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Ke-Jetronic theory.(explained)
Hey folks.
I figured I'd share the wealth of knowledge I have gained from several
days of indepth examination of the Bosch system. This explination doesnt
cover everything, but does cover quite a bit. Nothing like reading thier
published information, Thatway its not reverse engineering and therefore
not subject to the DCMA.... dont get me started.. Be forewarned I have
high confidence in this information, but There may still be ERRORs. So
feel free to comment.
Anyways.
We all know how the basic system works. Turn the key on fuel pump buzzes
pressurizing the system. you crank the car over with the starter sucking
air in thru the flow meter that opens the fuel distributor that sends
fuel to the injectors that spray continously as a function of air sucked
in.
Well the thermotime switch turns on the 5th injector if the temperature of
the engine block is below a certain temp ( ce-efficient of linear
expansion switch, and if there is fuel flowing thru it. ( I believe, this
is a odd little detail, it just normally effects starting. )
So now your cranking the motor and you've got extra fuel from the 5th
injector spraying, the fuel dizzy is spraying directly into the intake
runners. Now to add a little spark.
The K-Jetronic box (KJ) and the knock box work together to get you spark.
and you have to throw the little ignition module in too.
Lets start with the easy stuff.
Basically the Ignition module is a direct
replacement for the points connection and condensor. It is prolly an IGBT,
but that depends on when your car was made it could be a PNP transistor.
( ** so those of you out there that need to switch a lot of power this
is a good little box to do that.**) It takes an input pulse train from the
KNOCK box on when to fire. Thats all. Power, Ground, Input pulse train,
High current switched output. The coil(transformer) fires when the input
pulse goes to ground. What does this mean to the motorheads that live out
there in go-fast land. this means that you can add retard to your system
by delaying the input to the ignition control module. This is how we are
implementing it in the race car (GRM we need parts -- still, performance
stuff cheap, 2.0L bearings, 16v cams, N2O bottle (to buy),high pressure
hose or flare lines, fittings etc)
Now the Knock box how does it know how to when to fire the coil. Well most
of us know that when the knock box detects the motor pinging it retards
the ignition (delays the time between reaching TDC and sending the output
low to the Ignition module). Did you know that it only does that above
3000 RPM? Me neither. How does it know what RPM its at. Well Im glad you
asked.
The knock box powers the Hall sender unit and gets a nice pulse
train back from it. This is why setting the physical timing is
critical. The system needs to know when the motor is at a known
location. When you adjust the timing on with the distributor this is
what you are changing.
So now the knock box knows how fast the motor is spinning and exactly when
any clyn is at TDC (i think its actually 6degBTDC from the physical
timing). So during starting My guess is that the system fires on the stock
unmodifed ignition map -- simply put given a given RPM fire as some
specific time in relation to TDC. The knock box also gets other inputs
such as the WOT switch, Knock sensor, the other Throttle switch, and an
output from the KJ box. Given a particular input configuration it outputs
a pulse train to the ignition module. It also gets a vacuum input.
Now to the K-Jetronic Box.
What is it? Basically this box was used to interface with the oxygen
sensor. This little beauty ignores the O2 sensor until the the car reaches
a certain temp or the O2 sensor is heated up enough (depending on your
car -- 16v dont have 3 wire O2 sensors, 8v's do). After the car has
reached normal operating temperature the O2 sensor is monitored to find
out if your car is running rich or lean by a voltage output from the
sensor. If it needs to adjust it, it changes the rate of the frequency
valve on your airflow plate buzzes at. It also adjusts the idle with the
idle stabilization valve. Im not sure how, but it has to do with how air
get recirculated. Before the knock box was around the ignition output was
also done thru this box. So the un(knock)corrected pulse train goes to the
knock box.
Brian
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Brian -- tired and grumpy.. needing another Bass(tm)..
88 16v $2003 GRM challenge car http://www.grmotorsports.com
84 0v Next years car got parts?
82 2.0L Topless bunny -- Knock Ignition and bigger clutch. next.
90 90q20v doing daily driver duty.
91 VFR750F everybody needs a 11-12 sec vehicle.
Contact method. Email me for AIM, ICQ, YahooIM, IRC, etc.
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