1991 MITSUBISHI MONTERO fuel

the types of injector circuits that your noid lights are designed for.
There are three. They are:
* Systems with a voltage controlled injector driver. Another
way to say it: The noid light is designed for a circuit with
a "high" resistance injector (generally 12 ohms or above).
* Systems with a current controlled injector driver. Another
way to say it: The noid light is designed for a circuit with
a low resistance injector (generally less than 12 ohms)
without an external injector resistor.
* Systems with a voltage controlled injector driver and an
external injector resistor. Another way of saying it: The
noid light is designed for a circuit with a low resistance
injector (generally less than 12 ohms) and an external
injector resistor.
NOTE: Some noid lights can meet both the second and third
categories simultaneously.
If you are not sure which type of circuit your noid light is
designed for, plug it into a known good car and check out the results.
If it flashes normally during cranking, determine the circuit type by
finding out injector resistance and if an external injector resistor
is used. You now know enough to identify the type of injector circuit.
Label the noid light appropriately.
Next time you need to use a noid light for diagnosis,
determine what type of injector circuit you are dealing with and
select the appropriate noid light.
Of course, if you suspect a no-pulse condition you could plug
in any one whose connector fit without fear of misdiagnosis. This is
because it is unimportant if the flashing light is dim or bright. It
is only important that it flashes.
In any cases of doubt regarding the use of a noid light, a
lab scope will overcome all inherent weaknesses.
OVERVIEW OF DVOM
A DVOM is typically used to check injector resistance and
available voltage at the injector. Some techs also use it check
injector on-time either with a built-in feature or by using the
dwell/duty function.
There are situations where the DVOM performs these checks
dependably, and other situations where it can deceive you. It is
important to be aware of these strengths and weaknesses. We will cover
the topics above in the following text.
Checking Injector Resistance
If a short in an injector coil winding is constant, an
ohmmeter will accurately identify the lower resistance. The same is
true with an open winding. Unfortunately, an intermittent short is an
exception. A faulty injector with an intermittent short will show
"good" if the ohmmeter cannot force the short to occur during testing.
Alcohol in fuel typically causes an intermittent short,
happening only when the injector coil is hot and loaded by a current
high enough to jump the air gap between two bare windings or to break
down any oxides that may have formed between them.
When you measure resistance with an ohmmeter, you are only
applying a small current of a few milliamps. This is nowhere near
enough to load the coil sufficiently to detect most problems. As a
result, most resistance checks identify intermittently shorted
injectors as being normal.
There are two methods to get around this limitation. The
first is to purchase an tool that checks injector coil windings under

full load. The Kent-Moore J-39021 is such a tool, though there are
others. The Kent-Moore costs around $240 at the time of this writing
and works on many different manufacturer's systems.
The second method is to use a lab scope. Remember, a lab
scope allows you to see the regular operation of a circuit in real
time. If an injector is having an short or intermittent short, the lab
scope will show it.
Checking Available Voltage At the Injector
Verifying a fuel injector has the proper voltage to operate
correctly is good diagnostic technique. Finding an open circuit on the
feed circuit like a broken wire or connector is an accurate check with
a DVOM. Unfortunately, finding an intermittent or excessive resistance
problem with a DVOM is unreliable.
Let's explore this drawback. Remember that a voltage drop due
to excessive resistance will only occur when a circuit is operating?
Since the injector circuit is only operating for a few milliseconds at
a time, a DVOM will only see a potential fault for a few milliseconds.
The remaining 90+% of the time the unloaded injector circuit will show
normal battery voltage.
Since DVOMs update their display roughly two to five times a
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

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)









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Dwell Meter (2) Duty Cycle Meter
1
.................................................... 1%
15 .................................................. 25%
30 .................................................. 50%
45 .................................................. 75%
60 ................................................. 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.









