DIY_EFI Digest V1 #244

[talltom]

>------------------------------
>
>From: rickydik at ix.netcom.com (RD Rick)
>Date: Sat, 24 Aug 1996 00:28:38 -0700
>Subject: Re: Djetronic EFI: was ZEV / REV
>
>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.

I have to disagree. The bosch service manual claims that it is a timed
injection system.

  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 ?

It pretty much does that as is.

>>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?

You were ill advised.

>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.

Not according to the bosch service manual. It sez that their are four
injector circuits with 2 injectors on each, and specifys at what point the 
injectors begin their pulse in reference to valve opening. Maybe you were 
thinking of the system used on Cadillac V-8's, they work that way.    

  There is apparently no real 
>advantage to squirting fuel toward an open valve, as they could have 
>done it and didn't.

Actually they did do it, but several others haven't, and the diferences seem
to be minimal. GM uses a batch fire setup while Ford uses sequential and
there seems no great performance difference. 

>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?

Because some of us would prefer do do something with our lives besides screw
around rebuilding engines. My water cooled 54 Cornbinder eng. runs fine and
has never been rebuilt.