, and usually average in the range of 26.5-28mpg. Lately, it's been down in the 22-24mpg range and I have zero ideas as to why. Just put new all seasons on it less than a week ago, replaced plugs with NGK Iridium's less than 7k miles ago, car runs fine, just seems to have tanked in economy. The only issue is an intermittent bank 1 sensor 1 o2 code that pops up every once and a while and throws a CEL, but it goes away after driving 30mi or so and then doesn't come back for weeks. Car isn't consuming a drop of oil since I replaced the PCV. Thoughts?

Stock 2015 S3

[MikTip]

Hey guys, curious if anyone may have any ideas and solutions to poor fuel economy I've been getting over the last several weeks. I drive for a living, probably 70% city driving, and usually average in the range of 26.5-28mpg. Lately, it's been down in the 22-24mpg range and I have zero ideas as to why. Just put new all seasons on it less than a week ago, replaced plugs with NGK Iridium's less than 7k miles ago, car runs fine, just seems to have tanked in economy. The only issue is an intermittent bank 1 sensor 1 o2 code that pops up every once and a while and throws a CEL, but it goes away after driving 30mi or so and then doesn't come back for weeks. Car isn't consuming a drop of oil since I replaced the PCV. Thoughts?

Stock 2015 S3

You answered your own question...

intermittent bank 1 sensor 1 o2 code that pops up

02 sensors can effect fuel economy...

[Thewheelm4n]

You answered your own question...

intermittent bank 1 sensor 1 o2 code that pops up

02 sensors can effect fuel economy...

Ahh, wasn't sure on that but it was my only hypothesis.

Just to be sure, that's this sensor, correct? https://www.fcpeuro.com/products/aud...2d#description

[Thewheelm4n]

And it's the one located up by the top rear of the engine, correct?

[MikTip]

Rockauto.com

Sells the Denso 02 sensor for $149...

https://www.rockauto.com/en/catalog/...2)+sensor,5132

IMO the Denso 02 is better than the OE Bosch.

[Thewheelm4n]

Rockauto.com

Sells the Denso 02 sensor for $149...

https://www.rockauto.com/en/catalog/...2)+sensor,5132

IMO the Denso 02 is better than the OE Bosch.

Really? Interesting. Well, the reason I sent the fcp link for the OEM is their lifetime warranty; if I buy the sensor through them, even though it's more out of pocket initially, in the end I can send back the faulty sensor and I'll basically only be paying tax and return shipping. That lifetime warranty refund policy has saved my butt more times than I can count financially over the years.

[MikTip]

Really? Interesting. Well, the reason I sent the fcp link for the OEM is their lifetime warranty; if I buy the sensor through them, even though it's more out of pocket initially, in the end I can send back the faulty sensor and I'll basically only be paying tax and return shipping. That lifetime warranty refund policy has saved my butt more times than I can count financially over the years.

Where ever you want to spend your money...feel free!

[Thewheelm4n]

Could a slit in the hose connecting the PCV to the purge valve cause an intermittent o2 sensor code and poor fuel economy? When I swapped out the PCV a couple months back, I noticed near the part of the little hose (https://www.ecstuning.com/b-genuine-...se/06l133514a/) where it slips over the nipple on the purge valve had a slit in it. Couldn't tell if it was cut deep enough to affect vacuum, but a local shop I trust said it should be my starting point as it's a much cheaper fix than replacing the o2 and could definitely be causing my issues.

Thoughts?

[Thewheelm4n]

Also, would I need to go to the dealer to have them flash updated software for the new PCV Valve since it's an updated design from the one I took out? Was told this also might be needed. Thanks again.

[MikTip]

Also, would I need to go to the dealer to have them flash updated software for the new PCV Valve since it's an updated design from the one I took out? Was told this also might be needed. Thanks again.

Updated design PVC? First I have heard of it...

The PVC...AKA oil separator simply tries to seperate the oil fumes from the air...but it mainly allows the engine to suck into the intake the oil fumes.

Which make it to the intake valves and carbon coat the intake valves.

I doubt the ECU needs software update for the PVC which totally runs on vacuum...

Maybe if your year Audi has a MAF sensor...since it measures intake air...

[MikTip]

I see the 2022 Audi S3 motor has a different looking PVC...not sure it if works/fits onto the older models...

[Thewheelm4n]

I see the 2022 Audi S3 motor has a different looking PVC...not sure it if works/fits onto the older models...

