From: Toosmoky on 11 Feb 2007 17:40
> You thought it was that sized tank, or, you over filled the tank, or both?
> Big differences.
Where are these bowsers? I've never ever been able to put more litres in
than what the tank holds. Never even been able to equal the tank capacity...
Work to ride, Ride to Work...
From: Theo Bekkers on 11 Feb 2007 18:28
> Some of the things it does are measured, others aren't. The result
> when combined is effectivly an _estimate_.
But, but , but Nev's car says 16.23 l/100 kms (or something). This suggests
an accuracy of 0.01%. Actual accuracy is probably 10% but all those
significant digits look so neat.
The Compuguestimator on the Norge says I use 5.6 l.100 kms. Reality at the
pump suggests 5.1.
From: jlittler on 11 Feb 2007 18:30
On Feb 11, 9:59 pm, Hammo <hbaj2...(a)aapt.net.au> wrote:
> <j...(a)nowhere.com> wrote:
> > Hammo wrote:
> >> QR_yh.5250$sd2.4...(a)news-server.bigpond.net.au, "Knobdoodle"
> >> <knobdoo...(a)hotmail.com> wrote:
> >>> "Hammo" <hbaj2...(a)aapt.net.au> wrote in message
> >>>> "jlitt...(a)my-deja.com" <jlitt...(a)my-deja.com> wrote:
> >>>>>>> No; it actuates the injector the exact amount that it's been told to
> >>>>>>> for the
> >>>>>>> conditions it's measured.
> >>>>>>> But it doesn't have any idea what a litre actually is and it certainly
> >>>>>>> doean't have any ability to actually measure one!
> >>>>>> Eh?
> >>>>>> It's measured, but it can't measure?
> >>>>> No, it's calculated based on what actually is "measured" (or more
> >>>>> accurately specified by the efi).
> >>>>> The efi opens the injector for a period according to what it's lookup
> >>>>> table tells it is the right amount given the parameters it has sensors
> >>>>> measuring. It ASSUMES the fuel pressure (and hence fuel flow) is
> >>>>> correct (unless there has been some new fangled advances in EFI I'm
> >>>>> not aware of). I know of no cars that measure actual fuel flow, they
> >>>>> usually calculate your fuel consumption based on the amount of time
> >>>>> they've opened the injectors, and the number of KM's travelled. Those
> >>>>> two parameters are based on a number of implicit assumptions:
> >>>>> - the fuel pressure is correct
> >>>>> - there are no blockages restricting fuel flow
> >>>>> - the size of your tyres are as specified and hence the number of K's
> >>>>> calculated is correct
> >>>>> etc etc
> >>>>> it's a reasonably accurate estimate and more than good enough for the
> >>>>> purposes for which it is used. That doesn't mean the actual fuel flow
> >>>>> is measured.
> >>>> Eh?
> >>>> It's measured but it doesn't measure?
> >>> Why do you keep pretending we've said "it's measured" Hammo; when we've
> >>> quite clearly said the exact opposite!
> >> How does the efi know how much to squirt?
> > Because a human told it what to do, if these parameters are measured
> > (which don't include measuring fuel flow), then do x.
> A human told it to? That is your explanation of the sophistication of EFI?
Yup. Pretty much sums it up.
What amuses me, is that you seem to deliberately be confusing
measuring with calculating an estimate. If someone else tried that
obfuscation you'd be up in arms !
The *measured* parameters for the EFI are things like the exhaust gas
mix (via o2 sensor), duration of injector opening, quantity of air
flowing through the throttle bodies(MAF) or the postion of the
butterfly in the throttle (TPS), engine temp etc.
The measure inputs are then used to calculate other things based on
There are lots of assumptions made during the programming of an EFI
computer, there's also differences in the granularity of the
measurments and hence how well it can interpolate (finite steps in
measurement need to be translated into smooth changes in quantity of
fuel, ignition timing etc).
When you make assumptions about a variable (rather than measuring it),
it is inherently more likely to be inaccurate than measuring it. Yes,
there's also error in measurement, and yes potentially the
relationship *could* be the other way around, but it's not very
Fuel flow in Nev's car is a calculated estimate, not measured (to the
best of my knowledge), the calculation is accurate enough for domestic
use, but it includes assumptions about the values of some parameters,
it is therefore not, by definition, a *measurement* of the fuel flow,
but a reasonably good estimate.
