MPG / fuel gauge inaccuracies - SULEV issues?

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?

Originally Posted by crazzy88ss

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.

Read up on the fuel level sender. I think it may be contributing to your issue.

Originally Posted by WDE46

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.

The fuel filter can't be changed on SULEV (that's why I don't go below 1/4 tank).

The 26.7MPG is over just one tank of 316 miles; I reset it every single tank.

My gauge/MPG has always been deadly accurate (i'm a #s person, and often calculate it manually. That's why I picked up on this issue "quickly").

I found another thread here (http://forum.e46fanatics.com/showthread.php?t=592414) that might be related to my issues. Can anybody else confirm/deny they're related?

You should just sell your SULEV before the warranty expires and get a normal M54. Sounds like something may be about to break.

Originally Posted by WDE46

You should just sell your SULEV before the warranty expires and get a normal M54. Sounds like something may be about to break.

That's the plan. I still got a few years on it, though.

DISA, VANOS seals, O2 sensors??

Suggest you also check to see if you can use the 3rd link below in my signature to determine if your tank levels and sucking jet pump are working correctly.

I do think the fuel filter may be part of the tank on the SULEV, hopefully it is not as fine a filter as the regular cars??

Suggest you also perform a pressure & volume test on the fuel pump assuming the SULEV actually has a test point on the fuel rail?

Originally Posted by jfoj

Suggest you also check to see if you can use the 3rd link below in my signature to determine if your tank levels and sucking jet pump are working correctly.

I don't have access to a windows-based laptop at work or home or school.

VANOS is an interesting thought... the power is fairly weak at low RPM, but would VANOS impact fuel consumption/reporting?

Originally Posted by crazzy88ss

I don't have access to a windows-based laptop at work or home or school.

VANOS is an interesting thought... the power is fairly weak at low RPM, but would VANOS impact fuel consumption/reporting?

You could check your DISA. That helps provide low end torque. It won't affect fuel economy much though.

YOU DON'T HAVE ANY ISSUES.

The fuel gauge is nothing more than an indicator of the difference in F and E. The tank is larger at the top than the bottom, so you can go 200 miles on the first 1/4 tank of gas, and 100 miles on the last 3/4 tank. This is normal.

When the gauge says 1/4, it is safe to say that you need more gas soon. When it says 1/8, then the urgency is increased. But just because you can drive for three days on the first 1/8th tank and only three hours on the last 1/8th does not mean there is something to be fixed.

Originally Posted by crazzy88ss

I don't have access to a windows-based laptop at work or home or school.

VANOS is an interesting thought... the power is fairly weak at low RPM, but would VANOS impact fuel consumption/reporting?

Link for Hidden OBC Menu - http://forum.e46fanatics.com/showthread.php?t=239619

VANOS and DISA can impact lower RPM performance and likely can reduce fuel economy due to lower torque availability.

Originally Posted by jfoj

Link for Hidden OBC Menu - http://forum.e46fanatics.com/showthread.php?t=239619

VANOS and DISA can impact lower RPM performance and likely can reduce fuel economy due to lower torque availability.

Oh those are built into the car's computer; ok thanks.

I'm not familiar w/ DISA; where can I read up on that?

See first link below in my signature.

Originally Posted by crazzy88ss

Oh those are built into the car's computer; ok thanks.

I'm not familiar w/ DISA; where can I read up on that?

You can inspect the DISA very quickly. You only need a T40 torx socket and a 10mm socket. You remove the airbox, MAF sensor, and then the DISA. 4 bolts total and a hose clamp.