E46Fanatics - View Single Post - MPG / fuel gauge inaccuracies - SULEV issues?
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Old 12-06-2012, 03:15 PM   #2
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Join Date: Sep 2012
Location: Old Greg's Cavern
Posts: 12,674
My Ride: '13 128i, '04 330Ci
Originally Posted by crazzy88ss View Post
Ok, so there's some issues going on here that I started noticing a few weeks back.

1.) The fuel gauge is not accurate. It's a 16.# gallon tank, so each of the markers should roughly be at 1/1, 3/4, 1/2, 1/4, 0/0. I've always got about 300 miles out of 11.5 gallons (I always try and get gas at the 1/4 marker due to SULEV fuel system) but lately the tank has been going to about 1/8th to get to 300 miles.

If you see from the picture of the fuel pump, I used 12.75 gallons, which does not correctly match where the needle is on the fuel gauge. The final picture shows the fuel gauge showing a full tank after 12.75 gallons.

2.) Somewhere, something's not adding up. If you take 316 miles divided by 12.75 gallons, you get 24.78mpg and NOT the 26.7mpg that the computer shows.

I've ALWAYS been getting 26-28mpg and 300+ miles out of 12 gallons of fuel but now the numbers are not adding up in anyway.

Any ideas of what's going on?
Have you ever changed your fuel filter? I don't know if this is possible on SULEV cars. Maybe your O2 sensors are going or your MAF sensor is dirty.

3/4 of a tank is 12 gallons so with 12.75 it should be past the 1/4 marker like it is. That might be a little far, but fuel gauges aren't that accurate ever anyway.

Oh and if that 26.7 MPG has been established over a couple thousand miles, then 300 at 24.7 is not going to move the average much. Reset the meter for this next tank and then compare the values.

Last edited by WDE46; 12-06-2012 at 03:19 PM.
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