Please note, I've already said all this once. Please try reading it
> >> It must have some idea, after all
> >> it calcs things to L/100 km. it'd have to be more than just chance.
> > Uhuh, it sticks it's metaphorical finger in the air and makes it's best
> > guess, based on the things it does know. It's usually a pretty fair
> > estimate to, same as when I walk outside, wave my arms around a bit and
> > say "I think it's about 22, 24 degrees celsius this morning"
> Yes, you and your "weather station". We have had that discussion before.
yes and you still seem to think that domestic use requires scientific
levels of accuracy, the world ain't a lab, get over it.
Nev's car does stick it's metaphorical finger in the air - it doesn't
KNOW how much fuel has flowed through it (ie no flow measured). It
DOES know that it held the injectors open for N milliseconds X times
over the last 5 minutes, and *IF* it's assumption that it's fuel rail
pressure is Y PSI is correct then it has flowed Z ml of petrol. Of
course that also assumes the temp of the fuel and all sorts of other
trivial assumptions that would make minor differences to the
calculated result. Doesn't matter though because for the purposes it's
being used the estimate's going to be close enough.
And just for the record, same goes for the "weather station" temp
measurement in a domestic situation is mostly for the purposes of
considering your physical well being, so the thermometer saying 21 vs
22c doesn't really matter much, I know it means jeans and a tshirt.
> What does EFI do
> that makes it so special?
Nothing, it's not at all special, it's just a way of adding fuel to an
internal combustion engine, that's nothing special. It does it a bit
more accurately nowadays than the old analogue based carbies, but
there was a fair while there when it didn't. It's no more special;
than any other computer controlled system - why do you think it's
> Why are EFI motors getting cleaner and having
> lower emissions (despite their inherent inefficiencies)?
Better EFI programming, smaller steps between measurement intervals,
more powerful CPUs able to interpolate faster and more often per
second, ability to manage a greater amount of data over a longer
period to calculate more effectively given a wider range of paramerts.
The ability to monitor the gas mix in the exhaust in a fairly
primitive way to be able to then say "oh no lean off the mixture, it's
too rich" (feedback loop on the result)
Also, outside of the efi piece - better engine design - cylinder head
design has come a long way in the last 15 years.
From: Theo Bekkers on 11 Feb 2007 18:32
> Did you miss Nev's point (or Theo's, or someone's) that the readout
> was 4 significant figures, which had had the potential to either show
> that 1) there is no effect, or 2) it is so small more significant
> numbers were required?
It was my point. Did you miss the point I made that the four digits looks
very cute but the accuracy was more likely less than 2 significant digits?
I'm sure Holden can display more digits for you without impacting on the
From: jlittler on 11 Feb 2007 18:33
On Feb 11, 4:13 pm, Hammo <hbaj2...(a)aapt.net.au> wrote:
> On 10/2/07 11:52 PM, in article 45cdc0d...(a)dnews.tpgi.com.au, "JL"
> <j...(a)nowhere.com> wrote:
> > Hammo wrote:
> >> "No; it actuates the injector the exact amount that it's been told to for
> >> the conditions it's measured. It then displays the exact mpg (L/Hr, Km per
> >> kilojoule or whatever) that's it's been told to display too."
> >> That is from up the page! That ain't invented, and it sure aint pretend.
> > Yup, so you've just quoted the bit that shows he didn't say the mpg
> > (etc) were measured. What's your point (1)
> > JL
> > (1) he says knowing full well Hammo doesn't actually have one
> Jeez that was a low blow. I do and I have maintained it. The "volume"
> injected is not a random number.
No one said it was.
> It will be based on parameters that are
> peculiar to the engine and appropriate for the required performance etc.
indeed very good, you were paying attention after all
> Based on that, there *must be* with in a known error range of fuel consumed.
<puzzled look> yes Hammo, I've said that twice now, but thats not a
measurement, thats a calculation based on the things that are measured
and the assumptions made.
> Are we still on the same page here?
Only in the sense that you're repeating back to me what I already said
like you're telling me something