1990 VOLKSWAGEN CORRADO width

WAVEFORMS - INJECTOR PATTERN TUTORIAL
Article Text (p. 5)
1990 Volkswagen Corrado
For Volkswagen Technical Site: http://vw.belcom.ru
Copyright © 1998 Mitchell Repair Information Company, LLC
Thursday, March 23, 2000 09:52PM
second, all measurements in between are averaged. Because a potential
voltage drop is visible for such a small amount of time, it gets
"averaged out", causing you to miss it.
Only a DVOM that has a "min-max" function that checks EVERY
MILLISECOND will catch this fault consistently (if used in that mode).
The Fluke 87 among others has this capability.
A "min-max" DVOM with a lower frequency of checking (100
millisecond) can miss the fault because it will probably check when
the injector is not on. This is especially true with current
controlled driver circuits. The Fluke 88, among others fall into this
category.
Outside of using a Fluke 87 (or equivalent) in the 1 mS "min-
max" mode, the only way to catch a voltage drop fault is with a lab
scope. You will be able to see a voltage drop as it happens.
One final note. It is important to be aware that an injector
circuit with a solenoid resistor will always show a voltage drop when
the circuit is energized. This is somewhat obvious and normal; it is a
designed-in voltage drop. What can be unexpected is what we already
covered--a voltage drop disappears when the circuit is unloaded. The
unloaded injector circuit will show normal battery voltage at the
injector. Remember this and do not get confused.
Checking Injector On-Time With Built-In Function
Several DVOMs have a feature that allows them to measure
injector on-time (mS pulse width). While they are accurate and fast to
hookup, they have three limitations you should be aware of:
* They only work on voltage controlled injector drivers (e.g
"Saturated Switch"), NOT on current controlled injector
drivers (e.g. "Peak & Hold").
* A few unusual conditions can cause inaccurate readings.
* Varying engine speeds can result in inaccurate readings.
Regarding the first limitation, DVOMs need a well-defined
injector pulse in order to determine when the injector turns ON and
OFF. Voltage controlled drivers provide this because of their simple
switch-like operation. They completely close the circuit for the
entire duration of the pulse. This is easy for the DVOM to interpret.
The other type of driver, the current controlled type, start
off well by completely closing the circuit (until the injector pintle
opens), but then they throttle back the voltage/current for the
duration of the pulse. The DVOM understands the beginning of the pulse
but it cannot figure out the throttling action. In other words, it
cannot distinguish the throttling from an open circuit (de-energized)
condition.
Yet current controlled injectors will still yield a
millisecond on-time reading on these DVOMs. You will find it is also
always the same, regardless of the operating conditions. This is
because it is only measuring the initial completely-closed circuit on-
time, which always takes the same amount of time (to lift the injector
pintle off its seat). So even though you get a reading, it is useless.
The second limitation is that a few erratic conditions can

WAVEFORMS - INJECTOR PATTERN TUTORIAL
Article Text (p. 7)
1990 Volkswagen Corrado
For Volkswagen Technical Site: http://vw.belcom.ru
Copyright © 1998 Mitchell Repair Information Company, LLC
Thursday, March 23, 2000 09:52PM
everything together it does not miss anything (though this is also a
severe weakness that we will look at later). If an injector has a
fault where it occasionally skips a pulse, the meter registers it and
the reading changes accordingly.
Let's go back to figuring out dwell/duty readings by using
injector on-time specification. This is not generally practical, but
we will cover it for completeness. You NEED to know three things:
* Injector mS on-time specification.
* Engine RPM when specification is valid.
* How many times the injectors fire per crankshaft revolution.
The first two are self-explanatory. The last one may require
some research into whether it is a bank-fire type that injects every
360ø of crankshaft rotation, a bank-fire that injects every 720ø, or
an SFI that injects every 720
ø. Many manufacturers do not release this
data so you may have to figure it out yourself with a frequency meter.
Here are the four complete steps to convert millisecond on-
time:
1) Determine the injector pulse width and RPM it was obtained
at. Let's say the specification is for one millisecond of on-time at a
hot idle of 600 RPM.
2) Determine injector firing method for the complete 4 stroke
cycle. Let's say this is a 360
ø bank-fired, meaning an injector fires
each and every crankshaft revolution.
3) Determine how many times the injector will fire at the
specified engine speed (600 RPM) in a fixed time period. We will use
100 milliseconds because it is easy to use.
Six hundred crankshaft Revolutions Per Minute (RPM) divided
by 60 seconds equals 10 revolutions per second.
Multiplying 10 times .100 yields one; the crankshaft turns
one time in 100 milliseconds. With exactly one crankshaft rotation in
100 milliseconds, we know that the injector fires exactly one time.
4) Determine the ratio of injector on-time vs. off-time in
the fixed time period, then figure duty cycle and/or dwell. The
injector fires one time for a total of one millisecond in any given
100 millisecond period.
One hundred minus one equals 99. We have a 99% duty cycle. If
we wanted to know the dwell (on 6 cylinder scale), multiple 99% times
.6; this equals 59.4
ø dwell.
Weaknesses of Dwell/Duty Meter
The weaknesses are significant. First, there is no one-to-one
correspondence to actual mS on-time. No manufacturer releases
dwell/duty data, and it is time-consuming to convert the mS on-time
readings. Besides, there can be a large degree of error because the
conversion forces you to assume that the injector(s) are always firing
at the same rate for the same period of time. This can be a dangerous
assumption.
Second, all level of detail is lost in the averaging process.
This is the primary weakness. You cannot see the details you need to
make a confident diagnosis.

