MPG meter. Could it be done another way?

[NEIL_N]

Hi all. I'm a new member and find these threads very interesting reading.

I had posted this another thread but thought it needed to be re-posted as a new thread.

I have a Mazda MX-6 (equiv to Ford Probe) 2.5 V6, And would like to know how much fuel I'm using. I do have an old Zemco ZT10 Fuel computer but it only works on carburettor engines with low pressure fuel delivery.

So. Could fuel consumption be measured using the following idea:

Generate two DC voltages. One proportional to injector pulse width, The other proportional to road speed. The DC voltage for pulse width being done by a gated integrator circuit, And the DC voltage being done by using an LM2907 Frequency to voltage convertor IC. The two voltages can then be applied to some form of comparator circuit that sums/subtracts/multiplies/divides or whatever in order to provide a DC voltage that correlates to the fuel being used for the speed (distance travelled).

Would a third reference voltage be needed (equating to the fuel flow rate)?Again all three voltage would need to be compared and an output a DC voltage required to indicate fuel used.

The DC voltage generated could be applied to a moving coil meter, Or an LED bargraph display (LM3914). Obviously the circuit would have to be calibrated. But once the all the DC input voltages have known relative values, calibration of the display device shouldn't be to difficult.

Any further comments or suggestions or ideas on the comparator circuit please

Cheers

Neil