[middy]

The results are in from my little experiment.  I have just completed a tank of fun driving, i.e. powering away from the lights, some trailer towing, A/C use etc. etc.  The tank before that I drove like a granny, i.e 0-60 Km/h in 10 minutes, that sort of thing.

Granny Driving:
     Trip computer:                5.6 L/100Km
     Actual consumption (*):   5.9 L/100Km

Fun Driving:
     Trip computer:           5.9 L/100Km
     Actual consumption:   6.2 L/100Km

(*)  Actual consumption is calculated from the actual number of litres of diesel I managed to squeeze in up to the top of the filler neck.

Conclusions:

There is stuff all difference in consumption between granny driving and fun driving, and I know which method I prefer.   8)
My trip computer reads 0.3 L/100Km too low based on the actual consumption.

[Dazzler]

Nice little experiment Middy. From my experience and others I am surprised the computer is .3 under-reading I would have thought closer to .1 out only.

It's hard to drive like a granny for a whole tank full 

[EymaTeapot]

Hi Middy.
I am with Dazz. I am surprised that your trip computer versus actual is so far out of whack. on the couple of occasions i have checked mine, i have found it to be very accurate.
Your actual consumption though is very much on par with mine though.

[Dazzler]

My average appears to be 5.5 lately.. I drive like a granny for a while and it sits around 5.2 or 5.3 but then I forget... and up she goes to 5.4 or 5.5.

Hills are the killer though if I drive on only flat roads I can get 5.0 or better soon as I start climbing hills my average goes up 

[davet]

Like middy I'm seeing .2 -.3 difference between Trip and actual also.

[Lakes]

I have to go off the full tanks economy, but if a trip PC was working out economy while you are doing all country miles, then you go to the city and do say 100k in the city and fill up work out economy, i'll say the trip pc will be out by more as would still be calculating at country economy till it fully works out the new rate. just normal with any trip pc. when i drive easy in country best i see is 4.4L/100K when i drive fast in the country 4.9L/100k, in sydney drive fast 6.1L/100K drive easy 5.1L/100K tyre pressure driving style fuel you use can all play a part weather plays a small part too. at least from what i have found over 10 months 27,000k not one problem no flat spots she is fine.

[Rubix]

I had a reading of 11.6L/100k the other day (I've been leaving the car running with air con while baby has a bite to eat) and yet I was able to fill up exactly 38.8L for 388km of driving... which to me calculates to 10.0L/100k. And on both fill ups I kept filling up until I could see the fuel coming back up, and then I put a bit more in... and a bit more in... until I knew there was nothing more going in.
Thats a deviation of 1.6L/100k.

[Lakes]

Rubix, that could be caused by diferent contions all with the one tank and have confused the trip pc. like idleing with air on to keep baby cool, that could be anything up to 1 litre per hour. my falcons trip pc tells me i am useing 1.8 liter per hour just idleing if i turn air on there is very little difference but thats cause of large motor. would make the smaller motors work harder.


Well i just got back from a trip i filled up on thursday night did the 20 k trip to work then left friday from work went west via M4 up to katoomba in heavy peak traffic went out to mudgee then came home through Orange and Bathurst as had to see friends. just filled up worked out at 5.1 L/100k and i was not takeing it easy so happy with that.

[Rubix]

I figure a smart computer would calculate the amount of distance travelled divided by the estimated drop in the fuel tank since the trip was last reset.
That would be smart.

[LuciferDarklord]

I would like to know exactly how the trip computer works out fuel useage.  There is no flow meter of sort in the fuel line, and quite a bit gets returned to the tank so it would have to have 2 flow meters (one in supply line and one in return)  I'm guessing the ECU calculates it based on injector opening times and fuel rail pressure? Anyone know?

[Lakes]

i was thinking they would have a fuel flow meter, should try e mailing Hyundai see what they say?

