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Date: Tue Jun 22 15:01:58 1993   
From: "lthompson@fisher.com" <lthompson@turtle.fisher.com>
Subject: More injection ramblings (long)

Has anyone noticed that the 280ZX fuel injection looks exactly like a 
Bosch fuel injection system except for the fact that the parts have 
Japanese writing on them instead of German.  I have an '84 Volkswagon
Vanagon/piece of junk which has an identical injection system as the 
'83 ZX injection.  Did the Japanese get the right to manufacture Bosch 
fuel injections in Japan as a second source and did these second source 
parts end up on the Z's????

[Actually the key technology is licensed from Bendix but in general,
yes the japs cloned the Bosch system.  JGD]

For you folks stepping up from SU's/Webber/whatever carberators to fuel
injection on Z's, I would highly recommend reading the fuel injection
literature written by Bosch.  Unlike some of the Z manuals out there, the
english in the Bosch manuals is excellent.  I will never get over looking
at a cut away view of a '72 Z labeled as "clairvoyant view."  Gives me a 
chuckle every time.

I ended up reading the Bosch manuals after shelling out $800 for repairs to
my Vanagon when it was bad and getting 12MPG.  Ends up, after putting a
ocilloscope on the injectors, that the injection duration was at almost 90%
of the time.  The problem ended up being the oxygen sensor was wired wrong. 
A mechanic broke the wire to O2 sensor while fixing a air conditioner line. 
He realized he better fix it and clamped back together.  Unfortunatly he
clamped it to the coaxial ground braid instead of the center conductor...  
Errrrrrr

[I'm really surprised to hear the oxygen sensor is allowed to have that 
much "bite".  On most systems, the sensor dithers the mixture but
is not permitted to make gross changes.  JGD]

     Things I learned from the Bosch book:
     Please flame me/inform rest if I got it wrong...

        1) Injection duration is inversly proportional to Oxygen sensor
           voltage.  If you ground out the O2 sensor, you will flood the
           engine.
        2) All injectors inject at the same time (Bosch anyway).  After
           seeing all these TV commercials, I thought the injector will
           only inject when the intake valve was open.  Not the case here!
        3) The injectors inject at twice the frequency of the valve 
           open/close cycle (again Bosch does this).

[This is one kind of system.  Called "simultaneous double-fire".  The more
modern scheme is sequential injection that does sync the injection with
the intake valve but it requires a crank sensor and much more electronics.
Sequential injection's benefit for street cars is primarily in the 
area of emissions and is the enabling technology for lean burn engines.  JGD]

        4) The automatic choke equivalent in the Bosch/ZX injection is 
           called an air bypass valve.  It is an electrically heated
           air valve which will bypass some air around the butterfly
           valve when the valve is cold.  They have numerous ways of 
           doing this, but this is how it was done on the ZX and the
           Volkswagon Van.

[Close.  The bypass valve is the equivalent of the choke throttle stop
that causes fast idle when cold.  The extra fuel comes from cold 
enrichment programmed into the ECU and/or a cold start valve, the small
aux injector that sits atop the older Z (and many other) intake manifold.
This is obsolete technology.  Now fast idle is controlled by a stepper
motor controlled bypass valve commonly known as an ICAS (Idle Control And
Starting) valve.  The computer actually controls the engine RPM to a
setpoint.  JGD]

        5) Any air leak down stream from the air meter box seriously 
           screws with the injection computer.  It will fuel starve 
           the engine.
        6) A simple fuel injection only needs a few inputs and one ouput:
             Inputs:
               a) Oxygen sensor voltage (from zero to 1 volt I think)
               b) Some kind of crank position sensor off distributer or
                  flywheel
               c) Air mass charge to pistons (via air meter box).
               d) Engine/coolant temperature.
               e) Air temperature to pistons (via air meter box).
             Outputs:
               a) Injection duration/timing.
        7) More complicated injections add microphones to the engine 
           block which listen for knocking and then adjust injection and
           ignition (ie more inputs and outputs).  Seldom used on 
           Volkswagon vans...
        8) Don't let a mechanic talk you into replacing the injection
           computer and air meter box.  HE IS GUESSING!!!

[Very true.  Alltogether a pretty good summary of the L-jetronic and clone
system.  JGD]


Lee
lthompson@fisher.com


 
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