WAVEFORMS - INJECTOR PATTERN TUTORIAL
Article Text (p. 8)
1990 Volkswagen Corrado
For Volkswagen Technical Site: http://vw.belcom.ru
Copyright © 1998 Mitchell Repair Information Company, LLC
Thursday, March 23, 2000 09:52PM
Here is one example. Imagine a vehicle that has a faulty
injector driver that occasionally skips an injector pulse. Every
skipped pulse means that that cylinder does not fire, thus unburned O2
gets pushed into the exhaust and passes the O2 sensor. The O2 sensor
indicates lean, so the computer fattens up the mixture to compensate
for the supposed "lean" condition.
A connected dwell/duty meter would see the fattened pulse
width but would also see the skipped pulses. It would tally both and
likely come back with a reading that indicated the "pulse width" was
within specification because the rich mixture and missing pulses
offset each other.
This situation is not a far-fetched scenario. Some early GM
3800 engines were suffering from exactly this. The point is that a
lack of detail could cause misdiagnosis.
As you might have guessed, a lab scope would not miss this.
RELATIONSHIP BETWEEN DWELL & DUTY CYCLE READINGS TABLE (1)ÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄÄDwell 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
Article Text (p. 9)
1990 Volkswagen Corrado
For Volkswagen Technical Site: http://vw.belcom.ru
Copyright © 1998 Mitchell Repair Information Company, LLC
Thursday, March 23, 2000 09:52PM
The voltage controlled driver inside the computer operates
much like a simple switch because it does not need to worry about
limiting current flow. Recall, this driver typically requires injector
circuits with a total leg resistance of 12 or more ohms.
The driver is either ON, closing/completing the circuit
(eliminating the voltage-drop), or OFF, opening the circuit (causing a
total voltage drop).
Some manufacturers call it a "saturated switch" driver. This
is because when switched ON, the driver allows the magnetic field in
the injector to build to saturation. This is the same "saturation"
property that you are familiar with for an ignition coil.
There are two ways "high" resistance can be built into an
injector circuit to limit current flow. One method uses an external
solenoid resistor and a low resistance injector, while the other uses
a high resistance injector without the solenoid resistor. See the left
side of Fig. 1.
In terms of injection opening time, the external resistor
voltage controlled circuit is somewhat faster than the voltage
controlled high resistance injector circuit. The trend, however, seems
to be moving toward use of this latter type of circuit due to its
lower cost and reliability. The ECU can compensate for slower opening
times by increasing injector pulse width accordingly.
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

WHEEL ALIGNMENT THEORY/OPERATION
Article Text (p. 3)
1990 Volkswagen Corrado
For Volkswagen Technical Site: http://vw.belcom.ru
Copyright © 1998 Mitchell Repair Information Company, LLC
Thursday, March 23, 2000 09:53PM
positive. This creates a trailing action on front wheels. When axis is
tilted forward, caster is negative, causing a leading action on front
wheels.Fig. 4: Determining Caster Angle
TOE-IN ADJUSTMENT
Toe-in is the width measured at the rear of the tires
subtracted by the width measured at the front of the tires at about
spindle height. A positive figure would indicate toe-in and a negative
figure would indicate toe-out. If the distance between the front and
rear of the tires is the same, toe measurement would be zero. To
adjust:
1) Measure toe-in with front wheels in straight ahead
position and steering wheel centered. To adjust toe-in, loosen clamps
and turn adjusting sleeve or adjustable end on right and left tie
rods. See Figs. 2 and 5.
2) Turn equally and in opposite directions to maintain
steering wheel in centered position. Face of tie rod end must be
parallel with machined surface of steering rod end to prevent binding.
3) When tightening clamps, make certain that clamp bolts are
positioned so there will be no interference with other parts
throughout the entire travel of linkage.Fig. 5: Wheel Toe-In (Dimension A Less Dimension B)
TOE-OUT ON TURNS
1) Toe-out on turns (turning radius) is a check for bent or
damaged parts, and not a service adjustment. With caster, camber, and