Djetronic EFI: was ZEV / REV

[RD Rick]

Kalle wrote: 

>Are there any technical sources on the EFI systems used in older
>MB 450 engines, they have analog brain which is a Bosh unit I think
>and a friend of mine has asked if I can modify this to generate timed
>injection for the V8 as at the moment it is a proportional system with
>only 2 phases for all 8 injectors.  Is there any point and do I just
>take the pulse width for the current revolution and delay the start
>until the correct injectors turn has come and then hold the injector
>open when the valve is open for the same time it would have done 
anyway ?
>
>I was told that there were 2 pulses on each set of 4 injectors per rev
>(or was it one per 2 revs) is this right or is it a random 
unsynchronised>dutycycle that just meters/proportions the fuel?

I have the Bosch D Jetronic EFI on my two Porsche 914's, and also have 
a tester for the Djet.  It will test the Merc 450, but I have never 
looked at a Mercedes, as I don't much like radiators and hoses and 
waterpumps.  The D stands for Druck, or pressure.  The later Ljet is 
for Luft, or air(flow).

The Djet uses a Manfold Pressure sensor, which is a transformer with a 
core that is pulled against a spring by vacuum.  It also uses a pair of 
trigger points located in the base of the distributor (dizzy to you in 
SA).  In the 4 cyl VW and Porsche, the trigger points start the 
injection for each pair of cylinders on every other revolution.  It 
would fire four at a time in the V8.  There is apparently no real 
advantage to squirting fuel toward an open valve, as they could have 
done it and didn't.

The Djet is the grandfather of EFI.  It was patentd by Bendix in 1952 
after they reportedly stole it from some guy who developed it in his 
garage.  Bendix licensed it to Bosch in the sixties, at the request of 
VW.  Its first use was in the '68 Fastback/Squareback.

As with all electronics of the era, it is primitive by today's 
standards.  However, it does an outstanding job in a stock engine.  
I am working on mods to it so the hiperf engine in one of my 914 will 
idle below 2000, and still get enough fuel at 6000.

RD
    81 VW Vangon aircooled four with Ljet EFI
    76 Porsche 914 stock commuter with Djet
    73 Porsche 914 hiperf commuter with Djet
    46 Bellanca Cruisair with 165 hp Franklin (Aircooled Motors) engine
    34 Franklin Olympic sedan with 100 hp aircooled upright six

   Except for some boats and ships, all engines are aircooled anyhow.
    Why bother with water?