Here it is and all the info you would ever need on the bosch k series.
“ This tech told me that the only way the fuse would quit blowing was by unhooking the coil pack. I was stunned at first, since the power to the coil is through a red/light green (R/LG) wire and from a different fuse than the solid red. ”
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The K-Series fuel injection systems are
continuous mechanical fuel injection systems used on a wide variety of
European vehicles, including such makes as Volkswagon, Audi, BMW,
Mercedes, Porsche, Volvo and Saab. The system is one of the most common
fuel injection systems on the market today, but also is one of the
least understood.
The K-Jetronic System
constantly injects fuel into the engine as long as the car is running
and air flow is present to move the sensor plate in the airflow sensor.
The sensor plate is connected to an arm that pushes up on a plunger
located in the fuel distributor. As airflow changes, the movement of
the sensor plate and the plunger increase and decrease the volume of
fuel injected into the engine. Since fuel is being injected constantly,
fuel pressure will have a direct affect on driveability. As a matter of
fact, fuel pressure is the single most critical element when diagnosing
driveability problems in the K-Series fuel injection systems. An
accurate fuel pressure gauge
must be used when testing these systems, with a range of 0 to more than
100 psi. You will also need a digital volt ohm meter (DVOM) that can
read milliamps.
You will work with three
types of pressures when diagnosing these systems: system pressure,
control pressure (also known as counter pressure) and rest pressure.
System pressure is the
total fuel pressure produced by the fuel pump on a constant basis. The
fuel pump must be able to maintain this pressure during all driving
conditions from idle to wide open throttle. As a rule, system pressure
will run about 5 to 5.5 bar pressure, or 75 to 85 psi (1 bar = about 15
psi) and the pump should be able to produce a minimum volume of 1 pint
in 15 seconds. When deadheaded, the K-Series fuel pump will produce
about 1.5 times the system pressure or about 110 to 120 psi. System
pressure is a function of volume of fluid moved against a restriction,
so to maintain system pressure at the desired level, there must be some
type of restriction built into the fuel system. This restriction is
more commonly known as the fuel pressure regulator. The fuel pressure
regulator restricts the return of fuel to the tank by a calibrated
amount, maintaining system pressure at the desired level. On early
K-Jet systems, this regulator was a slide valve (also known as a push
valve) internal to the fuel distributor. Fuel pressure could be
adjusted by adding or removing shims from the valve. On later K-Jet
systems, the regulator is the conventional diaphragm type.
Control pressure (or
counter pressure) is the pressure that is metered to the top of the
fuel plunger on a K-Jet system. By changing the counter pressure, the
resistance to plunger movement is changed, allowing enrichment and
enleanment of the fuel mixture to the engine. On a car equipped with
K-Jet, this pressure is controlled by the warm-up regulator.
The warm-up regulator
only compensates for engine temperature and is therefore a rather
coarse control of fuel mixture. (Some K-Jet warm-up regulators also
have a vacuum port to help with the acceleration enrichment and
deceleration enleanment function.) Typical control pressures on a K-Jet
warm-up regulator are 55 psi with the engine at full operating
temperature and 20 to 30 psi on a cold engine. (The colder the engine,
the lower the pressure.)
A car equipped with
K-Jet Lambda also changes control pressure with a warm-up regulator
(with pressures similar to a plain K-Jet system), but also controls
lower chamber pressure in the fuel distributor by bleeding pressure
through a frequency valve. By modifying lower chamber pressure, a
change in volume of injected fuel is made, enriching or enleaning the
mixture. The frequency valve is nothing more than an electrically
duty-cycled fuel pressure regulator controlled by an on-board computer
in response to an oxygen sensor signal. This system provides a more
precise and rapid control of fuel mixture. Typical duty cycle on a
properly running engine is 45 percent to 55 percent duty and
fluctuating. A quick test of this system is to start the engine and
test the frequency valve for vibration or noise -- it should vibrate.
Also, unplugging the oxygen sensor will put the system in open loop and
fix the frequency valve at a 50 percent duty cycle.
The KE-Jet system
provides quicker response and more precise control of fuel mixture than
the K-Jet Lambda system and is the current K-Jet system in use. This
system uses a device called a differential pressure regulator to
control fuel mixture in response to both engine temperature and oxygen
sensor signals. In the KE-Jet system, counter pressure is broken down
into primary counter pressure and control counter pressure. Primary
counter pressure is the pressure applied to the top of the fuel
plunger. This pressure stays constant and is the same as system
pressure.
Control counter pressure
is modified by the differential pressure regulator and is actually the
lower chamber pressure in the fuel distributor. By modifying lower
chamber pressure, the fuel mixture can be enriched or enleaned in
response to temperature and oxygen sensor signals. Typical control
counter pressures are 4 to 7 psi less than system pressure on a fully
warmed engine and 17 to 20 psi less than system pressure on a cold
engine (typical system pressures are 5.0 to 5.5 bar or 75 to 85 psi).
The signal to the differential pressure regulator from the computer is
measured in milliamps of current. To test this signal, a DVOM must be
placed in series with the differential pressure regulator. Typical
current values are 80 milliamps cold engine (15k ohm resistor in place
of coolant temp sensor to simulate a cold engine condition); 120
milliamps during cranking (this is a crank enrich function to aid
starting); and 8 to 12 milliamps warm idle. (Note: always check service
manual for values.) These values correspond to the fuel pressures
listed. In other words, at 80 milliamps current you should show 17 to
20 psi less than system pressure.
Rest pressure is the
fuel pressure maintained in the system by the fuel accumulator after
engine shutdown. The fuel accumulator is a large spring-loaded
diaphragm that maintains a pressure of about 1.5 to 2.0 bar for 30
minutes or more after engine shutdown. This rest pressure provides for
fast restart and prevents fuel percolation or boiling (vapor lock).
Always check the service manual for the car line you are working on for
proper rest pressures and times. Typical symptoms caused by accumulator
problems are extended crank time and hard start hot.
With an understanding of
the system and the proper tools, K-Jetronic fuel system service is a
straightforward procedure that can keep your service bays full all year
long. Give me a call if you have any questions!...did this help? Let me know...dc