[LuciferDarklord]

I think the answer might be here https://www.i30ownersclub.com/forum/index.php/topic,2413.0.html
Have a look at the "fuel quantity" field - 7mm3 which would be 7 cubic millimeters per cycle I would imagine.  The computer could add this up based on RPM, then divide per distance travelled.  Nifty.

Another interesting field is 'throttle flap actuator' - so that vacuum line going to the 'throttle flap' must be modulated by the ecu to control position, so its not just on/off.

Interesting data to see inside the 'brain'

Also the 'frictional torque' etc are very intersting indeed.  Would be good to see if that varies much over the run-in period.

[EpOcH]

I am unsure exactly as to how the i30 measures fuel for the trip meter but based on my other car (and it may well be different) I'ts a combination of fuel pressure and injector pulse widths with rpm playing an obvious part.

Frictional torque (again from my other car) has tables to derive this value in the ECU(along with torque from A/C and accessories).


[deleted]

[LuciferDarklord]

Is this frictional torque a 'read-only' figure thats inputted from the factory ROM, or is it calculated some how? 
As for the fuel usage - yeah I agree, the orifice of the injector is know, duty cycle, RPM - voila - ECU has a total volume of fuel per pot per cycle.  I think the common rail tuning box would confuse this reading....

[EpOcH]

The screenshot is from my stock tune in my v8, Its values are 'read-only' when running and not calculated.

I think the common rail tuning box would confuse this reading....

I don't think it would. Most of these tuning boxes tinker with the inputs to the ECU, basically getting the ECU to add fuel or increase pressure. As it is the ECU that is doing adding, it knows how much fuel is being used and should still remain accurate.

[EpOcH]

I think the common rail tuning box would confuse this reading....

I don't think it would. Most of these tuning boxes tinker with the inputs to the ECU, basically getting the ECU to add fuel or increase pressure. As it is the ECU that is doing adding, it knows how much fuel is being used and should still remain accurate.

But its not reading an accurate signal from the common rail fuel pressure sensor , so it can't accurately know how much fuel is going in, the whole idea of the tuning boxes is to trick the ecu into adding (or removing) fuel by modifying that signal.

This may or may not be relevant.  My stock standard i30 trip computer is always very close to the calculated fuel economy readings.  However, the Scanguage II gets all confused when the a/c cuts in.  It then under reads by a considerable amount (or is that over reads).  Anyway, what happens is the fuel economy reported by the Scanguage is far better than the real world (and the trip computer).  The a/c also increases the boost reported by the Scanguage by approximately 2 psi.  This I believe to be correct.  I believe the boost is increased to compensate for the extra load of the a/c compressor.  I have experienced a slight increase in power when the a/c cuts in (driving at 70-80kph).

Now the Scanguage is getting its info direct from the ECU, I assume.  However I have no idea where the trip computer is getting its info.  What's happening here I do not know.  By the way the Scanguage behaves itself in our Getz 1.6 petrol.

Bob

[LuciferDarklord]

I think the common rail tuning box would confuse this reading....

I don't think it would. Most of these tuning boxes tinker with the inputs to the ECU, basically getting the ECU to add fuel or increase pressure. As it is the ECU that is doing adding, it knows how much fuel is being used and should still remain accurate.

My thinking here is that the ECU calculates fuel flow based on two parameters...  Differential pressure across the injector orifice, and opening time.  Differential pressure would be derived from [injection pressure - cylinder pressure]  Cylinder pressure 'could' be mapped based on airflow, boost pressure, intake temp, crank angle and amount of fuel injected on previous 'shots' in the same combustion cycle (pressure inside the cylinder would rise sharply, trying to hold the fuel back). 

Injection pressure is just the fuel rail pressure.  As the tuning box is presumably fiddling with the sensor readings to the ecu, I'm guessing it would throw the whole calculation out the window.  This is only guessing, but seeing the 7mm3 value on that ECU readout, it seems logical the ECU would be calculating injected fuel quantity. 

If you have a fixed size orifice (which the injector does), fuel flow rate will be proportional to differential pressure across the orifice.  On one side is the common rail, the other is inside the cylinder.