milage indicator

[Franc Buxton]

Jeroen Proveniers wrote:
> 
> Hello,
> 
> I want to have a (accurate) milage indicator in my new car (Ford Sierra 2.0i
> '92). I don't want to use flowmeters (I'd need two, supply and return)
> because these are quite expensive, and I don't want to cut into fuel lines
> anyway.
> So I figured that I could measure the injector pulsewidths. The indicator
> would need the following parameters of the injectors:
> -turn on time
> -flowrate
> -flowrate versus battery voltage
> 
> So the circuit must measure the battery voltage and time the injector
> pulsewidth.
> The car is a four cylinder with two banks of two injectors (there is no
> seperate starting injector). For most accurate metering I would need to
> measure both banks.
> 
> Would this work?
> 

	Hi, Jeroen,

	I wonder if you are taking the accuracy a little too far! How accurate
is your speed signal? Have you measured (to within a millimetre or so :>) ) the
rolling radius of the tyres, taken into account tyre temperature and change of
rubber characteristics with this temperature, for example? I suspect that those
and other factors would have a more or similarly significant bearing upon
accuracy to things like battery voltage and discrepancy between injectors, so
simply measuring pulsewidth on one injector and multiplying by an experimental
'fudge factor' would probably give you enough accuracy. This is the way I
achieved
it on my system, calculating actual fuel consumption experimentally over a
couple
of hundred miles and introducing a suitable multiplier into the measured
parameters.
I estimate this to be accurate to within a few percent, which is the best that
could be achieved, in my opinion, given the other considerations mentioned.

	As always, however, I'm happy to be proven wrong...

	Good luck with the project!

	Regards,
		Franc. 
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