CR170 vRS fuel consumption conundrum

[Richf]

It probably takes readings from a lot more than that!

Mind you for the use it often is it may as well guess

[Fez]

I just have the standard trip computer, it's normally between 2 and 3 mpg out but has been on the nose once. The trip computer must find one or more types of driving challenging but sadly I can't remember the type of driving which caused it to be spot on.

[Kiwibacon]

The fuel computers add up the expected injection volumes to get fuel consumption figures.

The "distance to empty" will be calculated from tank levels.

[Jockdooshbag]

The fuel computers add up the expected injection volumes to get fuel consumption figures.

The "distance to empty" will be calculated from tank levels.

This is what i thought so therefore a fuel leak would show up as lower than normal MPG figures on the trip computer as effectively thje tank is emptying itself quicker for a lower distance covered than normal.

If the MPG on maxidot is about 45mpg then does that not rule out a leak?

[Anddenton]

This is what i thought so therefore a fuel leak would show up as lower than normal MPG figures on the trip computer as effectively thje tank is emptying itself quicker for a lower distance covered than normal.

If the MPG on maxidot is about 45mpg then does that not rule out a leak?

Would a leak not show as higher MPG on computer than what you are actually getting BUT less miles to empty than what the computer is showing.

[Jockdooshbag]

Would a leak not show as higher MPG on computer than what you are actually getting BUT less miles to empty than what the computer is showing.

Maybe i have it wrong way round.

The longer the fuel stays in the tank means the more miles you do = high MPG.

Fuel falls straight out bottom of tank for zero miles = low MPG.

Therefore a fuel leak would = low MPG.

This only applies if actual readings of fuel level in the tank are used in maxidot calculations. It may just read amount of fuel passing the injectors against miles covered therefore a fuel leak wouldnt affect the maxidot MPG figure.

This is pure speculation on my part.

[Kiwibacon]

If you add or remove fuel from/to the tank, it won't affect the ECU's MPG calculation result. But it will change the "distance to empty" value.

[Jockdooshbag]

If you add or remove fuel from/to the tank, it won't affect the ECU's MPG calculation result. But it will change the "distance to empty" value.

So this then means that a fuel leak is a possibility then correct?

[reverse]

To my knowledge MPG is calculated looking at the injectors, not the tank. So how much fuel you have in the tank doesn't matter. MPG is still the same, therefore there is no way of telling if there is a leak looking at MPG figures. Unless the leak happens after the injectors, which is unlikely. Please correct me if I'm wrong.

[Anddenton]

Maybe i have it wrong way round.

The longer the fuel stays in the tank means the more miles you do = high MPG.

Fuel falls straight out bottom of tank for zero miles = low MPG.

Therefore a fuel leak would = low MPG.

This only applies if actual readings of fuel level in the tank are used in maxidot calculations. It may just read amount of fuel passing the injectors against miles covered therefore a fuel leak wouldnt affect the maxidot MPG figure.

This is pure speculation on my part.

My understanding (And this may well be completely wrong) was that the economy readings were obtained by the ECU knowing how much fuel it is injecting into the engine and therefore these would not be effected by a fuel leak (Apart from the car would appear to have not attained the stated MPG).

For the miles to empty either the car knows how much fuel you put in when filling up or it regularly samples the amount of fuel left in the tank. This will result either in the you running out of fuel with the car thinking it has plenty of miles left OR the miles to empty goes down much quicker than expected.

[blueheart]

I thought miles to empty was calculated by what remaining in the tank, divided by the running average fuel consumption readout?

[Kiwibacon]

Since Brimma hasn't done a fill and hand-calc on that tank, I wouldn't even both guessing about potential problems. If he is getting appalling mpg across several tanks and hand calcs deviate further than usual from the ECU's values, only then would I bother looking for problems.

I'm thinking he simply drove a lot quicker than people admit to on public forums and that's why his mpg was terrible.

[taff170]

Most I ever got from my 170 CR FL Octy vRS was a run from Leeds to London and I got 50MPG.

And that was because most of M25 was 50mph limit.

I came back from Hull to Leeds last week and averaged 71MPG at motorway speed in date I say it..... My 1.9 CDTI 150 vauxhall!

I don't think tag at the diesel octy is very frugal tbh.

