Fuel Consumption Display...

[devondunphy]

Just wondering, I may be nuts but is it just me or does the current fuel consumption display seem a bit odd. It seems to only change in proportion to how far down you push the accelerator pedal and not actually a correct thought out reading calculated by fuel flow or actual engine consumption. Has technology not progressed far enough to give a real readout or something? I've seen them in BMW's as dial readouts and they seem much more correct by leveling out when cruising on the highway under less engine strain, never shooting to absurd numbers like 180mpg, I think they stop around 60. And they always return to a certain number when just idling. In the GTI when you idle it goes to 80, 150, then 200 and then ---mpg all just because your not depressing on the gas pedal at all. Even if your driving at speed and let off the gas pedal it will go to high numbers then ---mpg, then as you tap lightly on the gas it will return to the three digit numbers then erratically back to something semi-normal as you drive on. So to me it just seems to be a fancy gauge to show you in a strange manner about how far down your pressing your pedal and not an actual read out of the fuel consumption. It also keeps that average fuel consumption, I've only been through one tank of gas so far so I won't make any claims on that but i'd like to see if thats the truth either by doing some math at my next fill ups... I call shenanigans, thoughts?

 

[MattyGTi]

well when your idling your not getting any mpg...because youre not moving lol

it goes to --- when u let of the gas as ur driving because that is the injectors cutting off...when u come off the gas and go into deep vacuum the injectors almost shut off...of course they still squirt fuel but just the bare minimum to keep the engine going...

on my old car i had a wideband readout and when i let off the gas it went into deep vacuum and the AEM UEGO would read ---(off the charts lean), and thats one of the most accurate gauges around...

upon throttle tip in (when u describe getting back on the gas), the ecu is tuned to be lean at first, which results in those hyper inflated numbers your seeing..(150mpg)....

we are prolly running 16.5 afr's on throttle tip in....which is pretty lean but okay for short periods of time or at idle....

it evens out on the highway because the car is running stoich (14.7 afr), and if u have a steady foot or are on cruise control...

overall i think its a pretty darn accurate reading...you just cant interpret it the wrong way

 

[jokerific]

No, it's pretty accurate, within ~2 mpg. It's a tad optimistic but otherwise it's fairly good.

 

[Krazy_Z]

The car goes off Injector Duty %. When the injectors are not being loaded "throttle being depressed" there is a 0% duty this is calibrated as idle or not on at all. The super high numbers you see are as the injectors reach 5%, 4%, 3% duty and so on they are literally "dripping fuel" so thus the high MPG. The numbers you see when your driving down the highway with cruise control set are the numbers you need to be judging. If you were to note every MPG read out it would eventually come out to be about normal MPG.

 

[devondunphy]

well heck, thanks for the info.
i didn't realize it was measured in this way. makes sense to me now.
cheers

 

[Keithuk]

Just wondering, I may be nuts but is it just me or does the current fuel consumption display seem a bit odd. It seems to only change in proportion to how far down you push the accelerator pedal and not actually a correct thought out reading calculated by fuel flow or actual engine consumption.

Thats because you have it set on actual which is really a total waste of time. I can get mine to read 25mgp if you put your foot down and 200mpg on the overrun, after 200mpg it just shows ---. Just toggle the up and down switches in the MFSW. Once you see 1 in the top right you are on memory 1, press the OK again and it will switch to memory 2 the overhall average. Press OK again and you back to memory 1 this figure updates every 100m you travel. You can reset either memory if you keep the the OK pressed fo a couple of seconds, normally when you've just filled up.

 

[msm00b]

No, it's pretty accurate, within ~2 mpg. It's a tad optimistic but otherwise it's fairly good.

^ This