Add-on systems which affect output pulse width?

[Chris Conlon]

"Andrew Brownsword" <asword at telus.net> wrote:

>  It seems to me that this could be problematic if the ECU was designed to
>expect a particular voltage range and the stock airflow meter generated that
>full range ... in other words there is no buffer for going beyond the
>expected range of values.  This seems fairly reasonable for an N/A engine
>since it is extremely unlikely that the car will have to deal with >1
>atmosphere.

I'm not going to get into this, really. You may very well run
into problems, especially with ignition timing, when you try to
trick an NA ECU into running much boost. (If you aren't
reprogramming it, that is.)

>  The alternative is to modify the ECU's output, which is a time dependant
>pulse width.  It simply isn't possible to have full remapping control over
>the output because by the time you know what the pulse width is, the time at
>which you have to send it to the injectors has passed.  It occurred to me

You can get very close, though, and very easily, in at least a
couple different ways. This presumes you're running injectors a
good bit larger than stock and will not need to lengthen the
pulse. Take your basic HC11. Wire a switch (power mosfet most
likely) in series with each injector drive circuit, watch for
voltage drops, ground ref, etc. Control each switch via output
compare line. Also wire up input compare lines so they can
detect when the ECU is *trying* to fire the injector,
independent of your switch's position. (If you have more than
4 independent injector drive circuits, see 68332 instead.) Now
you can easily read RPM and load, more or less, via input
compares. You have a map, and for each rpm/pulse width point,
look up a new pulse width. (Or just multiply by old injector
size / new injector size, correct for short PW, etc etc.)
Leave each output compare line (switches) on, until the ecu
fires that circuit. You'll get an interrupt and time count
via input compare. Calculate how long you want the pulse to
be, program output compare to turn off at that time. When IC
turns off again, take another interrupt, turn OC back on.

You can update RPM and desired-PW info at each injector firing
if desired. It is "behind reality" but not by much. Issues
exist with p&h drivers, need a dummy load, etc, or just supply
your own drivers. (Assorted details omitted, none too tricky.)  

I already have to do this (and more besides) for my semi
insane supercharged MR2 project, ugh. Lucky for me the ECU
already understands boost, timing retard, knock sensing,
etc, it just needs a few white lies about airflow & injector
sizes.


Now I had some questions for you, since you seem to know
Ford/Mazda stuff well. I did some searching for answers
but got confused and set it aside. I'd like to get an
MX-3 v6, and do some engine swapping. I've heard that a
2.5l v6 from the MX-6 (or 626?) will basically drop in.
Wasn't there a 2.5l *turbo* Ford Probe GT engine at one
point? If so would it drop in w/o much work? Basically I
think the MX-3 is cute and would get one if I knew I could
grab a decent turbo engine (well, a whole front cut) from
something and drop it in pretty easily. (Ignoring ECU hassles
of course, got to have some fun!) I know there are aftermarket
turbo kits, etc, but I was hoping for a factory turbo motor.
Am I just real wrong or was there such a beast? I'm pretty
sure there was a not-common MX-6 turbo... comments? Thoughts?

   TIA,
   Chris C.