Fuel Computer MkV 2.0TDI innacurate ?

[BeigeJet]

We all know that the speedo is optimistic by ~10%. So if the speedo is optimistic then won't the odo also be optimistic? Which means that you're actually covering less kms than you think (by 10%?) and so your fuel consumption will look less by ~10%.

Check out my logic, guys, it could be flawed.

Hey Cetane,

I checked that out against the numerous speedo checks around where the roads depts in each state have 5km stretches measured out. My Odometer appears to be out by approx 50 metres in 5 km so not an appreciable error. Surely NSW, VIC and SA all can't be wrong!

I know the speedo reads under as most people on freeways seem to zip past. The wife though does most of the driving around town and she ain't light footed.

[Greg Roles]

The speedo, no you cant adjust it but you can adjust the consumption in the mfd.

Im in the process of adjusting mine at the moment. So far ive made one adjustment but it requires more.

Geez, I feel like a dunce, how'd you get so smart with Vag-com? Let us know the tweak mate!

[cetane]

Gps

Hey Cetane,

I checked that out against the numerous speedo checks around where the roads depts in each state have 5km stretches measured out. My Odometer appears to be out by approx 50 metres in 5 km so not an appreciable error. Surely NSW, VIC and SA all can't be wrong!

I know the speedo reads under as most people on freeways seem to zip past. The wife though does most of the driving around town and she ain't light footed.

I'm going by GPS speed readings. Assuming they don't lie, there is a consistent 10% error in the speedo readout.

[gtimk5]

Hi Jackafrica, You failed to mention that your golf has the plug and play tune? Maybe something going on there if it blows a lot of soot out the back mate?
Cheers, Andrew

[gregozedobe]

We all know that the speedo is optimistic by ~10%. So if the speedo is optimistic then won't the odo also be optimistic? Which means that you're actually covering less kms than you think (by 10%?) and so your fuel consumption will look less by ~10%.

Check out my logic, guys, it could be flawed.

My experience (my version of reality ? ) is slightly different in one aspect.

IIRC, for various reasons (as discussed in previous posts) VAG typically design their vehicles to display optimistic road speed (usually 5-10% fast), low fuel consumption (anything up to 20% optimistic), but their odometers are much more accurate (possibly something to do with law suits re warranty in the good ol' USA).

If the odometers were also 10% out then the fuel consmption would be even further out (ie 10% more), as we use the odometer (or trip) reading to calculate fuel used for distance travelled. Unless we have some other way of calculating distance we have to rely on the odometer for the distance. Thankfully I haven't heard of anyone with a particularly inaccurate odometer.

I've read numerous posts that show you a way to display a more accurate speed via a special function in the climatronic controls, so if you have that fitted it might give you a good idea of just how optimistic your speed is. You have to press various buttons in special ways to access it, and I can't recall just what it is (do a search on climatronic in the various VW forums and I'm sure you'll find it).

[jdd]

I also keep a detailed record of every fuel fill-up in a spreadsheet.
The MFD average for the tank is pretty much spot on every time (TDi Pacific).
The worst it’s ever been is 0.1 l/100km out (fractionally optimistic).

I have also checked the Speedo with a GPS and found it consistently reads about 8-9% lower than the GPS. I’ve found the odometer matches the GPS exactly over a 250k trip.

[jackafrica]

Hi Jackafrica, You failed to mention that your golf has the plug and play tune? Maybe something going on there if it blows a lot of soot out the back mate?
Cheers, Andrew

Hi Andrew,
Smokes with or without the plug and play when you put the foot down. Not all the time though, which for me is the confusing part. No doubt it is a diesel trait or something explainable.

Cheers
Richard

[simonn]

Hi Richard + Readers,

I am a new owner of a 1.9TDI VW Jetta 2010 model.
I too am keeping detailed records on what the MFD displays for average fuel consumption of each refill V's manual calculation of litres / km's *100.
There is a considerable difference, I have only recently written to VWA directly. I hope to have this rectified.

I would love to hear from others about their experiences.

Thanks,
Simon.

[gldgti]

Wow, someone dug up this thread! Last post was 2 years ago .

The MFD is really just a toy that helps you keep your foot out of it and drive more efficiently. I dont see why it ought to be 100% accurate, as you have a fuel gauge anyway. I doubt that having the MFD read optimistically is a big conspiracy on the part of VW either - only the foolish would ignore a real world calculation often easily done in your head after you fill up against a dashboard gimmick.

Good luck with your application with VWA to have the problem "rectified".

[simonn]

a variation of 20% is a fault.

[Chook47]

For those with an iphone, have a look at Road Trip Lite. You punch in cost/L, number of liters and the Odo. Gives cost and milage with a little graph to compare different fills. And its free.

[yowie]

[QUOTE=gldgti;
Wow, someone dug up this thread! Last post was 2 years ago .

The MFD is really just a toy that helps you keep your foot out of it and drive more efficiently. I dont see why it ought to be 100% accurate, as you have a fuel gauge anyway. I doubt that having the MFD read optimistically is a big conspiracy on the part of VW either - only the foolish would ignore a real world calculation often easily done in your head after you fill up against a dashboard gimmick.

Good luck with your application with VWA to have the problem "rectified".

I think people would like to see their investments treated by VWA a little more seriously than that
We keep a pocket calculator in the door and do our own fuel efficiency calcs. Around town 6.6 so far, and country as low as 5.1 from memory.
i dont keep records, but maybe we should.

[Transporter]

Well unless you precisely measure the fuel that you put in the tank, you can't prove that MFD is inacurate? I know for sure that the pumps are not accurate!

[yowie]

So what is the allowable variation by Trade Practices or Consumer Affairs, Fair Trading in Qld or ACA, for that matter?
Surely nothing like the ten or twenty percent variation above?

[gldgti]

Holy cow.

If the door falls off, if the seatbelt doesnt lock, if the brakes fail, if the engine runs away - all these things are valid concerns. If you are deeply troubled about your instantaneous fuel consumption readout being 5l/100km instead of 6, you might think about some of the things those less fortunate than ourselves have to deal with every day - like finding their next meal, clean water or trying not to get killed. For crying out loud...

Thread closed.