Mines year one, 2015. What I meant by updated design was just superceded part #. Seems they've released many revisions of the PCV valve. Seemed odd to me it'd need a software update too, figured I'd ask.

Do you think that hose being cut could cause my fuel economy issues and that intermittent o2 code? Replacing that hose would be a lot cheaper than the o2 so I'd like to start there if it makes sense.

[MikTip]

Mines year one, 2015. What I meant by updated design was just superceded part #. Seems they've released many revisions of the PCV valve. Seemed odd to me it'd need a software update too, figured I'd ask.

Do you think that hose being cut could cause my fuel economy issues and that intermittent o2 code? Replacing that hose would be a lot cheaper than the o2 so I'd like to start there if it makes sense.

If your 2015 S3 has a MAF sensor in the intake...I would say yes. No MAF I'd say no...
For me the CEL pointing to the 02 would be good reason to change it....especially if its an original 2015. Any mods on the car? Tunes?

[Thewheelm4n]

If your 2015 S3 has a MAF sensor in the intake...I would say yes. No MAF I'd say no...
For me the CEL pointing to the 02 would be good reason to change it....especially if its an original 2015. Any mods on the car? Tunes?

I'll have to look and see if it's got a MAF. My local VW/Audi shop I go to for work I can't do myself saw the code and said replace the o2, I've been getting it intermittently for months but haven't seen fuel economy issues til the last couple weeks. CEL will come on every once and a while while driving and then go away on its own, sometimes I'll get a hard start once, try starting again and it'll stutter, fire up and throw the CEL, then I'll go weeks without it popping up again. Car does kinda "stutter" a little at idle generally most of the time, this went away almost completely after I initially replaced the PCV but it's been back now again for a bit. NGK Iridiums replaced less than 10k ago.

[Thewheelm4n]

If your 2015 S3 has a MAF sensor in the intake...I would say yes. No MAF I'd say no...
For me the CEL pointing to the 02 would be good reason to change it....especially if its an original 2015. Any mods on the car? Tunes?

And sorry, no mods at all, car is completely stock.

[Thewheelm4n]

If your 2015 S3 has a MAF sensor in the intake...I would say yes. No MAF I'd say no...
For me the CEL pointing to the 02 would be good reason to change it....especially if its an original 2015. Any mods on the car? Tunes?

20221002_142942.jpg

Doesn't look like there's a MAF.

[MikTip]

20221002_142942.jpg

Doesn't look like there's a MAF.

Something ya might want to consider...carbon cleaning the intake valves.

[Thewheelm4n]

Something ya might want to consider...carbon cleaning the intake valves.

I had planned on that, the shop I go to doesn't do carbon cleanings and says additives like Chevron Techron are good enough, idk how I feel about that. Would have to find a local shop that'd do it. Car has about 157k on it so I'd assume Carbon buildup is probably significant, our fuel in NYS sucks.

[MikTip]

I had planned on that, the shop I go to doesn't do carbon cleanings and says additives like Chevron Techron are good enough, idk how I feel about that. Would have to find a local shop that'd do it. Car has about 157k on it so I'd assume Carbon buildup is probably significant, our fuel in NYS sucks.

Well...that shop is clueless about your Audi's direct injection system...

Mine at 160,000 had pretty significant carbon build up...

Carbon build up isn't caused from the fuel...its caused from the oil fumes the PVC directs into the engine at the turbo inlet pipe.

[Thewheelm4n]

Well...that shop is clueless about your Audi's direct injection system...

Mine at 160,000 had pretty significant carbon build up...

Carbon build up isn't caused from the fuel...its caused from the oil fumes the PVC directs into the engine at the turbo inlet pipe.

Yeah, I just know fuel can cause engine deposits as well, that's why I mentioned it. What's a good price you think a shop should charge for carbon cleaning? Walnut blasting the most reliable method? Back when I had BMWs a couple shops locally charged in the $400 range.

[Thewheelm4n]

Well...that shop is clueless about your Audi's direct injection system...

Mine at 160,000 had pretty significant carbon build up...

Carbon build up isn't caused from the fuel...its caused from the oil fumes the PVC directs into the engine at the turbo inlet pipe.

Well, had Autobahn Centre here perform their 3 stage carbon cleaning and swapped in a new PCV-to-purge valve rubber hose, still getting poor fuel economy, had a hard start today and the same bank 1 sensor 1 o2 code came back again.

