miles/gallon guage?

Steve wrote:
> Don Stauffer in Minneapolis wrote:
>
>> Richard wrote:
>>
>>> Hmmm, I have a friend who has a newer Lincoln, don't remember the model,
>>> that does just that, built into the dash.
>>> I don't know how it is done, per se, but it does show mpg.
>>>
>>> Richard
>>
>>
>>
>> Most of these units had/have a fuel flow sensor,
>
>
> Actually, they DON'T have any such sensor and that's why they are
> accurate. The computer doesn't measure fuel flow, it "knows" to a very
> high degree of precision how much fuel each injector flows per second at
> a given manifold pressure, and it also "knows" how long it's holding the
> injectors open. So its a simple calculation to compute fuel delivered to
> the engine.
>
> Its VERY hard to build a fuel flow meter that is accurate enough to give
> realistic readings.
>

Ah, okay. It was an older one that I was familiar with that had the
sensor. That was on carbureted engines, pre EFI. It used a little vane
impeller sort of gauge. I was quite impressed at how well they worked,
because, yeah, the flow of fuel is pretty low as far as a liquid flow
measurement. Even the 'instanteous' readings averaged over quite a
sample period- maybe that is what made it work well.

Also reminds me of the aftermarket cruise control I installed back in
70s. Had magnets taped to drive shaft near U-joint, taped with
fiberglass reinforced tape. Worked well until the tape would eventually
wear out, and it would throw the magnets :-( Primitive, but it worked.