Hey guys, Just thought id drop a thread on something I have only just picked up about my fuel economy in my car. VY 02 S/C Calais. I have been looking at my AVG Litres Per 100 on my Digital display and have been getting around 15.5 doing basic running around town etc. But I have only just discovered that the "Fuel Used" Digital Display is very different to the Actual Fuel used. Eg: Went to fill up today. The Display read "68.46Lt Used" I actually filled up at "63.76Lt's". I have done this test previously over 3 Tank fills and have noticed between 3-5 Litres Difference. This means that my AVG Litres Per 100 would really be lower. I adjusted the Calibration for the "Fuel Used" on my Cluster a little lower from 100% to around 94% which dropped the Litres per 100 down from 15.1 to 14. Am going to test it out over a few fills and see how it goes. Has anyone seen/had this before and have I done the right thing???
it really depends on how full you are filing the tank, are u sometimes filling the tank higher in the filler neck than others, cause the filler neck will hold a easy 3 litres. also were different servos used, as some read different at the bowsers, so u could be getting these few litres for free. also on your car u can enter dash reading display, only when on start up or turning ignition on, this will tell u fuel level in tank, but just remember if your filling it up in the filler neck, this wont read correctly. the advise id give is let the car run down to just under a full tank on fuel guage, then enter dash mode and see. and then retry this at 1/2 tank. the fuel usage is worked out of engine load, injection time and rpm, and a few other factors, maybe uve found that the scaling of the injectors in the factroy tune, is out slightly. so there are many things that can cause your fuel usage to be different to the dash, but here is a few things it can be. the only true accurate way u can test this is to remove the tank and drain the leftover and measure and then fill tank with confirmed reading from container not a bowser pump. cheers. let us know how u go.
Calibration Process. With fuel used, it is probably best to calibrate over a significant number of tanks. I try to use around 500 litres, and use the same pump for the first and last fill. That allows a pretty accurate calibration. The error analysis on one refill would be potentially pretty high. I would leave it at 94%, and keep records for a few weeks or 500 litres, and then re-calibrate.
