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      02-28-2015, 01:10 PM   #1
bmwusersince2013
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Mileage Dropped Suddenly

Hello there,

I bought used 2011 328Xi from dealer in nebraska on september 2013. The miles on the car were 26500. Recently the car was shaking at idle, stop signals, i took it to the dealer in Iowa since in moved here. I was told that the 2 Ignition coil and 2 spark plugs gone bad and it was said to replace all the 6 spark plugs and ignition coils brand new. The charges were 1200$ close. I agreed to put new. Now during this winter time, I'm starting the car for 10-15 min before i drive in the morning to get the engine heat up. I drive to office 2.5 miles one way. Now i noticed that the Car mileage is totally dropped to 12 per gallon in city, while before it used to give 18-20 miles per gallon in city and on highways 23/gallon.

Could you please help me in understanding what made the mileage to go such low.

I appreciate your help. Thanks
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      03-03-2015, 09:18 PM   #2
E90_boostjunky
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Where in Iowa are you? also if you read the manual I think it says you just need to get in the car and go, don't let it warm up not even 1 minute. and unless you're running your a/c or your driving habit changed then idk why ur mpg changed, what kind of gas are you putting in??
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      03-03-2015, 10:03 PM   #3
bmwusersince2013
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Thanks for your reply... I warm it up in the morning bcz of the weather conditions. The temperature here is severely low. In the morning if i drive without warmingup, there will be more torque generation..It does not pick up the speed, by the time it pickups the speed i will reach my destination, just 2.3 miles away from my location. I use 91,,..i always used Shell or BP. In IA i did not find Shell. I am using BP sometimes COSTCO or SAMS.

Appreciate u r Input.

Thanks
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      03-04-2015, 12:07 AM   #4
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You said it's been cold, did you check your tire pressures? 2 minute warm up is all you need, just keep rpm < 3000 or so until oil temp needle comes off the peg.
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      03-04-2015, 07:05 PM   #5
bmwusersince2013
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I use 91. Yes the tire pressure is correct.
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      03-14-2015, 10:46 PM   #6
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Had a coolant temp sensor go bad once in an E36 and it caused car to run super-rich. Not sure if that is still feasible, but may be worth checking out.
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      03-14-2015, 11:01 PM   #7
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Quote:
Originally Posted by bmwusersince2013 View Post
Hello there,

I bought used 2011 328Xi from dealer in nebraska on september 2013. The miles on the car were 26500. Recently the car was shaking at idle, stop signals, i took it to the dealer in Iowa since in moved here. I was told that the 2 Ignition coil and 2 spark plugs gone bad and it was said to replace all the 6 spark plugs and ignition coils brand new. The charges were 1200$ close. I agreed to put new. Now during this winter time, I'm starting the car for 10-15 min before i drive in the morning to get the engine heat up. I drive to office 2.5 miles one way. Now i noticed that the Car mileage is totally dropped to 12 per gallon in city, while before it used to give 18-20 miles per gallon in city and on highways 23/gallon.

Could you please help me in understanding what made the mileage to go such low.

I appreciate your help. Thanks
It can be numerous factors but I drop a lot of MPG starting my car in the winter as well but not as much as yours. 1200 is pure rape on the price. Any Independent shop will do it for under 500 with parts and labor.

Please don't go by your MPG reading do actual miles how much your car is getting. I remember I reset mine and it said I was getting 11mpg but in reality I was getting 23. I started my car up and let it idle and that makes the MPG drop via computer not in real time MPG.

I get around 18 in winter and 24 in summer. Thats all city driving local. I have no cats full exhaust and mines a manual and I baby it for the most part.
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      03-15-2015, 01:31 PM   #8
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Is your range on the tank significantly lower or just the displayed mileage on your average economy gauge?
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      03-19-2015, 10:03 AM   #9
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Just throwing it out there as well, winter blends of gas cause lower MPG, and it is cheaper. They are switching to spring blends here soon which will cause prices to rise again, but should give you a little better gas milage.
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      03-19-2015, 12:21 PM   #10
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Indeed your car could be running rich: a possibility for all normally aspirated cars at altitude (assuming you're now in Colorado?). That could be causing idle roughness, are your exhaust tips sooty? Difference from that seems unlikely to change MPG that much. Could be other problems. Haha, yea, are you using the computer or doing your own calculations? You may want to get a code reader too, see what the car is telling you....
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      04-05-2015, 10:50 PM   #11
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My 2007 328xi's computer usually tells me 25 - 26mpg (mixed, with ski-rack). When I calculate it's about 3mpg lower. Removing ski-rack is worth another 1-2mpg.

If you're seeing half that, I would still suspect a sensor that is going bad and telling the ECU that things are running hot. That would result in rich condition.

Good luck!
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