DIY_EFI MB 450 Djet

[RD Rick]

Talltom replied > 

>>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. 

No, I just was going on very old memory.  You are right, four pairs.
   

>  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. 

Bosch did it in some 914's, not others.  

>
>>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) 
>>    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.  

Well the cornbinder engine in my '63 Metro needs to be rebuilt.  
Wanna' help?

RD