Mitsubishi Montero (1998+). Manual - part 360

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

latter are the 1970’s Cadillac EFI system, early Jeep 4.0 EFI (Renix

system), and Chrysler 1984-87 TBI.

         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

controlled type drivers (explained in the next section), because they

bend upwards at this point.

         How come the difference? Because of the total circuit

resistance. Voltage controlled driver circuits have a high resistance

of 12+ ohms that slows the building of the magnetic field in the

injector. Hence, no counter voltage is built up and the line remains

flat.

         On the other hand, the current controlled driver circuit has

low resistance which allows for a rapid magnetic field build-up. This

causes a slight inductive rise (created by the effects of counter

voltage) and hence, the upward bend. You should not see that here with

voltage controlled circuits.

         Point "D" represents the electrical condition of the injector

windings. The height of this voltage spike (inductive kick) is

proportional to the number of windings and the current flow through

them. The more current flow and greater number of windings, the more

potential for a greater inductive kick. The opposite is also true. The

less current flow or fewer windings means less inductive kick.

Typically you should see a minimum 35 volts at the top of Point "D".

         If you do see approximately 35 volts, it is because a zener

diode is used with the driver to clamp the voltage. Make sure the

beginning top of the spike is squared off, indicating the zener dumped

the remainder of the spike. If it is not squared, that indicates the

spike is not strong enough to make the zener fully dump, meaning the

injector has a weak winding.

         If a zener diode is not used in the computer, the spike from

a good injector will be 60 or more volts.

         Point "E" brings us to a very interesting section.  As you

can see, the voltage dissipates back to supply value after the peak of

the inductive kick. Notice the slight hump? This is actually the

mechanical injector pintle closing. Recall that moving an iron core

through a magnetic field will create a voltage surge. The pintle is

the iron core here.

         This pintle hump at Point "E" should occur near the end of

the downward slope, and not afterwards. If it does occur after the

slope has ended and the voltage has stabilized, it is because the

pintle is slightly sticking because of a faulty injector

         If you see more than one hump it is because of a distorted

pintle or seat. This faulty condition is known as "pintle float".

         It is important to realize that it takes a good digital

storage oscilloscope or analog lab scope to see this pintle hump

clearly. Unfortunately, it cannot always be seen.

Fig. 2:  Identifying Voltage Controlled Type Injector Pattern

         INTERPRETING A CURRENT CONTROLLED PATTERN

NOTE:    Current controlled drivers are also known as "Peak and Hold"

         drivers. They typically require injector circuits

         with a total leg resistance with less than 12 ohm.

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

         circuit.

     *   See Fig. 3 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 could 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.

         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.

         Right after Point "C", something interesting happens. Notice

the trace starts a normal upward bend. This slight inductive rise is

created by the effects of counter voltage and is normal. This is

because the low circuit resistance allowed a fast build-up of the

magnetic field, which in turn created the counter voltage.

         Point "D" is the start of the current limiting, also known as

the "Hold" time. Before this point, the driver had allowed the current

to free-flow ("Peak") just to get the injector pintle open. By the

time point "D" occurs, the injector pintle has already opened and the

computer has just significantly throttled the current back. It does

this by only allowing a few volts through to maintain the minimum

current required to keep the pintle open.

         The height of the voltage spike seen at the top of Point "D"

represents the electrical condition of the injector windings. The

height of this voltage spike (inductive kick) is proportional to the

number of windings and the current flow through them. The more current

flow and greater number of windings, the more potential for a greater

inductive kick. The opposite is also true. The less current flow or

fewer windings means less inductive kick. Typically you should see a

minimum 35 volts.

         If you see approximately 35 volts, it is because a zener

diode is used with the driver to clamp the voltage. Make sure the

beginning top of the spike is squared off, indicating the zener dumped

the remainder of the spike. If it is not squared, that indicates the

spike is not strong enough to make the zener fully dump, meaning there

is a problem with a weak injector winding.

         If a zener diode is not used in the computer, the spike from