[Q] EFI computers on different engines

[Craig Pugsley]

Hi there,

A freind of mine is on a budget and wants to use a 2nd hand EFI computer
from the wrecker's and adapt it to suit an EFI engine he has (for which
no computer is available).

Essentially the particular computer he has is a nippon denso to suit a
Mazda MA engine (Not really relevant), BUT it has a trapdoor type air
flow meter, air temp, water temp etc inputs and is analogue (early 80s
technology).

He wants me to make up a box that tweaks various inputs to get the
fuelling correct.

My understanding of these trapdoor type systems is
that almost all of the fuelling calculation is based on the trapdoor
potentiometer, along with idle curcuit (switched by AFM or throttle
position), accellerator pump type enrichment (again from throttle
position), cold start enrichment (Water temp sensor) and air temperature
sensor (for air density)

Questions:
i/ If I have a MAP sensor and alter this signal ONLY and feed it into
the trapdoor potentiometer input on the ECU (ie use a MAP instead of a trapdoor
AFM), and leave all of the other sensors STOCK (unmodified), is this
system likely to function successfully?

The concept I had planned to utilise here was to have a series of LM3914
bar graph drivers arranged with some pots to make a 'graphic equaliser'
so the input voltage can make a custom tailored output:

_____          __________________
|MAP|         |    LM 3914 (x3)  |
|   |---------|                  |
|___|         |__________________| 
               |  |  |  |  |  |  |  }=pot that varies output between
               }_ }_ }_ }_ }_ }_ }_   0&5v when that output is on.
                |  |  |  |  |  |  |
                |__|__|__|__|__|__|____________> Output voltage to ECU 

I figure that this should allow a MAP sensor to approximate a trapdoor
AFM, as it is essentially fully adjustable.
Assume for this question that the computer is off a similar type of
engine.

ii/ Before I invest un-nessecary time in this project, am I wasting
effort trying to do this? How hard is it likely to be? Anyone tried
this?

Cheers,
Craig.