MFD - Instantaneous Fuel Consumption Issue

[doink]

My MFD, when on instantaneous fuel consumption, works fine while I travel in gear, however I have recently noticed that in traffic when I engage first gear hit the throttle and then pull the stick back out of gear in to neutral and remove foot from throttle to let the car roll along out of gear my MFD fuel consumption fluctuates between 7.0 - 17.0 l/100km when my foot is off the accelerator. It will go back to 1 l/h only after I have come to a complete stop. If I re-engage a gear it also starts working correctly again.

This certainly doesn't seem right to me as I could not be using that much fuel with my foot off the accelerator. This will also throw out my average fuel consumption readings.

Anyone else seen this on manual transmission GTI's or do I have an issue with mine???

[Maverick]

There's no problem, it's not able to be 100% accurate and if you take a note of km's traveled when you fill up and the amount of fuel you can determine the accuracy of the display.

[Guest212]

sounds normal to me. my DSG does that.

I wouldn't call it a very accurate reading either.

[Maverick]

sounds normal to me. my DSG does that.

I wouldn't call it a very accurate reading either.

You can make adjustments to make it more accurate as well using vagcom/vcds.

The instantaneous is never accurate on any car and is not intended to be when engine speed is changing rapidly.

[Guest212]

You can make adjustments to make it more accurate as well using vagcom/vcds.

but who takes notice of it?

Just drive it and enjoy while you can.

[gregozedobe]

.... I have recently noticed that in traffic when I engage first gear hit the throttle and then pull the stick back out of gear in to neutral and remove foot from throttle to let the car roll along out of gear my MFD fuel consumption fluctuates between 7.0 - 17.0 l/100km when my foot is off the accelerator. It will go back to 1 l/h only after I have come to a complete stop. If I re-engage a gear it also starts working correctly again.

I'm going to suggest that it is working as designed, isn't being more inaccurate than usual, and isn't disrupting your average fuel consumption figure either. My logic for saying this is:

The MFD is designed to show a figure for consumption over distance when you are moving (l/100km), OR a figure for consumption over time (l/hr) when you are stationary, and that is exactly what it is doing.

When you put the gearbox into neutral the engine is consuming fuel (it is idling), and the car is moving (albeit very slowly) You are not covering much distance, but the engine is still using fuel to idle, so the l/100km figure is quite high (even though you don't have your foot on the accelerator pedal).

If I'm right, the faster you are moving when you select neutral, the lower the l/100km consumption figure, because you are covering more distance for the same (idling) fuel consumption.

Anyone see any flaws in this explanation ?

As an aside, VW MFDs are often pretty optimistic on fuel consumption, you will get much more accurate figures by doing fill to fill calculations over many fills.

[jausho]

When you put the gearbox into neutral the engine is consuming fuel (it is idling), and the car is moving (albeit very slowly) You are not covering much distance, but the engine is still using fuel to idle, so the l/100km figure is quite high (even though you don't have your foot on the accelerator pedal).

If I'm right, the faster you are moving when you select neutral, the lower the l/100km consumption figure, because you are covering more distance for the same (idling) fuel consumption.

Anyone see any flaws in this explanation ?

Spot on...

Simple calculation to verify: 0.8L/hr when my R32's idling. Coasting in neutral @ 20km/h: 100(km)/20(km/h)=5 ... 5x0.8=4L/100km ... As the car slows down, say to 5km/h: 100(km)/5(km/h)=20 ... 20x0.8=16L/100km ...

Therefore, with the car coasting (and consuming fuel at a constant rate) its fuel consumption over distance, which is what the MFD shows when the vehicle's moving and selected to 'Instantaneous consumption', increases as speed decreases.

[gerhard]

WTF?

Just switch it to trip average fuel consumption and relax If the high reading from cold start bugs you, switch to lifetime average.....

[Guest212]

WTF?

Just switch it to trip average fuel consumption and relax If the high reading from cold start bugs you, switch to lifetime average.....

Or turn the display off.

[brad]

WTF?

Just switch it to trip average fuel consumption and relax If the high reading from cold start bugs you, switch to lifetime average.....

99hour average.

I'm trying to work out why he was doing a tap dance on the pedal/gearlever etc like that????

[bazzle]

but who takes notice of it?

Just drive it and enjoy while you can. Being a Mk5 it will all eventually fall apart, so may as well enjoy it while its going.

Yom

Cant you say 'Anything " constructive

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Instantaneous will show spurious but when you lift off throttle and coast it should go to near zero, when you acc hard it will go high, on cruise it will be half stable with a bit of moving around.

Use the 'avg' setting over a period of time for accuracy. When you fill compare the results. If its out over a few fills then as stated earlier there is small adj in VCDS.

Bazzle


Bazzle