New to me B8 S4 - horrible MPG and B&O subwoofer issue

[RosSauce]

Last week I bought a higher mileage (~128K mi) 2011 B8 S4. It is completely stock, never modified, and had every service and repair done at the same Audi dealership. After my 1st week of driving I noticed the following:

Scary bad MPG so far. I did a full fill up last Friday and have since drove ~135 miles, mostly city, and it's showing just a smidge over a 1/4 tank left on the fuel gauge. ADS has been in Auto for 85% of this time and I've really only stepped on it maybe 2-3 times going onto highway onramps. The rest of the time was just normal city driving following the flow of traffic. Should I check for vacuum leaks, bad O2 sensor, replace spark plugs and/or fuel filter? Would a carbon cleaning help?
After putting my key into the ignition the other day, I got crazy loud music/static blaring from what sounded like only the rear driver side speaker. Volume controls didn't change it, but luckily I was able to mute it/turn off the MMI. I let it sit overnight and the sound was what I thought back to normal the next day. However, it seems like the B&O sub is barely working now. Before this incident, bass heavy songs would cause the back shelf to rattle a bit with the bass level only turned up a handful of notches past the middle. Now it doesn't do that even with the sub setting turned higher. I can feel the sub vibrating a tiny bit with my hand right next to it but that's about it. Any ideas?

[bandit]

unfortunately your city mpg's sound like par for the course. I cannot comment on your subwoofer issue. Have a shop look at it. GL

[Chris@EPL]

Scan for codes and if you do not know when the plugs and air filter were last replaced you should do both of those.

[RosSauce]

Will do and thanks for the quick help! I had a pre-purchase inspection done at the Audi dealership and other than front control arm bushings going bad, they didn't mention any codes. I'll have to dig through the stack of paperwork to see when the spark plugs were last replaced. I have an appointment to get a front control arm refresh next week at my local indy shop and I plan to ask about my MPG and subwoofer issues to see if they can come up with anything.

I'm hoping to get the EPL stage 1 tune once I get all my maintenance items squared away [up].

[Chris@EPL]

Audi calls for new plugs every 55k miles, but most people do not replace them until there is an issue. LMK when you are ready.

[MrFunk]

What MPG's are you actually getting? Stating you have 1/4 tank left is not very helpful. Perhaps calculate your MPG's over a few fill ups.
With that being said - I've averaged 17mpg over the 9.5 years I've owned the car... it's not a car you buy for stellar MPG.

I've also had that loud static noise from the rear speaker/sub.
Do a full reset on the MMI. It's been probably 5 years now since I had it happen. If you don't know how just google it. Lots of pics and vids.

I'll echo - you should always reset all fluids and maintenance items on a used vehicle, especially with such high miles.
Plugs, filters, all fluids (ALL). Belts?

[whts4]

Early in the ownership of my 2012 s4 (purchaded 3 yrs old)

[whts4]

Early in the ownership of my 2012 s4 (purchaded 3 yrs old)

....purchased when 3 yrs old, had same loud volume ....Audi replaced the amp, which fixed problem.

Mpg in my 2015: city/town is 17-18 mpg, mixed urban driving 21-22, hwy 27-30....over all 22-23...slightly better than the 2012.

[RosSauce]

Thanks for the tips and info. I'll be getting gas tomorrow so I can calculate it based on the capacity filled at the pump. Right now it's looking like 13-14 mpg with 85% city and 15% highway without a lead foot. I definitely drove harder in my MK6 GTI and averaged 23+ mpg and that one had over 170K miles on it. Granted I didn't buy this car for good gas mileage, it just seems to be oddly low.

On the advice given here, I'll plan on doing an oil change, fuel filter change, new spark plugs, control arm refresh, and other fluids as necessary.

[AerotusX]

For reference, I average 17-18mpg (75% highway/25% city) since new for 6 years now. I'm almost always in 'S" + Dynamic mode.

[esimp2k]

My b8 averaged around 15mpg with mostly city driving. I also had the b&o squelch twice. Both times it went away after an mmi reset or the next time starting up the car. There are a handful of threads on it as I recall. Next option would be to unplug the Amp connector and reseat it iirc.


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[RosSauce]

Calculated 14 mpg, hoping after giving it some TLC maintenance at the shop it will improve a bit. Seems to be lower than the majority here but not scary low as I previously stated.

Also, anyone have any idea about the B&O subwoofer issue? Sound is coming fine through all my speakers but the sub isn't producing much "thump" at all. Seems to be working but barely so. Could the amp be going out or possibly a bad connection somewhere? Or can the sub itself go bad?

