Bosch ECU Schematic for 1981 BMW 528i

[WERNER_HAUSSMANN at HP-Loveland-om2.om.hp.com]

Hi Michael

I am a little confused.  The L-Jetronic is a multi-port system usually.  
Maybe I have my terms mixed up.  I am not at all familiar with BMW's in 
general, but here what I know about the L-Jetronic


* It is analog (not digital) for the early '80's and a few late '70's.  A 
few late versions were digital, but those are mostly the next generation of 
EFI from Bosch. I know nothing about them. This is realy nice for us analog 
guys that don't want to mess with burning in ROMs.

* The L-Jetronic ECU, depending on options, has the following inputs
  - trottle position input in digital (switch) form, idle, part open, >2/3 
  open
  - Analog (potentiometer) altitude input
  - overboost cut out (by switch)
  - enrichment input (by switch, same as > 2/3 trottle open
  - Lambda sensor
  - Air flap meter (with temperature input) or air mass meter on very few.
  - coolent temperature input.
  - the spark coil is the only input for timing the injectors

* In the system, but not part of the ECU 
  - Cold start injector
  - Fuel Pump relay that only operates when there is a spark coil signal
  - Trottle bypass  controlled electrically and by engine heat for extra 
  trottle when cold running.
  
* The output is control of low impedance injectors.  They are batch fired 
(all fire at the same time) and they fire once for every revolution of the 
crank.

In terms of modification, I think there are only a couple of options.  You 
can upgrade to a later version with more features, ( go the lambda sensor 
if you don't have one) or you can tune it for more power or torque if it is 
running on the Oxygen sensor. But the gains are very small, because it 
already enriches the mixture at wide open trottle. Still you can enrich 
mixture a little.

You can also increase the responsiveness by loosening the air meter spring 
by about two notches. This gives it a little better 'accelerator pump 
action'


If you need a schematic of how the L-Jetronic is hooked up, let me know. I 
have one for a Fuego Turbo. They are all about the same. There are several 
very good books that describe the operation and general hook up.


If anyone has a schematic, I sure would like to see it. Or maybe someone 
has reverse engineered the L-Jetronic and can share some of the knowledge.
Let's hear from all those that have messed around with the L-Jetronic and 
see what they have to say.  I am sure both opinions and facts are welcome.
My experience is with  an 1800cc engine, and MGB.  And it works great but 
doesn't give more noticeable power.

I think the L-Jetronic works well and is easy as an upgrade from 
carburettors, but to increase its performance beyond the designers intend, 
you should go for something like the Tech II with an air mass meter and 
some software to program it.


Werner





______________________________ Reply Separator _________________________________
Subject: Re: Bosch ECU Schematic for 1981 BMW 528i
Author:  Non-HP-glide (glide at shore.net) at HP-ColSprings,mimegw2
Date:    5/17/96 2:29 PM

Werner:

Being a EE I look to EFI electronics where I might be able to improve things 
without major cost impact.

I wonder if it would be possible to turn the L-jet into a multiport 
injection system by firing each injector individually and possibly improve 
the city fuel consumption (its 12+ mpg). Or maybe I could bring out some of 
the parameters and adjust for max performance/ economy. Maybe I could 
repalce with a microprocessor and and do more calculations per second 
resulting in  smoother idle/ economy or performance. I guess I can't leave 
things well enough alone also.



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Michael Glidewell       Boston, Massachusetts   glide at shore.net 
KE1CP     BMW 528i      BMWCCA          http://www.shore.net/~glide/