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Bad MPG in my XI... is this normal

7K views 34 replies 27 participants last post by  chaso 
#1 ·
I seem to be filling my car up all the time! I drive a 2002 xit manual. I dont have the trip computer but i have calculated that i am getting roughly 19-20mpg. This seems quite low concidering that i spent most of my time on the freeway. I would like to know what other xi drivers are getting. I dont drive with my foot on the floor the whole time so I am wondering if there could be something wrong with my car. I hear that a bad vanos can cause poor gas milege. Any other suggestions if looks like my car is drinking more than it should
 
#2 ·
I'm sure your vanos is fine.

Do you have any codes? I would start there- get them read.

I would replace the fuel and air filters, make sure you have good oil, check your tire pressures, check your intake for any cracks or leaks, spark plugs, and make sure you don't have a sticking caliper, etc.
 
#4 ·
i drive highway and get approx 25-28 mpg.

but also, remember that during the winter, gas quality is poorer..

i would change your spark plugs, fuel filter, air filter, oil and filter as others have mentioned.
 
#8 ·
i find keeping it under 2500 rpms is the sweet spot, easy on the accelerator and limit your braking, utilize coasting into off ramps as oppose to gas pedal and then braking late.. I do cruise control at 68-71 and get good results.
 
#9 ·
I do ~70 miles a day which is about 50% highway at 80mph, 50% rural roads at 50mph.

If I am light on the pedal I can average ~27mpg per tank. If I am enthusiastic I typically score about 22mpg per tank per the OBC.

Make sure your tires are properly inflated.
 
#10 ·
Yeah, i get 24.5 mpg on summer tires and 26.5 on all-season tires.

OP- this is what i would do:

1) check tire pressures first- i like 33Front/36rear
2) Fill up with Shell v-power
3) get a new Mann air filter
4) Check plastic intake prices for leaks

5) Drive half a tank and see if mileage goes up (forget the on-board computer, use the trip mileage counter and divide by gallons)

6) If that doesn't help, replace spark plugs (easy- NGK BRK EQUP) and fuel filter (messy- Mann).

Do you have any other symptoms besides low mpgs? No vibrations, rattles, noises, feelings that seem odd?
 
#12 ·
During the summer I was averaging near 24mpg and now getting just under 23mpg in below freezing temps. I drive about 50-75 miles a day, mostly highway, and I'm usually beating the crap outta the car. Since I have an automatic, I'd assume that what your getting with a manual is well below where it should be.
 
#15 ·
I'm getting 19.9 on my 325xi, which surprised me considering it a 70/30 split of highway/city and I don't have a lead foot. I just replaced my sparkplugs and air filter today...I'll report back if I see an increase. I was surprised that I had OEM Bosch +4 installed and at 82K miles they looked pretty worn.

-Chandra
03 325xi
91 Lotus Esprit SE
 
#16 ·
A little controversy to stir the pot.

All the suggestions for better mileage are good, except the one about changing air filters. Unless an insufficient amount of air is getting through [sic. a completely clogged filter], a dirty air filter will NOT decrease your car's mileage; and changing it out will not increase your mileage.

I know this seems to run against everything we were taught about internal combustion engines; but all these recommendations advising a filter change refer to cars with carburetors, not electronic fuel injection (EFI).

Cars with EFI and Mass Air Flow meters always adjust the air/fuel ratio mix. If the throttle plate is opened, more fuel is allocated. The throttle plate is a much greater restriction to air flow, than any dirty filter could become.

Consequently, at a given speed, the throttle plate may be open wider on a car with a dirty filter; the amount of air is always the same. Hence no advantage to having a clean filter to allow more air... you don't need more air.

The only exception to this dynamic is at WOT wherein the total amount of air available has been diminished. In this case the power of the engine is likewise compromised. But in everyday driving, the air fuel mix always remains the same, regardless of dirty or clean air filter,... and so does the mileage.
 
#18 · (Edited)
All the suggestions for better mileage are good, except the one about changing air filters. Unless an insufficient amount of air is getting through [sic. a completely clogged filter], a dirty air filter will NOT decrease your car's mileage; and changing it out will not increase your mileage.

I know this seems to run against everything we were taught about internal combustion engines; but all these recommendations advising a filter change refer to cars with carburetors, not electronic fuel injection (EFI).

Cars with EFI and Mass Air Flow meters always adjust the air/fuel ratio mix. If the throttle plate is opened, more fuel is allocated. The throttle plate is a much greater restriction to air flow, than any dirty filter could become.

Consequently, at a given speed, the throttle plate may be open wider on a car with a dirty filter; the amount of air is always the same. Hence no advantage to having a clean filter to allow more air... you don't need more air.

The only exception to this dynamic is at WOT wherein the total amount of air available has been diminished. In this case the power of the engine is likewise compromised. But in everyday driving, the air fuel mix always remains the same, regardless of dirty or clean air filter,... and so does the mileage.
Yes, this is true but with a small catch. You are talking about the actual volume of air in the cylinder is the same no matter what, and that is true. The ECU will always determine the amount of air pulled in and inject the appropriate amount of fuel for the equivalent intake charge. BUT, it's not about how much air is pulled in, but how easily it is pulled in. If you choke off the end of a vacuum cleaner, or restrict the intake, the motor works significantly harder to pull in the same volume of air. This brings us to the concept of "ram" air intakes in which the air is literally "rammed" into the intake instead of sucked in by the engine, this brings a small amount of efficiency with it as the engine doesn't have to suck the air in itself. So while the actual amount of air in the intake charge wouldn't change, the amount of efficiency lost from a dirty/clogged filter would have an impact. Now if the question is how much power will you gain, the answer is likely very very little to none. You will, however, gain a few miles per gallon because of the change in efficiency.

Also, I get approximately 24-26mpg driving to/from work in rush hour stop and go traffic. I get 32-35mpg cruising on the freeway for 5 hours straight.
 
#17 ·
pure interstate driving with some hills over a 260 trip I make twice a week using premium branded gas, car running like a champ, only engine mod is Dinan cold air intake and Dinan stage II software and I get 27mpg going 75-80mph and light on the pedal and 225/45-17 tires on stock wheels at 35psi with only me and light luggage in car. I don't spend enough time driving in the city to give any figures.
 
#22 · (Edited)
i get 27mpg if i try to drive good on the highway. BUT, i drive like an a-hole so i get 18mpg highway and usually i get 16mpg city but today i saw the thing in the dash and it said 14.5mpg... prob due to winter gas and excessive idling while cleaning snow off my car.... and single digit weather in the AM when i drive.

car fully tuned up 1 month ago (new filters and sparks)
 
#29 ·
Well I don't drive it like I stole it but I do wring it out every so often. I like to think I drive "normal" as in I keep up with traffic, I'm not the a-hole in the left lane doing 95 in a 60, I don't floor it and slam on the brakes every chance I get, but I don't drive like a grandma either. Traffic is traffic, there are times where you can cruise openly at 65-70 and times when you stop and go for 5 miles. I have zero engine mods on the car, stock air filter, stock spark plugs (which reminds me, they need changing as they have been on there since it rolled off the line), stock everything. Goodyear Eagle RS-A tires (crappy, don't buy them) at around 35psig all around. Driving route is a good combination of hills and flats, I live in the twin cities area in Minnesota if you're familiar with the area. My long distance drives typically consist of a route from MSP to Milwaukee, WI which is a straight shot down I94 at ~75mph the whole way (cruise set).
 
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