Volkswagen Corrado (1993 year). Manual - part 217

 

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Volkswagen Corrado (1993 year). Manual - part 217

 

 

WAVEFORMS - INJECTOR PATTERN TUTORIAL 

RELATIONSHIP BETWEEN DWELL & DUTY CYCLE READINGS TABLE (1)

ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

Dwell Meter (2)                             Duty Cycle Meter

1

ø

  ....................................................  1%

15

ø

  ..................................................  25%

30

ø

  ..................................................  50%

45

ø

  ..................................................  75%

60

ø

  .................................................  100%

(1) - These are just some examples for your understanding.
      It is okay to fill in the gaps.
(2) - Dwell meter on the six-cylinder scale.

ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄ

         THE TWO TYPES OF INJECTOR DRIVERS

         OVERVIEW

         There are two types of transistor driver circuits used to
operate electric fuel injectors: voltage controlled and current
controlled. The voltage controlled type is sometimes called a
"saturated switch" driver, while the current controlled type is
sometimes known as a "peak and hold" driver.
         The basic difference between the two is the total resistance
of the injector circuit. Roughly speaking, if a particular leg in an
injector circuit has total resistance of 12 or more ohms, a voltage
control driver is used. If less than 12 ohms, a current control driver
is used.
         It is a question of what is going to do the job of limiting
the current flow in the injector circuit; the inherent "high"
resistance in the injector circuit, or the transistor driver. Without
some form of control, the current flow through the injector would
cause the solenoid coil to overheat and result in a damaged injector.

         VOLTAGE CONTROLLED CIRCUIT ("SATURATED SWITCH")

WAVEFORMS - INJECTOR PATTERN TUTORIAL 

NOTE:    Never apply battery voltage directly across a low resistance
         injector. This will cause injector damage from solenoid coil
         overheating.

Fig. 1:  Injector Driver Types - Current and Voltage

WAVEFORMS - INJECTOR PATTERN TUTORIAL 

         The current controlled driver inside the computer is more
complex than a voltage controlled driver because as the name implies,
it has to limit current flow in addition to its ON-OFF switching
function. Recall, this driver typically requires injector circuits
with a total leg resistance of less than 12 ohms.
         Once the driver is turned ON, it will not limit current flow
until enough time has passed for the injector pintle to open. This
period is preset by the particular manufacturer/system based on the
amount of current flow needed to open their injector. This is
typically between two and six amps. Some manufacturers refer to this
as the "peak" time, referring to the fact that current flow is allowed
to "peak" (to open the injector).
         Once the injector pintle is open, the amp flow is
considerably reduced for the rest of the pulse duration to protect the
injector from overheating. This is okay because very little amperage
is needed to hold the injector open, typically in the area of one amp
or less. Some manufacturers refer to this as the "hold" time, meaning
that just enough current is allowed through the circuit to "hold" the
already-open injector open.
         There are a couple methods of reducing the current. The most
common trims back the available voltage for the circuit, similar to
turning down a light at home with a dimmer.
         The other method involves repeatedly cycling the circuit ON-
OFF. It does this so fast that the magnetic field never collapses and
the pintle stays open, but the current is still significantly reduced.
See the right side of Fig. 1 for an illustration.
         The advantage to the current controlled driver circuit is the
short time period from when the driver transistor goes ON to when the
injector actually opens. This is a function of the speed with which
current flow reaches its peak due to the low circuit resistance. Also,
the injector closes faster when the driver turns OFF because of the
lower holding current.

NOTE:    Never apply battery voltage directly across a low resistance
         injector. This will cause injector damage from solenoid coil
         overheating.

         THE TWO WAYS INJECTOR CIRCUITS ARE WIRED

         Like other circuits, injector circuits can be wired in one of
two fundamental directions. The first method is to steadily power the
injectors and have the computer driver switch the ground side of the
circuit. Conversely, the injectors can be steadily grounded while the
driver switches the power side of the circuit.
         There is no performance benefit to either method. Voltage
controlled and current controlled drivers have been successfully
implemented both ways.
         However, 95% percent of the systems are wired so the driver
controls the ground side of the circuit. Only a handful of systems use
the drivers on the power side of the circuit. Some examples of the

WAVEFORMS - INJECTOR PATTERN TUTORIAL 

         INTERPRETING INJECTOR WAVEFORMS

         INTERPRETING A VOLTAGE CONTROLLED PATTERN

NOTE:    Voltage controlled drivers are also known as "Saturated
         Switch" drivers. They typically require injector circuits
         with a total leg resistance of 12 ohms or more.

NOTE:    This example is based on a constant power/switched ground
         circuit.

     *   See Fig. 2 for pattern that the following text describes.

         Point "A" is where system voltage is supplied to the
injector. A good hot run voltage is usually 13.5 or more volts. This
point, commonly known as open circuit voltage, is critical because the
injector will not get sufficient current saturation if there is a
voltage shortfall. To obtain a good look at this precise point, you
will need to shift your Lab Scope to five volts per division.
         You will find that some systems have slight voltage
fluctuations here. This can occur if the injector feed wire is also
used to power up other cycling components, like the ignition coil(s).
Slight voltage fluctuations are normal and are no reason for concern.
Major voltage fluctuations are a different story, however. Major
voltage shifts on the injector feed line will create injector
performance problems. Look for excessive resistance problems in the
feed circuit if you see big shifts and repair as necessary.
         Note that circuits with external injector resistors will not
be any different because the resistor does not affect open circuit
voltage.
         Point "B" is where the driver completes the circuit to
ground. This point of the waveform should be a clean square point
straight down with no rounded edges. It is during this period that
current saturation of the injector windings is taking place and the
driver is heavily stressed. Weak drivers will distort this vertical
line.
         Point "C" represents the voltage drop across the injector
windings. Point "C" should come very close to the ground reference
point, but not quite touch. This is because the driver has a small
amount of inherent resistance. Any significant offset from ground is
an indication of a resistance problem on the ground circuit that needs
repaired. You might miss this fault if you do not use the negative
battery post for your Lab Scope hook-up, so it is HIGHLY recommended
that you use the battery as your hook-up.
         The points between "B" and "D" represent the time in
milliseconds that the injector is being energized or held open. This
line at Point "C" should remain flat. Any distortion or upward bend
indicates a ground problem, short problem, or a weak driver. Alert
readers will catch that this is exactly opposite of the current

 

 

 

 

 

 

 

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