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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")
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

\003
WHEEL A LIG NM EN T T H EO RY/O PER ATIO N
1991 M it s u bis h i M onte ro
GENERAL INFORMATION
Wheel Alignment Theory & Operation
ALL MODELS
* PLEASE READ THIS FIRST *
NOTE: This article is intended for general information purposes
only. This information may not apply to all makes and models.
PRE-ALIGNMENT INSTRUCTIONS
GENERAL ALIGNMENT CHECKS
Before adjusting wheel alignment, check the following:
* Each axle uses tires of same construction and tread style,
equal in tread wear and overall diameter. Verify that radial
and axial runout is not excessive. Inflation should be at
manufacturer's specifications.
* Steering linkage and suspension must not have excessive play.
Check for wear in tie rod ends and ball joints. Springs must
not be sagging. Control arm and strut rod bushings must not
have excessive play. See Fig. 1.
Fig. 1: Checking Steering Linkage
* Vehicle must be on level floor with full fuel tank, no
passenger load, spare tire in place and no load in trunk.
Bounce front and rear end of vehicle several times. Confirm

WIR IN G D IA G RAM S

1991 M it s u bis h i M onte ro
1991 Wiring Diagrams
Mitsubishi
Montero
IDENTIFICATION
COMPONENT LOCATION MENU
COMPONENT LOCATIONS TABLE








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Component Figure No. (Location)
A/C RELAYS .......................... 4 (C 12), 4 (A-B 15)
A/C SYSTEM ................................. 4 (A-C 12-15)
ALTERNATOR ................................... 1 (B-C 1-2)
ALTERNATOR RELAY ............................... 1 (C 1-2)
AUTO FREE-WHEELING HUB CONTROL UNIT ............. 3 (D 11)
BACK DOOR LOCK SW ............................... 7 (B 27)
BACK-UP LT SW (M/T) ............................. 7 (A 26)
BATTERY .......................................... 1 (A 1)
BLOWER SWITCH ................................. 4 (A-B 12)
BUZZER .......................................... 5 (E 17)
CARGO LIGHT ..................................... 6 (A 23)
CIG LIGHTER ..................................... 3 (E 11)
CLOCK ........................................... 3 (E 11)
COLUMN SW ..................................... 5 (A-E 19)
CRUISE CONTROL SYSTEM ...................... 4 (D-E 13-15)
DEFOGGER ...................................... 7 (C-D 27)
DIAG CONNECTION .................................. 2 (E 7)
DIMMER CONTROL SWITCH ............................ 3 (E 8)
DIR FLASHER ..................................... 5 (C 16)
DIR SWITCH ...................................... 5 (C 19)
DOME LT ............................... 6 (A 23), 7 (A 24)
DOOR LOCK SYSTEM ........................... 6 (D-E 21-23)
DOOR SWITCHES ......................... 5 (D 17), 6 (C 23)
FRONT WIPER SYSTEM ........................... 5 (A 16-17)
FUEL GAUGE UNIT ................................. 6 (C 22)
FUEL PUMP ........................................ 2 (C 4)
FUSE BLOCK .................................... 3 (C 9-10)
HAZARD FLASHER .................................. 5 (C 16)
HAZARD SW ....................................... 5 (B 16)
HEAD LIGHT WASHER RELAY ....................... 5 (C-D 17)
HEATER RELAY .................................... 4 (A 12)
HORN SWITCH ..................................... 5 (E 19)
IGNITION COIL .................................... 2 (E 4)
IGNITION SW ..................................... 3 (A 11)
ILLUMINATION LIGHTS ............................ 3 (D-E 8)
INHIBITOR SW ..................................... 3 (A 9)
INSTRUMENT CLUSTER ............................ 6 (A-D 20)
KEY REMINDER SW ................................. 5 (E-17)
LIGHT CONTROL RELAY ............................. 5 (E 19)
LIGHT SWITCH .................................... 5 (D 19)
MAIN FUSE LINKS ................................ 1 (A 1-2)
METER UNIT ...................................... 6 (E 20)
MPI CONTROL RELAY ................................ 2 (B 4)
MPI CONTROL UNIT ............................... 2 (A 4-7)
NOISE FILTER ..................................... 2 (E 6)
OVERDRIVE CONTROL RELAY .......................... 3 (A 8)