Decreased MPG

e46e92love · 08-16-2016, 08:32 AM

Just wondering if anyone knows of anything specific a significant decline in mpg could indicate?

My thoughts were SP or carbon build up but I use She'll V and have since she was born.

No increased oil burn or loss of power (according to my butt dyno ?) or anything of the sorts. Driving habits the same. Don't care about the decreased MPG as long as it's not an indication of something it needs such as SP.

Thanks in advanced guys / gals.

Cheers,
e46e92

Get lit · 08-16-2016, 09:28 AM

how much has it dropped?? How much is significant? Hotter weather temps and running a/c constantly can cause a decline in mpg. Usually only by a small amount though. Dirty air intake filters and fouled spark plugs are another simple cause.

roastbeef · 08-16-2016, 09:58 AM

What's your mileage? When was last time the spark plugs were changed?

e46e92love · 08-16-2016, 10:48 AM

Quote:

Originally Posted by roastbeef

What's your mileage? When was last time the spark plugs were changed?

Mileage is 60k and I think 30k was when they were done although I'm at work and don't know for sure.

I do know about 2k ago car said "change my plugs in 10k". I had planned on doing them in Sept before fall track season, but just want to make sure it's no more than the usual.

As far as decease, 2mpg less.....after 5+ years of ownership (she a March 2011 build) have never seen such a drastic decrease so ruled out hot weather / AC although I will say this summer has been one of the hotter / more humid ones than the last two.

Thanks guys, will replace filters and plugs in two weeks and see if that changes anything. Again, not concerned, just want to make sure it's not a sign that she needs me to do something else.

Cheers,
e46e92

CognitiveDistortion · 08-16-2016, 11:05 AM

If you are doing anything like this, I would guess it would also affect your MPG:

[u2b]

[/u2b]

dparm · 08-16-2016, 11:06 AM

Quote:

Originally Posted by e46e92love

Just wondering if anyone knows of anything specific a significant decline in mpg could indicate?

My thoughts were SP or carbon build up but I use She'll V and have since she was born.

No increased oil burn or loss of power (according to my butt dyno ?) or anything of the sorts. Driving habits the same. Don't care about the decreased MPG as long as it's not an indication of something it needs such as SP.

Thanks in advanced guys / gals.

Cheers,
e46e92

Could be a lot of things. In theory, anything that controls or influences air/fuel/spark can negatively impact fuel economy. Example: a flaky oxygen sensor might send incorrect data back to the ECU, which in turn causes a rich mixture. Hell, it could be something stupid like a tire being 1 or 2psi low (well outside the realm of TPMS alerting you).

If the car is up to date on maintenance I would continue to monitor for a few more tanks of gas and make sure it isn't just a fluke due to increased AC usage, a different driving pattern (e.g. is your primary commute under construction which leads to more stop-and-go), etc. You could also buy a code reader such as Carly and see if there are any non-critical fault codes stored that are pointing to intermittent problems.

2mpg isn't really that significant in my opinion.

Amirsm3 · 08-16-2016, 11:19 AM

There isn't a specific mileage for spark plugs in the iDrive service menu, IIRC. You're due for spark plugs, IMO. Get those done, check your air filter and call it a day haha.

dparm · 08-16-2016, 11:32 AM

Quote:

Originally Posted by Amirsm3

There isn't a specific mileage for spark plugs in the iDrive service menu, IIRC. You're due for spark plugs, IMO. Get those done, check your air filter and call it a day haha.

Correct, the CBS readout doesn't show plugs. The interval is every 37k miles/60k KM.

nachob · 08-16-2016, 03:45 PM

Oxygen sensor is a
Common culprit but would throw engine light. When ox sensors fail they default to richer mixture.

roastbeef · 08-16-2016, 05:32 PM

Quote:

Originally Posted by Amirsm3

There isn't a specific mileage for spark plugs in the iDrive service menu, IIRC. You're due for spark plugs, IMO. Get those done, check your air filter and call it a day haha.

yea.... the car will never ask for spark plugs, they aren't part of the cbs. manual says 37k for plugs.

AaronJ47 · 08-16-2016, 11:47 PM

What MPG are you getting on average?

08-16-2016, 08:32 AM	#1
e46e92love Brigadier General 236 Rep 3,303 Posts Drives: e92 ///M3; X3 (wife's) Join Date: Nov 2007 Location: The East Side of Things iTrader: (0)	Decreased MPG Just wondering if anyone knows of anything specific a significant decline in mpg could indicate? My thoughts were SP or carbon build up but I use She'll V and have since she was born. No increased oil burn or loss of power (according to my butt dyno ?) or anything of the sorts. Driving habits the same. Don't care about the decreased MPG as long as it's not an indication of something it needs such as SP. Thanks in advanced guys / gals. Cheers, e46e92 __________________ "...it's not about the money and not about the brand of the car, it's about handling,performance and passion......And that, no other car has all together like an M3........when you talk about the most complete car the M is invincible." --Tony Kanaan.
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08-16-2016, 09:28 AM	#2
Get lit HMFIC 372 Rep 522 Posts Drives: 2016 F80 M3 Join Date: Oct 2014 Location: Charleston SC iTrader: (1) Garage List 2016 BMW M3 [0.00]	how much has it dropped?? How much is significant? Hotter weather temps and running a/c constantly can cause a decline in mpg. Usually only by a small amount though. Dirty air intake filters and fouled spark plugs are another simple cause.
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08-16-2016, 09:58 AM	#3
roastbeef Lieutenant General 11585 Rep 12,724 Posts Drives: E92 M3 Join Date: Nov 2010 Location: Orange County, CA iTrader: (4)	What's your mileage? When was last time the spark plugs were changed? __________________ Instagram; @roastbeefmike
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08-16-2016, 11:05 AM	#5
CognitiveDistortion Second Lieutenant 65 Rep 242 Posts Drives: M3 Join Date: May 2014 Location: Atlanta, GA iTrader: (0)	If you are doing anything like this, I would guess it would also affect your MPG: [u2b] [/u2b]
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08-16-2016, 11:19 AM	#7
Amirsm3 Brigadier General 514 Rep 3,482 Posts Drives: 2011 Space Grey e90 M3 Join Date: Feb 2014 Location: Williams/Flagstaff, AZ iTrader: (3)	There isn't a specific mileage for spark plugs in the iDrive service menu, IIRC. You're due for spark plugs, IMO. Get those done, check your air filter and call it a day haha. __________________ 2011 e90 M3 Space Grey DCT ZCP- eAs, BMW Performance, Agency Power, Macht Schnell, iND, Milltek, Volk, Challenge, Stoptech, Ohlins BMWCCA:518970
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08-16-2016, 03:45 PM	#9
nachob Brigadier General 2314 Rep 4,341 Posts Drives: 2004 330i ZHP, 2022 Cayman T Join Date: Apr 2008 Location: California iTrader: (5)	Oxygen sensor is a Common culprit but would throw engine light. When ox sensors fail they default to richer mixture.
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08-16-2016, 11:47 PM	#11
AaronJ47 Private First Class 32 Rep 139 Posts Drives: E90 M3, Ford Cosworth, FPV F6 Join Date: May 2015 Location: Vancouver, WA iTrader: (0)	What MPG are you getting on average?
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