[MikTip]

Well, had Autobahn Centre here perform their 3 stage carbon cleaning and swapped in a new PCV-to-purge valve rubber hose, still getting poor fuel economy, had a hard start today and the same bank 1 sensor 1 o2 code came back again.

So you still haven't changed the 02 sensor for which the CEL repeatedly comes on for?

[Thewheelm4n]

So you still haven't changed the 02 sensor for which the CEL repeatedly comes on for?

Multiple shops have told me it could be being mimicked by vacuum leak, carbon buildup, bad injector, bad fuel, so trying to rule out other cheaper, easier options first. Assuming at this point it probably is the o2 that's bad, just wanted to update for any other ideas here before going that route.

[Thewheelm4n]

So you still haven't changed the 02 sensor for which the CEL repeatedly comes on for?

Well, the plot thickens. I got a new code today:

O2 sensor signal stucco lean; bank 1 sensor 2


This is now in addition to the persistent code "o2 sensor negative current control circuit bank 1 sensor 1 open" I've had coming on and off since May, and two additional codes that show up every once and a while:

System too rich at idle, bank 1
Cyl. 2 misfire detected

Thoughts?

[ReggieNoble]

Well, the plot thickens. I got a new code today:

O2 sensor signal stucco lean; bank 1 sensor 2


This is now in addition to the persistent code "o2 sensor negative current control circuit bank 1 sensor 1 open" I've had coming on and off since May, and two additional codes that show up every once and a while:

System too rich at idle, bank 1
Cyl. 2 misfire detected

Thoughts?

Well if you have a tire light come on, then you add air right? You don't start checking the lug bolts and center caps. If you have a O2 sensor code, then you replace the O2 sensor. In the aspect of car repairs they are one of the cheapest things you can do, and they should be replaced every few years regardless of condition. So quit beating a dead horse and replace it. Then if the codes come back, you know you eliminated the most obvious choice.

[MikTip]

Well if you have a tire light come on, then you add air right? You don't start checking the lug bolts and center caps. If you have a O2 sensor code, then you replace the O2 sensor. In the aspect of car repairs they are one of the cheapest things you can do, and they should be replaced every few years regardless of condition. So quit beating a dead horse and replace it. Then if the codes come back, you know you eliminated the most obvious choice.

...

[Thewheelm4n]

Well if you have a tire light come on, then you add air right? You don't start checking the lug bolts and center caps. If you have a O2 sensor code, then you replace the O2 sensor. In the aspect of car repairs they are one of the cheapest things you can do, and they should be replaced every few years regardless of condition. So quit beating a dead horse and replace it. Then if the codes come back, you know you eliminated the most obvious choice.

My point was, I have tried to eliminate easier/cheaper possible causes but kept getting the same code, so I was going to order the bank 1 sensor 1 o2, but then randomly I get those two codes that seem to negate that idea, a sensor 2 lean code, when the whole time it's been sensor 1/rich situation. I don't want to go blow $400+ on two new o2 sensors if there's some other explanation (I. E. How can there be a rich and lean condition simultaneously?), like a faulty injector or ignition coil. Am I wrong in trying to be cautious and not just throw parts at it here?

[Thewheelm4n]

I'm now getting several misfire codes. Starting to think it may be faulty ignition coils as the car does have 160k on it now. Thoughts?Screenshot_20221101-202209.jpgScreenshot_20221101-202203.jpgScreenshot_20221101-202157.jpg

[Thewheelm4n]

So, 169k now, I've replaced the ignition coils with APR upgraded coils and I just replaced the upstream (bank 1 sensor 1) o2 yesterday that kept throwing the same code over and over. Fuel economy seems marginally improved but not as much as I expected, and the hard start condition happened again today. I don't have any engine related codes other than one about a coolant valve (which obviously wouldn't cause any of these issues), not sure where to go from here. I did get a few misfire codes before I swapped out the coils, but since then they haven't returned. The car has always had a slightly rough idle, I'd hoped that'd go away replacing the o2 but it's still there as well. Local euro shop posited that injectors may need replacing (said could cause the hard start/misfire codes/rough idle), I'm betting they're original and with 169k on it now that'd make sense, but I've never gotten any specific injector codes. I did once get a code referencing the downstream o2, but it's never reoccurred, the upstream was there constantly since 132k miles. Thoughts?

