I may have lost it here

[William Shurvinton]

Hi Huw,

I'm in North Hamphire.

The MAP to MAF conversion has been put on the back burner for the time being
as
1. I haven't scored an ECU yet to play with
2. Not enough interest from the Se7ens guys
3. I'm preparing to fit some GM ECMs to my rotary engine as spark
controllers which will take much time
4. Not too much Hacking has been done on those motronic units
5. I still have an unfinished DIY-WB (only 2 components mind)
6. I also have a megasquirt on order

But I am looking at ways around the air flap problems in 205GTi's which
could be solved by analogue methods, although with the prices of used GM
bits it hardly seems worth it. Basically they run really well if you crank
down the spring resistance, but then idle gets awful, so you need a way of
level shifting to compensate. Problem is some Jetronics used linear pots on
the air flap and some use log.

The PIC idea is interesting, but you always add features to support X-Y
mapping and could end up with a universal anything to anything box that is
more complex than the ECU it interfaces to.

For example

SD to MAF ECU
SD to AFM (linear)
SD to AFM (log)
alpha-n to MAF
alpha-n to AFM
etc

And all this for an ECU that is fuel only, less adjustable than a DCOE carb,
with clockwork dizzy, when £25 could get you a working 1227730 that can do
fuel, 3-D spark and a host of other do-dads that I haven't even worked out
yet. A Quad op-amp on the other hand is pennies. However the challenge to do
it 'cos you can' still lingers in the back of my mind

Bill

P.S. Below is a section from a post last week by Eric which explains the
math

.
------------
   f(RPM + MAP + IAT) == f(speed + density) == estimated flow

(IAT == Intake Air Temp, required to turn MAP into density.)

VE is usually assumed to be encoded in the function rather than a
parameter to it.  This is the source of that fundamental difference
between SD and MAF: when I change engine characteristics (big cam,
headers, porting), I change VE, hence need to retune my VE maps to
get SD working well again, while MAF remains more-or-less correct.
----------

----- Original Message -----
From: huw scourfield <huw.scourfield at btinternet.com>
To: <diy_efi at diy-efi.org>
Sent: Saturday, February 16, 2002 9:41 PM
Subject: Re: I may have lost it here


> Hi Bill, the tps signal is linear over degrees of throttle angle, airflow
> through the throttle body is not. I would guess that the map signal is
> linear over manifold depression, whether this is a linear indication of
load
> I really don't know-(I suspect it might be). Anyway, the chances of these
> two curves agreeing are very unlikely to say the least! I would think it
> should be possible with a pair or three of op-amps but personally I'd
invest
> some time in flash progammable pics, 16f874 etc.
> This would take the tps as an input and allow you to use lookup tables to
> convert to a suitable map signal-effectively a mappable system. Ideally it
> would need some interpolation but with just one dimension this is pretty
> easy. I've done some work with these pics and found them to be perfect and
> cheap, even if it takes some time to get "into" them. Where in the UK are
> you bye the way? If you decide to go this route let me know, I need an
> excuse to restart my engine management system. Also this would have
massive
> potential for conversion of thousands of "Kevmobiles" in the UK.
>     Huw
> ----- Original Message -----


----- End of forwarded message from owner-diy_efi at diy-efi.org -----
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