Mis leading mpg from trip computer

M

marcdavidellis

Member
On a 60 mile commute each way to work across 5 days my trip computer is saying 76mpg which would be great if that was true. I know from calc against fuel put in etc that I have been doing closer to 56mpg. Now I have various issues which an recomended Audi tech (from here) will look at one if them being the temp gauge on the dash is not working at all. Am I right that this would lead to wildly inaccurate mpg from the trip computer?
 
marcdavidellis said:
On a 60 mile commute each way to work across 5 days my trip computer is saying 76mpg which would be great if that was true.
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I suspect that you are looking at the 'live' mpg display rather than the average mpg. Otherwise reset the display using the buttons at the end of the stalk and give it another week to see what you get. As I understand it, Audi's computer records the number of pulses of fuel injected into the engine and the calculated mpg is normally pretty accurate; I would not expect it to be affected by the non functioning of your temperature gauge.

Use the Fuelly app if you need accurate fuel consumption figures: http://www.fuelly.com/
 
It's definitely the average mpg have flicked through to the live which gets up to 200mpg at points if you can believe that. The range is miles out as a result. I've used fuely and calculated with real money spent on fill vs miles covered etc cross checked it always the trip computer is out massively it's at 84mpg over the last 3 trips again calculated and tracked real world is 57mpg.
 
I get around mid 47's mpg on TDI 90.it used to be low 40's when temp gauge wasn't working.So I believe it was telling ECU the engine was cold all the time.I would get temp sensor and thermostat changed as they are cheap to do
 
O07JESTER said:
I get around mid 47's mpg on TDI 90.it used to be low 40's when temp gauge wasn't working.So I believe it was telling ECU the engine was cold all the time.I would get temp sensor and thermostat changed as they are cheap to do
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Marc's complaint is quite specifically about the inaccuracy of the mpg calculation on the DIS display, rather than the reported fuel consumption (which seems a little on the low side). Since he's having the car assessed professionally, that seems the perfect opportunity to raise this; the trip computer may need tweaking while it's hooked up to their computer.
 
Cheers Steve it's not a complaint as such I was just wondering if others experienced the same amount of inaccuracy and if they discovered the origins? That said you are absolutely right a pro should shed some light in this too.
 
My fuel consumption stats on the DIS are pretty consistent and impressively accurate, although I started using Fuelly for a second opinion. Both slightly underestimate my mileage as a consequence of running taller tyres.

The failure of your temperature display on the dash doesn't necessarily mean you have any loss of performance, since the gauge uses a different source of information to the one that controls the injection system. The garage will be able to check the reported temperature with VCDS.

If you find the DIS unhelpful, you might prefer to turn it off for now.
 
Cheers. A little off topic and I have started yo read the thread on tyres and wheels, but I am considering going to 15inch alloys for comfort. But is there a positive impact on mpg of doing this and I am right in thinking skinny width also aids mpg? Current are r17 40 215 which I just think is nuts had the wheel symbol come up a couple of times when on full lock probably to do with width?All the best Marc.
 
marcdavidellis said:
Cheers. A little off topic and I have started yo read the thread on tyres and wheels, but I am considering going to 15inch alloys for comfort. But is there a positive impact on mpg of doing this and I am right in thinking skinny width also aids mpg? Current are r17 40 215 which I just think is nuts had the wheel symbol come up a couple of times when on full lock probably to do with width?
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Skinny width and high pressure aid economy but reduce the comfort.
If you want a good set of wheels at a very fair price, @andrewparkeruk is offering this set is in the marketplace at the moment: https://www.a2oc.net/community/inde...-et38-with-genuine-audi-centre-caps-x4.39073/
Just switch over to Michelin Cross Climates when the Alpins wear out.
If my health were better, I'd have bought them myself.
 
The computer calculates according to fuel injected. It is generally not that wrong unless someone's been messing. 5% error would be ok, more than that signifies a really interesting problem IME.

You are 100% sure there is not a leak at the tandem pump?

I would assume - using spritmonitor.de - that 6l is excessive and around 5 is 'normal' for a mixed non-trivial drive profile. Translated back to those awful non-linear mpg numbers, that's 48 to 56 mpg.
Anything less than that and either you're flat-footed or there is a different problem.
Get the thermostat or the G26 fixed, though, because it will over fuel and that is probably not good for an older VTG turbo which doesn't get exercised very often. You may also see nice black soot out the back which could cause an MOT fail.

- Bret
 
I'm 99percent sure I am achieving 58mpg real world, which is quite good considering 50 miles of my 60 mile commute each way is motorway and rest hill climbs in the country. However the trip computer is saying 82 mpg. Reset it after each run and i achieved 79, 82, 83 , and just now 84mpg. Now one of two things (very simply) 1. The computer is faulty or 2. It's leaking fuel at some point like you said tandem pump etc etc I don't know.
 
And all the rubber hoses turning to mush. Everything standard on the car? @bretti_kivi would a leak not reduce the MPG figure ( actual ) but have little effect on the injector computed value, unless the leak was on the injectors?
 
A leak at the pump means more fuel is pulled from the tank than injected. So fuel used goes up. But the injector volumes stay the same.

If I do the math correctly...76mpg over 300 miles is 3.94 gallons.
If it's actually "only" 60 mpg, then that's closer to 5 gallons. Losing 4l of diesel over a week... that's a hell of a lot.

Right, some more research with the men who know states there's a (metal) pipe between the turbo and the intercooler, it's bolted to the block. The EGR system should also be looked at.

This is going to be expensive with a mechanic looking over it.

- Bret
 
I don't have DIS, but I'm sure I remember reading somewhere on here that using vagcom it is possible to calibrate the DIS
however this seems a long way out
 
Over the next couple of weeks I'm going to keep a very detailed record of miles vs exact diesel intake. What would you expect to get from a 1.4tdi no mods standard on the drive I do (50 miles motorway and 10miles country) driving reasonably sensibly.... I would say 55 to 60 mpg which is roughly what I am getting it's just the trip computer confusing me.
 
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