[Diy_efi] Bosch LH Jetronic v2.2

Torbjörn Forsman torbjorn.forsman
Tue Apr 5 21:58:30 UTC 2005


All LH jetronic fuel injection systems are microprocessor controlled, 
while the L, LE and LU systems are completely analog.

More specifically, the LH 2.2 uses a Intel 8048 series microcontroller. 
In most cases, the control program resides in a 2732 eprom (it is just 4 
kB!), but some LH 2.2 ECUs may have a mask rom microcontroller. Beware, 
mask rom 8048's can execute code from an external rom and there are 
cases where mask rom processors that have become surplus from other 
Bosch projects were used in LH 2.2 ECUs with external rom.

It has no special communication with the ignition system, just that 
ignition pulses are delivered to pin 1 of the LH ECU. They may be 
ignition coil primary voltage, 12 V square wave or TTL level depending 
on the application.

In some cases where the Bosch EZ-K ignition system is used, a digital 
output from the LH ECU (usually pin 24) delivers a load signal (called 
tq) to the ignition system. This is a PWM signal with a duty cycle 
proportional to the engine load.

An interesting feature is that the analog signal from the air flow meter 
is converted to a frequency signal by a VFC (a strange chip made by RCA 
or Harris, it is usually marked Z 91535V2, this is NOT an usual Bosch 
marking). This frequency is used for clocking an 8253 or 8254 counter 
which is gated by the ignition reference signal. For each revolution, 
the microcontroller reads out the counter value. In this way, the 
software does not need to make complex divisions (which would take much 
CPU time for the old 8048) to calculate the injector duty cycle.

If somebody has any information on the Z 91535V2 or has seen it in any 
other equipment than Bosch LH 2.2 and LH 2.4 ECUs, I would be very 
interesting in hearing about it.

/Torbj?rn Forsman


Adam Wade wrote:

>--- WSCowell at aol.com wrote:
>
>  
>
>>It has two ECUs, one for fuel, the other for
>>ignition.  I want to understand much more thoroughly
>>how these two interact and control the engine,  but 
>>cannot find any information anywhere so far.
>>    
>>
>
>There are several very good books on the analog Bosch
>systems.  "How to Tune and Modify Bosch Fuel
>Injection", by Ben Watson, is an excellent resource. 
><http://www.amazon.com/exec/obidos/tg/detail/-/0879385707/qid=1112722933/sr=8-1/ref=sr_8_xs_ap_i1_xgl14/002-4163913-8532820?v=glance&s=books&n=507846>
>
>Also, you will probably want the Bentley book on the
>L-Jet series
><http://www.bentleypublishers.com/product.htm?code=h160>
>
>You might wish to get the big overview of Bosch
>systems book, "Bosch Fuel Injection and Engine
>Management" by Charles O. Probst. 
><http://www.amazon.com/exec/obidos/tg/detail/-/0837603005/ref=pd_null_recs_b_t/002-4163913-8532820?v=glance&s=books>
>
>  
>
>>I am looking for binary files, port/memory address
>>maps, disassembled firmware, anything that will help
>>me understand how this engine runs, and what
>>information it sends to the proprietary Jaguar
>>electronics in the instrument pack and so  on.  
>>    
>>
>
>AFAIK, the L-Jet is an analog system, which means no
>maps or digital data at all.  Analog systems can be
>"tuned" within certain limits by changing component
>values in various parts of the ECU, but since it's all
>analog circuitry, mapping as we know it in the digital
>world does not exist.  The ignition unit is separate
>because L-Jet is fuel-only.
>
>Good luck!
>
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>
>
>		
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