[Fresh.S4]

Follow the link posted to take the rear shelf apart so you can inspect the oem.
https://m.facebook.com/story/graphql_permalink/?graphql_id=UzpfSTEwMDAwMjM0NzgwNTE1NDpWSzozNDY4OD MwNzYzMjA2NjMw
https://m.facebook.com/story/graphql_permalink/?graphql_id=UzpfSTEwMDAwMjM0NzgwNTE1NDpWSzozNjY4ND IwMDMzMjQ3NzAx

[RosSauce]

Follow the link posted to take the rear shelf apart so you can inspect the oem.
https://m.facebook.com/story/graphql_permalink/?graphql_id=UzpfSTEwMDAwMjM0NzgwNTE1NDpWSzozNDY4OD MwNzYzMjA2NjMw
https://m.facebook.com/story/graphql_permalink/?graphql_id=UzpfSTEwMDAwMjM0NzgwNTE1NDpWSzozNjY4ND IwMDMzMjQ3NzAx

Appreciate the help but the links aren't working. Any chance you can post them again?

[Fresh.S4]

guess you need a fb account.

here is the link to take apart the rear deck. veryyy easy!!
https://www.audiworld.com/forums/s4-b8-platform-discussion-134/b-o-subwoofer-upgrade-install-guide-2790664/?fbclid=IwAR3zfOtI1wjhcYVRIdNC6JDR2rj35TsamFaA13c9 GD2iqh9df6ijXgdIEfQ#&gid=1&pid=14

it also shows how to add an aftermarket subwoofer to help the oem b&o gain some beat back. then the last link the person explained step by step how to add amplifier/ tune it.

[RosSauce]

guess you need a fb account.

here is the link to take apart the rear deck. veryyy easy!!
https://www.audiworld.com/forums/s4-b8-platform-discussion-134/b-o-subwoofer-upgrade-install-guide-2790664/?fbclid=IwAR3zfOtI1wjhcYVRIdNC6JDR2rj35TsamFaA13c9 GD2iqh9df6ijXgdIEfQ#&gid=1&pid=14

it also shows how to add an aftermarket subwoofer to help the oem b&o gain some beat back. then the last link the person explained step by step how to add amplifier/ tune it.

Thanks!

I also went through service records and frustratingly the spark plugs, brake and dsg fluids, some filters, and an oil change were all done in November 2020 so that wouldn't solve my gas mileage issue... doh! Kind of worried about what could be the cause now.

[Starman17]

That’s a pretty normal mpg for how much city you drive. The cars are horrible on slow city roads with lots of stop and go....and you live in SoCal. I’m lucky to get 15 with even higher highway miles...but if I take a road trip almost exclusively on highways I can get 26 to 30 pretty easily.

The fuel gauge is also really conservative... the light comes on for me when I still have a quarter tank left as measured by the fuel pump. I do still wish the tank was a few gallons bigger, though.

[hpclayto]

Thanks!

I also went through service records and frustratingly the spark plugs, brake and dsg fluids, some filters, and an oil change were all done in November 2020 so that wouldn't solve my gas mileage issue... doh! Kind of worried about what could be the cause now.

I don't think you have an issue my friend. Just a big heavy, forced induction AWD vehicle.

[RosSauce]

Thanks for easing my concerns, I tend to over worry on certain things.

[Fresh.S4]

The fuel gauge is also really conservative... the light comes on for me when I still have a quarter tank left as measured by the fuel pump. I do still wish the tank was a few gallons bigger, though.

this.
even when ive taken my fuel level down to like 20miles until empty, i can still manage to only top off with about 14g

[SForePlayin']

Consider using an app like Fuelly or Fuelio (or a pencil and paper) to track it over the next weeks and months to get a better idea of what your MPG is.

[RosSauce]

I also have a burning smell coming from the engine bay that I notice after driving (doesn't enter the cabin) but no notice of leaking that I can find from a quick visual inspection. The coolant was significantly overfilled by the dealer so I siphoned it out to the proper level. However, I've had to add half a quart of oil and about 150+ miles later the oil level is getting close to the minimum level again. Not good. Ugh.

The previous owner had the motor mounts replaced and DSG service done back in November. Could there have been something done with this service that is causing these issues? Or a bad PCV? Hopefully I get some answers Wednesday after taking it into the shop. This makes me not all that trusting of work done at some Audi dealerships.

[Epetes]

In my Touareg I had a camshaft seal leaking oil which dripped directly onto the exhaust and then get cooked and smell, yet never get oil on the floor because it just kept burning off.

Probably not your issue and this is a different engine, but worth looking over exhaust areas to see if any oil leaks are dripping onto exhaust and making the smell.

Sent from my Pixel 3 using Audizine Forum mobile app (http://r.tapatalk.com/byo?rid=87676)

[sacandagaD]

I also have a burning smell coming from the engine bay that I notice after driving (doesn't enter the cabin) but no notice of leaking that I can find from a quick visual inspection. The coolant was significantly overfilled by the dealer so I siphoned it out to the proper level. However, I've had to add half a quart of oil and about 150+ miles later the oil level is getting close to the minimum level again. Not good. Ugh.

The previous owner had the motor mounts replaced and DSG service done back in November. Could there have been something done with this service that is causing these issues? Or a bad PCV? Hopefully I get some answers Wednesday after taking it into the shop. This makes me not all that trusting of work done at some Audi dealerships.

That kind of oil consumption combined with the age of the engine, would lend one to believe it is a PCV issue. If so, there's a whole laundry list of things you should do while you are at it, including Carbon Cleaning and T-stat.