Why does my car think it is getting 30mpg when it is not even getting 20mpg?

[X-ZZ4]

It's always read high, but my display is usually very dim so I never pay attention to it anyway. But sometimes, usually when it is colder, the display works ok for a while.

Regardless, it was always displaying around 28mpg. I've owned it for a year now, and never reset it. Another reason to ignore it...totally false.

But about 2 tanks ago, the display was working good when I got gas, so I decided to reset it. I was curious to see what it would read after a reset.

Now....about 2 tanks later....my display decided to work well again today. It now reads 30.2mpg. I always do simple math and manually calculate mileage when I fill up, and it's usually about 18mpg.

So why is it so far off? Is this common? Is there a fix?

[X-ZZ4]

Ok....I know.....search is your friend.

I searched and only went a couple pages deep before posting because I was only finding crap on MPG of the newer cars. So I posted. Then I kept going deeper in the search and found this....

The range of adjustability in VAG-COM is 85%-115%. Mine was reading about 14.5 mpg when I really get 20mpg. I adjusted the consumption to 85% and now it shows 17mpg. So, I doubt you will be able to lower yours that much. But try to make it 115% and see what happens. Copied from the wiki:

"If you change fuel injectors, your instrument cluster will estimate your fuel consumption incorrectly. Use VAG-COM to adjust it by going to Instrument cluster (17) -> Adaptation (10) -> Channel (03).
Unfortunately, you can only set it to a maximum of 115%. Default is 100%.
If you have access to ME7.x tuning tools, you can completely fix cluster consumption by adjusting the KVB 1x1."

I have 550cc fuel injectors. So I assume this is the cause of this, and there is nothing that can be done. Not a big deal....I don't care much, was more curious than anything.

Does everyone agree? Is this why my reading is so far off?

http://www.audizine.com/forum/showth...lay-proper-MPG

[vlangs]

my car gets about 14mpg

I don't have anything to add to this conversation i just wanted to complain

[glennda5id]

MPG is miles per gallon. The computer calculates miles based off of speedo. Computer calculates gas used based of the time the injectors are open. For a given size injector at a give pressure it will flow a certain amount of fuel depending on how long the injector is open. The computer is calibrated for a certain size injector and fuel pressure. It then captures injector pulse width and frequency to detemine gallons used.

So what happens if the stock injectors flow 300cc/min and are replaced with 600cc/min injectors. The ECU holds the 600cc/min injectors open half the amount of time. If the MPG computer is still calibrated for 300cc/min then the computer is going to think you used half the fuel that you actually uaed an therefore double your MPG.

[stuklr]

Tune is setup incorrectly for the current hardware.