Fuel economy just went down dramatically--ideas?

CombatNinja · 03-03-2012, 03:17 PM

Got the oil changed the week before last under free maint. program and since doing so my MPG is 1.8-2mpg worse. This is on a 2009 auto 328i with just under 30K on it. The mpg is verified by actual calculations and confirmed by the car's computer. I used to see 22.3-22.6 consistently over tanks and it is suddenly down to 20.0-20.5. No change in driving habits. routes, traffic or load in the car. It is of course getting warmer but it is certainly not hot outside by any means. Tire pressures are spot on. My only thought is that perhaps my area just went away from winter blend gasolines and that is causing the issue? Any ideas?

Hooy · 03-03-2012, 04:47 PM

Clean MAF sensor

funnyface · 03-08-2012, 01:38 AM

Winter blend usually decreases your MPG so that shouldn't be it.

They might have used a heavier weight oil like 0w-40 instead of 5w-30.

I would just change the air filter (you have to pull the airbox out anyway if you're going to clean the MAF sensor) and look at changing the spark plugs depending on your mileage.

CombatNinja · 03-08-2012, 05:38 AM

Update: Just fueled up yesterday and calculated 22.8 mpg for that tank. But all is not well as I'm sure that I was driving more gently trying to "fix" the mpg issue. I used to get 22.X driving around in "DS" all the time.

CombatNinja · 03-09-2012, 07:16 AM

The 2011 that my wife has been driving was showing 20.X on the computer when I got in (no wonder she has so many tickets

). I reset and took the car for the day and eked out 29.8mpg. Granted this is a sedan vs a wagon and non sport vs sport but that is a huge difference. I think the e91 is sick.

03-03-2012, 03:17 PM	#1
CombatNinja Banned 46 Rep 1,556 Posts Drives: e91 328i, e90 328i, e90 335i Join Date: Feb 2011 Location: United States iTrader: (0)	Fuel economy just went down dramatically--ideas? Got the oil changed the week before last under free maint. program and since doing so my MPG is 1.8-2mpg worse. This is on a 2009 auto 328i with just under 30K on it. The mpg is verified by actual calculations and confirmed by the car's computer. I used to see 22.3-22.6 consistently over tanks and it is suddenly down to 20.0-20.5. No change in driving habits. routes, traffic or load in the car. It is of course getting warmer but it is certainly not hot outside by any means. Tire pressures are spot on. My only thought is that perhaps my area just went away from winter blend gasolines and that is causing the issue? Any ideas?
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03-03-2012, 04:47 PM	#2
Hooy Colonel 205 Rep 2,770 Posts Drives: E92 328i, E92 M3 Join Date: Sep 2009 Location: Houston, TX iTrader: (12) Garage List 2008 E92 328 [5.00]	Clean MAF sensor __________________
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03-08-2012, 01:38 AM	#3
funnyface New Member 0 Rep 5 Posts Drives: e92 Join Date: Feb 2012 Location: Chicago iTrader: (0)	Winter blend usually decreases your MPG so that shouldn't be it. They might have used a heavier weight oil like 0w-40 instead of 5w-30. I would just change the air filter (you have to pull the airbox out anyway if you're going to clean the MAF sensor) and look at changing the spark plugs depending on your mileage.
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03-08-2012, 05:38 AM	#4
CombatNinja Banned 46 Rep 1,556 Posts Drives: e91 328i, e90 328i, e90 335i Join Date: Feb 2011 Location: United States iTrader: (0)	Update: Just fueled up yesterday and calculated 22.8 mpg for that tank. But all is not well as I'm sure that I was driving more gently trying to "fix" the mpg issue. I used to get 22.X driving around in "DS" all the time.
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03-09-2012, 07:16 AM	#5
CombatNinja Banned 46 Rep 1,556 Posts Drives: e91 328i, e90 328i, e90 335i Join Date: Feb 2011 Location: United States iTrader: (0)	The 2011 that my wife has been driving was showing 20.X on the computer when I got in (no wonder she has so many tickets ). I reset and took the car for the day and eked out 29.8mpg. Granted this is a sedan vs a wagon and non sport vs sport but that is a huge difference. I think the e91 is sick.
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