DIY_EFI Digest V5 #25

[Andy Wyatt]

Regarding William Brennan's idea about building an ECU.

>     I am new to the list, but like everyone I want to build a EFI for my
> car.  I have read through the archives and I just have a few questions. 
> I am also new to the Microcontroller world (Haven't bought anything yet,
> just a lot of reading) and the likes, so please bear with me.  It seems
> that the MicroChips are the easiest to start learning on. Am I correct
> on this?
Yeah, I s'pose so. If you're talking about PICs, you're probably right. You
can get C compilers, Assemblers, Simulators and even BASIC compilers for the
PICs off the net somewhere or other. I'm not sure that a PIC will have the
processing power you require, though. If you're gonna use a lookup table
(fuel map) you'll need a fair bit of ROM. Most of the smaller PICs only have
512 bytes or so. You may be better off using a 68HC11, which has lots of
stuff built in, like several A/D channels, timers and so on, which are all
useful on EFI ECUs.

>  I would like to update the program via my laptop, so which
> chip series might be the best?
You'll need something with EEPROM on it. You can get development boards for
the 68HC11 with 32kB of static RAM, and 32kB of EEPROM, and you just connect
them to your PC to reload the ROM.

> What books or software hardware etc etc would I need.
All the stuff I used for my computer was commonly available. It helps if you
know your micro inside out, so start off with some projects involving the
micro you're going to use, then play with them until you fully understand
the micro. Otherwise you'll just need to learn all about the sensors and
actuators you're going to use on your engine (ie what voltage the sensors
give out under different conditions, how to drive the injectors etc) and of
course you'll have to figure out an algorithm to determine how much fuel to
inject, and spark timing as well (unless  you're going to use the old
ignition system..) Most of this you can find out as you go (as I did),
provided you are cluey and take measurements. With my EFI conversion (from
factory EFI to my own EFI) the way I got a basic idea of fuel maps was to
hook up a datalogger to the factory EFI computer, and drive around, and log
the duty cycle under various conditions.

> I know a lot about cars, just not the electronic stuff just yet, but I am
willing to learn.  Any help would be apreciated.
A basic understanding of electronics is essential if you're going to build
an ECU. A detailed understanding would be very helpful. Even then you'll be
continually learning as you discover new things about the bits you're
playing with. It's a long project - be warned..
> And if it matters, I am going to put the EFI on a 1971 Chevelle w/ a 498"
> Nitrous breathing rat motor for Drag Racing only, and maybe put the EFI
> on my TR7 when I drop the 5.2l rover v8 into it...Thanks!!
A TR7 with an EFI 5.2L V8 should go allright...

Good luck
Andy W :-D