Edited 20 December, 2012 by taff170

[Davyby]

I only get 160miles per 20L of diesel.

awful economy for mixed driving. And the maxi tells me me fantastic stuff 50+ mpg.

Its a DSG with only 20k miles done.

Im thinkin its a regen issue.anyone had the DPF removed?

you think it may improve consumption?

[rockhopper]

I thought the miles to empty was based on the average consumption for the last 50 miles driven.

The ECU will know how many litres are left in the tank. I seem to remember somewhere in the dim and distant past that you could pull up on the cabin temp LCD the no. of litres in the tank (or was that my BMW?)

The mpg will be worked out by what it is squirting into the injectors and the distance travelled.

Sent from my iPhone using Tapatalk

[silkysteve]

My A3 CR170 has averaged 47MPG over 6,000+ miles since new - that's measured accurately - my last couple of fill-ups have come out at nearly 50MPG. That's compared to 54MPG average that I used to get from my Octy 1.6 CR. A fair compromise, IMO, as the 170 is nicer to drive.

The A3 is getting gradually better economy wise, but I think that's more down to the fact that the novelty has worn off a bit and I'm not driving it so hard. ;-) The bad weather also seems to affect the economy, so I'm expecting it to improve in the summer.

The engine in the A3 is slightly different to the vRS in that it has stop/start and regenerative something or other, although I think they're just gimmicks in order to get the official emission figures down.

[Brimma]

My A3 CR170 has averaged 47MPG over 6,000+ miles since new - that's measured accurately - my last couple of fill-ups have come out at nearly 50MPG. That's compared to 54MPG average that I used to get from my Octy 1.6 CR. A fair compromise, IMO, as the 170 is nicer to drive.

The A3 is getting gradually better economy wise, but I think that's more down to the fact that the novelty has worn off a bit and I'm not driving it so hard. ;-) The bad weather also seems to affect the economy, so I'm expecting it to improve in the summer.

The engine in the A3 is slightly different to the vRS in that it has stop/start and regenerative something or other, although I think they're just gimmicks in order to get the official emission figures down.

So, basically, none of the above has any relevance to my predicament, being a different car, stop/start engine, and centering on your economy figure, but thanks anyway :(

[silkysteve]

So, basically, none of the above has any relevance to my predicament, being a different car, stop/start engine, and centering on your economy figure, but thanks anyway :(

It's similar enough for comparison - same engine. I wouldn't get too exited about stop/start, it rarely gets used in practice.

[Brimma]

It's similar enough for comparison - same engine. I wouldn't get too exited about stop/start, it rarely gets used in practice.

The thread is about the huge discrepancy between the actual mpg and maxidot mpg, not a general CR170 mpg comparison

[littleade]

Filled mine up tonight, now done 850 miles in all and over 445 miles since last top up it's averaged 46mpg, mixed driving, with quite a few short trips under 10 miles-no full welly yet but getting frisky....calculated miles done/litres boughtx 4.5. Don't know what maxidot said as I had a senior moment while flicking between the settings and pressed the button for too long and reset it! Doh

[Brimma]

^^^Thanks for that, I'm so happy for you

[silkysteve]

The thread is about the huge discrepancy between the actual mpg and maxidot mpg, not a general CR170 mpg comparison

I've found that maxi-dot (DIS on Audi) over-reads by about 10%. If my average on the display shows 55MPG, then it'll be around 50MPG true. That's been consistent over my last 3 cars (two of which have been Octys).

Interestingly, it was a similar story with the Toyota Auris Hybrid I hired for a month a while back (It actually returned a poorer average real MPG figure than my current car, although it was considerably better in city traffic).

[silver1011]

So, basically, none of the above has any relevance to my predicament, being a different car, stop/start engine, and centering on your economy figure, but thanks anyway :(

^^^Thanks for that, I'm so happy for you

Christ, with responses like that I'm suprised anyone has the nerve to comment :no:

[Brimma]

Christ, with responses like that I'm suprised anyone has the nerve to comment :no:

To be fair, comments about what consumption figures other people get from a CR170 are, as stated, totally irrelevant

Try reading the OP again to give you a clue

[silver1011]

It's a forum, all I have read is helpful and interesting comments.

If one or more of the posts don't meet your exacting requirements then ignore them.

If you want an answer without the hassle then book it in with Skoda.