[ReggieNoble]

So, 169k now, I've replaced the ignition coils with APR upgraded coils and I just replaced the upstream (bank 1 sensor 1) o2 yesterday that kept throwing the same code over and over. Fuel economy seems marginally improved but not as much as I expected, and the hard start condition happened again today. I don't have any engine related codes other than one about a coolant valve (which obviously wouldn't cause any of these issues), not sure where to go from here. I did get a few misfire codes before I swapped out the coils, but since then they haven't returned. The car has always had a slightly rough idle, I'd hoped that'd go away replacing the o2 but it's still there as well. Local euro shop posited that injectors may need replacing (said could cause the hard start/misfire codes/rough idle), I'm betting they're original and with 169k on it now that'd make sense, but I've never gotten any specific injector codes. I did once get a code referencing the downstream o2, but it's never reoccurred, the upstream was there constantly since 132k miles. Thoughts?

If you haven't done it yet, change out the oil separator/ pcv and N80, helped my idle tremendously. Another possibility that causes hard starts and misfires wth no codes it's the cam magnet adjusters. They are super easy to replace and from my experience it's usually the intake side that causes issues for some reason.

[Thewheelm4n]

Scratch that, just did a scan after a very lengthy hard start and indeed the misfire codes have returned. Screenshot_20221230-164300.jpgScreenshot_20221230-164306.jpgScreenshot_20221230-164254.jpgScreenshot_20221230-164241.jpg

[Thewheelm4n]

If you haven't done it yet, change out the oil separator/ pcv and N80, helped my idle tremendously. Another possibility that causes hard starts and misfires wth no codes it's the cam magnet adjusters. They are super easy to replace and from my experience it's usually the intake side that causes issues for some reason.

I did do the PCV valve and breather hose maybe 15-20k ago, it initially helped a lot with the rough idle (and completely cured my oil consumption). What is the N80? And do you have part #s/Pic locations for the cam magnet adjusters? Thanks!

[Rod Paine]

Our 2019 Audi RS 3 is now at 43,075 miles of which 31,014 miles have been fast country back
road runs 3 days a week (tues,weds, thurs) only between 10am and 2 pm as weather permits
and these roads are usually pretty much empty at this time of day. Weekend drives is a NO-NO
given all the idiots on these roads during the weekends.

Our Audi is garaged that is heated at 65°F automatically and is heavily insulated to insure
that rust of my many dollars of tools that have been collected since 1957, is not an issue.
We're 55 miles west of Washington DC and weather can get pretty cold here, so the Audi
is certainly in a very good enviorment, fortunately.

[Thewheelm4n]

Our 2019 Audi RS 3 is now at 43,075 miles of which 31,014 miles have been fast country back
road runs 3 days a week (tues,weds, thurs) only between 10am and 2 pm as weather permits
and these roads are usually pretty much empty at this time of day. Weekend drives is a NO-NO
given all the idiots on these roads during the weekends.

Our Audi is garaged that is heated at 65°F automatically and is heavily insulated to insure
that rust of my many dollars of tools that have been collected since 1957, is not an issue.
We're 55 miles west of Washington DC and weather can get pretty cold here, so the Audi
is certainly in a very good enviorment, fortunately.

Uh... What does this have to do with the subject being discussed here? Thanks?

[Thewheelm4n]

Bump.

[Rod Paine]

Our fuel mileage is 28.3 MPG over the past 43, 257 miles of which 31,165
has been a total of our country fast back road weekly runs to date.

[Thewheelm4n]

Can someone reply regarding my issues please?

[CXSnail]

O2 sensors degrade with age and miles. Slower to update, inaccurate, etc.

It's been mentioned a couple times that you need to swap those, and I'll echo that. Start simple.

I have read other threads about people fixing odd startup misfires with hpfp and injector replacements, but it's foolish to jump to those conclusions without knowing you have an accurate fuel metering feedback (the air fuel/O2 sensors).

[CXSnail]

Also you asked above how can an O2 report rich and lean at the same time? Easy. If it's failing, it can drift rich and hang there, then another minute drift lean and stay there. Meanwhile fuel trims are trying to compensate for an "issue" that isn't there. Just an air fuel sensor that's lying to you.

[CXSnail]

Nevermind, I saw in your other thread about this same issue that you did in fact replace the sensor. Not sure how I missed that here.

Anyway, considering the issue really can't be logged and shared here without some sort of device like the Cobb accessport, you'll have to resort to shotgunning parts still. There are a number of things that can fail at this mileage, nobody is going to have a direct answer, unfortunately.