Loss in mpg...

[BimmerWill]

Recently noticed that my mpg below below the tachometer seems to drop a lot more than what it used to when under acceleration. Before I was squeezing an easy 26 mpg out of it around town with little to no effort. Now it seems im having to fight for it. Im wondering if it has anything to do with the vanos seals I did. Perhaps didn't get something tightened up enough now its not working properly. Car was dropped on the rear rotor due to a failed jack about a couple weeks ago. I could just be being paranoid but it just seems like their is something holding it back. Rotor doesn't seem to have been warped or anything of that nature. Just curious if anyone has any thoughts.

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[danewilson77]

How old is your intake filter?

[BimmerWill]

Old...I haven't replaced it in close to 60k...

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[alexandre]

Albeit the car had an ECIS CAI when I bought it, the filter was filthy and I'd average 16 mpg in the city. I went back to stock airbox with new filter, cleaned MAF, ICV and DISA and I'm doing ~21-22 now. A filter is $14 so I'd definitely investigate into that. How old are O2 sensors ? I changed mine at the same time, and my MPG is much better now.

[BimmerWill]

Albeit the car an ECIS CAI when I bought it, the filter was filthy and I'd average 16 mpg in the city. I went back to stock airbox with new filter, cleaned MAF, ICV and DISA and I'm doing ~21-22 now. A filter is $14 so I'd definitely investigate into that. How old are O2 sensors ? I changed mine at the same time, and my MPG is much better now.

Yes I will look into an air filter. My 02 sensors are also throwing codes so I guess I should replace those as well..if I were to get a headed later on and trick the computer with dummy sensors would that negatively effect mpg as well?

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[danewilson77]

Damn.....that's a 15k mile item I think. I clean/change mine every time I change my oil.

[alexandre]

Yes I will look into an air filter. My 02 sensors are also throwing codes so I guess I should replace those as well..if I were to get a headed later on and trick the computer with dummy sensors would that negatively effect mpg as well?

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Since you have a prefacelift I think you have the older non-wideband sensors - i.e. they're like $45-50 each on Amazon/BMA/Pelican. Facelift 330 sensors are $100 a piece.

If you get headers you'll only need dummies for the post-cat sensors, and these usually only affect emissions, not your air-fuel ratio. They usually aren't replaced unless they throw codes.

[Ryans323i]

Mine are about $80 from ECS. But first things first, do the air filter. You'll be very surprised! Like Dane, I used to change mine every oil change, 7500miles. Now I have a cone filter (CAI) and I do 5,000 oil changes, and switch my filters (I bought 2) at every oil change or even when it looks dirty. You cant have combustion without air!

[BimmerWill]

Mine are about $80 from ECS. But first things first, do the air filter. You'll be very surprised! Like Dane, I used to change mine every oil change, 7500miles. Now I have a cone filter (CAI) and I do 5,000 oil changes, and switch my filters (I bought 2) at every oil change or even when it looks dirty. You cant have combustion without air!

I tried the oiled cone filter as well as the drop in k&n and they simply just caused my maf to send out false readings. Im hoping to get an oilless high flow at some point but for now ill try to pick up a paper filter. I believe the pr-cats are the ones throwing the codes so im guessing they need to be replaced as well regardless of getting headers or not. I had no idea the filters were supposed to be replaced that often

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[Mr Paul]

Recently noticed that my mpg below below the tachometer seems to drop a lot more than what it used to when under acceleration. Before I was squeezing an easy 26 mpg out of it around town with little to no effort. Now it seems im having to fight for it. Im wondering if it has anything to do with the vanos seals I did. Perhaps didn't get something tightened up enough now its not working properly. Car was dropped on the rear rotor due to a failed jack about a couple weeks ago. I could just be being paranoid but it just seems like their is something holding it back. Rotor doesn't seem to have been warped or anything of that nature. Just curious if anyone has any thoughts.

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With it getting close to winter gas companies switch to their winter blend of gasoline. You tend to lose a couple MPG's with this gas. This could be what you are experiencing.