dskblade

What could cause bad MPG readings ? Based on the display in my car , I'm averaging 9.5 / 10 mpg , which is totally ridiculous. Based on my calculations , I'm doing around 18-19 mpg ( makes much more sense right ? ).

Anyways , what could cause this ? It's kind of annoying because I would actually like to see my real consumption and how much I am averaging...

Hope it's not a big fix !

Thanks for your help

GTA_Driver

Worst case scenario - bad fuel sender unit, sits in your tank if I'm not mistaken.

eejimm

The average MPG readout is notorious for being off, usually on the high side unlike what you're seeing. The instantaneous one seems to be somewhat more accurate, as it is driven by measuring the PWM injector signals and the vehicle speed, but it's all dependant on several things that can throw the calculations off, like fuel pressure or dirty injectors.
Best advice is to do the math yourself when you fill up the car, and leave it at that...
Jim

GTA_Driver

Ok juat to clarify. If it's the instantaneous one acting up, i undestand the part responsible for that is in the fuel tank.

If it's the average one, then i don't know.

nm3210

Interesting, you make a good point that something that much off might be a sign that something is going wrong somewhere else. It is possible to adjust the averaging weight in Vag-Com to more accurately match your realistic calculations (see http://www.audizine.com/forum/showth...r-MPG-readings) but again it usually isn't THAT much off. I am assuming that you have tried to clear the memory of the average (hold down the reset button on the washer-stalk) to see if it was just a bunch of funky bad numbers in the memory?

And i'm not sure whether the average takes into account idling or not...anyone know?

dskblade

Both instant and average are affected by this problem.. I've tried to reset multiple times with no luck ; it keeps showing big numbers...

eejimm

Sounds like the cluster is getting bad data, but that would mess up other things I would think...

Maybe look at the measurement blocks in the cluster (group 17) with a VAG-COM to see if anything looks crazy?
Jim