simple analog fuel injection

[Chris Morriss]

In message <358E7834.6ABA at worldnet.att.net>, Ron Tyler
<dcmckenna at worldnet.att.net> writes
>> 
>> MAF isn't such a good idea for a simple analogue EFI (not easy to
>> implement anyway).  If you use a MAP sensor, and fire the injectors once
>> per revolution, you will find that a pulse length linearly proportional
>> to MAP will suffice.  You will need to have a gain and an offset pot.
>> The gain sets the slope of the pulse-width versus MAP, and the offset
>> pot shifts the whole curve (or rather, straight line) up and down the y
>> axis.  You can even use the offset pot as a manual 'choke' equivalent.
>> The system won't be as good as a real modern EFI, but I have found that
>> on a small tuned 4 cylinder engine (998cc Hillman Imp) it works better
>> than the old twin 1.25 carbs ever did. (I only suggest you try this on
>> vehicles that aren't subjected to stringent emissions checks.
>> 
>
>  Chris,
>
>         I'm not a hack, but I am familier with the 555. I believe I
>understand the concept, but I dont know how to build in "gain" for the
>MAP. Can you send me a schematic or mabey a brief verbal summary please?
>Also, how would you build in an "accellerator pump" with a TPS?
>
>Mucho Thanx

The accelerator pump is done by adding a differentiated signal from a
throttle pot.  (ie, a signal that is proportional to the rate-of-change
of the throttle position)

I had this in my hand wired prototype.

I understand the critical comments that this simple system might raise,
but don't forget that it's effectively a slightly modernised D-jetronic.
(And it DOES work, honest!)
-- 
Chris Morriss