Homebrew EFI box

[Alex Samson]

Hi to All,
After more than 4 years I finally found this site that I have been
looking for!  I build EFI boxes for a hobby and every time I start a
project, it is always one big massive guessing game.  I always wondered
if there exists a website or reflector for this activity to help make
the guesses a little less wilder. 

My last project was a complete engine management box for a Subaru 2.2L
flat-4.  This engine went into an early 80's VW Vanagon which had that
famous engine commonly known as a "grenade with a short fuse".  The box
I made was based on an 80C31 for the EFI, another 80C31 for the
distributorless ignition system, and a PIC for the idle stabilizer.  Man
this was a wild project for about 6 months! I did a lot of guessing
because we never had access to a Subaru with the same engine. I had 8k
bytes of scratchpad RAM to log sensor readings to help in developing the
software written in assembler. At present, the van has done over 30K
miles already and I havent made any more changes the last 2 years.  Its
a daily driver owned by a shop mechanic who simply loves the novelty of
his engine setup.   Exhaust has the usual stuff and an O2 sensor which
the box reads for mixture control.  Softwares and look-up tables for the
80C31's are stored in individual SRAMs with  a small backup battery to
allow easy upgrade downloading from a laptop. Naturally, a default setup
is in Eprom.  I used the original Subaru air flow sensor, Cam & Crank
sensors and other peripherals.  Fuel injectors were quite rare in that
they didnt need a step-start scheme, they were merely turned completey
ON or OFF with a straight FET switch (no modulation). The power output
of this new engine is way outside the league of the original aircooled
VW.  The owner once had damaged a pinion gear bearing, then obliterated
a clutch, and the last repair was the transmission getting stuck in 1st
gear.  Unfortunately, the engine has proven to be too strong for the
tranny but otherwise it is very smooth and more appropriate for the van.
One just has to learn to be easy on the throttle to preserve the drive
train.  Would I do it again?  YES!  It was a lot of fun. Kenedy
Engineering in Palmdale made the adapter plate.  

I have started a new project, this time for an old Bosch D-jetronic in a
73 Mercedes 450SLC.  This one is for myself.  At the present, I just
finished installation of an O2 sensor in the exhaust, and I finished a
small box based on the AT89C2051 that processes the EFI points from the
distributor.  The problem with the original system design is that the 4
EFI trigger points are located at the bottom of the distributor and the
lower pair of points get fouled by oil sling.   So my small box
"synthesizes" the action of the lower pair of points by just reading the
upper pair of points.  I will start on the main box next.  The main box
will allow mixture correction with the O2 sensor and will implement a
more positive step-start injector control instead of the weak original
Bosch circuit.  This should hopefully improve emissions, power, and fuel
mileage when I am done.  We use the Atmel AVR at work so I am tempted to
use the AVR for this project this time.  I want to keep the distributor
original with regards to suggestions from others in the past to install
a GM magnetic trigger scheme to the Mercedes distributor.  I want to
maintain full compatibility with the original box so its easy to go back
to stock.

By the way, I was recently at a junque yard because I needed a connector
for a D-Jetronic computer.  I found an old 1972 (or older?) Mercedes 280
SE 3.5 thats been sitting out in the open for probably many years.  The
D-jetronic box was still there although exposed to the rain etc in the
exposed engine compartment.  I picked up the box (and connectors) and
ran it in my bench simulator back home (for which I needed the connector
for in the first place).  I wanted to see what kind of failure this
junque yard box  had acquired after all the exposure.  Would you
believe, this box still works?  I was amazed. This was the first
generation of Bosch EFI and they certainly must have made sure that the
boxes are dependable!

I can go on and on with this subject but I would first like to get
feedback from the members of the list if my topics are appropriate.    

regards to all,
alex samson