I would only measure pulse width to get  a relative scale to discern whether the engine is burning more or less fuel, after some basic calculations, of course.  Presumably a type of a calibrated gauge can then show you that relative value at a glance.  This would be enough to teach oneself what the optimum modes of operation are. The trouble is, as I have learned from the MPG gauge in my BMW, conditions vary rapidly as does the gauge display. 

Chris.

Wysłane z iPhone'a

Dnia Mar 26, 2012 o godz. 16:20 Roland <syncronicity1@GMAIL.COM> napisał(a):

> "In principle it should be possible to count the fuel injector pulses.
> (Here's an example of a project to do this kind of thing:
> http://ecomodder.com/wiki/index.php/MPGuino).  One problem with coming up
> with a real-time output of mpg is that the speedometer in a vanagon is
> mechanical.  So you need to grab the fuel injector pulses but also have a
> speed input to the calculation somehow."
> 
> I like this idea, sounds very workable except as you pointed out that the
> default speedo is mechanical.  I wonder if a GPS input would work, perhaps
> there is one of the Android apps that would output the measured speed to a
> couple of pins on the general purpose connector.
> 
> Also, I am not certain, but I think the device would have to measure the
> duration of power applied to the injectors, not just count pulses, since I
> believe the WBX/ECU use time to vary the amount of fuel delivered.
> 
> I wonder how the missing variable might also be available, and that is
> load:  I wonder if that could be simulated by measuring how far the
> accelerator is pushed?  Or probably better a vacuum sensor on the intake
> somewhere.
> 
> Roland
> 
> On Mon, Mar 26, 2012 at 9:14 AM, pickle vanagon <greenvanagon@gmail.com>wrote:
> 
>> I think it's very easy to convince yourself that engine losses are much
>> greater at higher rpms.  Try engine-breaking in low versus high gear.
>> (push down on the gas pedal with the ignition off while you're doing this
>> if you're worried the differences might just be due to throttle
>> restriction).  There's a huge difference at high-rpms versus low-rpms.  In
>> fact, you should even be able to calculate the resistive torque (or force,
>> with respect to a fixed gear) of the engine at different rpms, by observing
>> your deceleration rate and comparing it with the rate you decelerate in
>> neutral from rolling and aerodynamic resistance alone.
>> 
>> But you're right, this is not enough to decide conclusively that the
>> engine is more efficient at lower rpms (and certainly, there are cases
>> where this is not the case).  The system is complicated enough that I think
>> you can't really reason about it extremely precisely from first
>> principles.  But, for practial purposes, I suspect that driving on flat
>> ground at 30mph at 2500 rpm is significantly more efficient than driving on
>> flat ground at 30mph at 3500rpm, since the differences in engine losses are
>> *so* large.
>> 
>> The problem with what your asking for in terms of data is that I don't
>> know an accurate way of measuring fuel consumption in a WBX short of
>> long-term averaging of fuel-ups.  In principle it should be possible to
>> count the fuel injector pulses.  (Here's an example of a project to do this
>> kind of thing: http://ecomodder.com/wiki/index.php/MPGuino).  One problem
>> with coming up with a real-time output of mpg is that the speedometer in a
>> vanagon is mechanical.  So you need to grab the fuel injector pulses but
>> also have a speed input to the calculation somehow.
>> 
>> 
>> 
>> 
>> 
>> On Sun, Mar 25, 2012 at 5:58 PM, Roland <syncronicity1@gmail.com> wrote:
>> 
>>> Thanks all for the discussion.  (this is an '89 2.1 WBX by the way)
>>> 
>>> I don't understand all of the responses, for example I am not sure what
>>> torque has to do with my question.  Sure there are some torque differences
>>> in 3rd vs 4th gear, I can't understand how that might affect fuel
>>> consumption.
>>> 
>>> But what David wrote makes good sense.   In 3rd gear there would be more
>>> losses in the engine itself (piston / conn rod weight reversal, valve
>>> springs, compression events, oil/water pump).  So that suggests that the
>>> MPG would be lower while driving in 3rd gear.
>>> 
>>> But then as a counter argument (if I read it correctly), the engine might
>>> run more efficiently at higher RPMs, at 3400 in 3rd vs 2400 in 4th.
>>> 
>>> I think we need to find some graphs of fuel consumption vs engine speed.
>>> Ideally they would be for the WBX, but perhaps all engines have similar
>>> characteristics.  About 5 different plots, from 1000 RPM to 5000 RPM with
>>> each plot being a different load on the engine.  I think this is what I am
>>> searching for / asking about.  It is almost like reverse engineering the
>>> ECU.
>>> 
>>> Roland
>>> 
>>> 
>>> 
>>> On Sun, Mar 25, 2012 at 3:25 AM, David Beierl <dbeierl@attglobal.net>
>>> wrote:
>>> 
>>>> At 09:56 PM 3/24/2012, Roland wrote:
>>>> 
>>>>> consumed in 3rd gear vs 4th gear?  Now the immediate answer is none!
>>> It
>>>>> takes the same energy to drive at 45 mph in 3rd or 4th.  The wind
>>>>> resistance is the same, the drive-line loss is the same, other friction
>>>>> like tires are the same.
>>>>> 
>>>> 
>>>> But it takes more energy to run the engine faster.  The inertial losses
>>>> from reversing the pistons' direction of travel, the frictional losses
>>> from
>>>> scrubbing the piston rings up and down in their bores, the energy lost
>>> by
>>>> compressing the fuel/air charge and operating the valve train, the
>>>> additional output of the water and oil pumps - these parasitic losses
>>> all
>>>> increase more-or-less linearly with increasing rpm.
>>>> 
>>>> It would be interesting for someone with an OBDII engine to do some
>>>> calculations of no-load operation at various rpm, using the rpm and
>>> engine
>>>> load numbers to determine the relative amount of fuel required to merely
>>>> spin the engine at those rpm.  I wish I'd done it while I still had my
>>>> Honda.
>>>> 
>>>> Yours,
>>>> David
>>>> 
>>> 
>> 
>>