1991 MITSUBISHI MONTERO spark










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OK   NOT OK 




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* To test secondary ignition   * Repair or replace 

system, modify a Spark Plug   damaged components 

by attaching a ground wire   as necessary 

to the body of the plug and  









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widening the gap to 1/4-3/8".

Disconnect spark plug wire 

and insert test plug. Ground 

plug, crank engine, and 

check for spark. 










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GOOD SPARK   NO SPARK 









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* If plug sparks, driveability   * Remove coil wire from the 

problem is most likely NOT   distributor and attach the 

in the ignition system.   modified spark plug. Ground 










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 the plug and crank engine 
 while checking for spark. 









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GOOD SPARK   NO SPARK 









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* If plug has a good spark,   * Proceed to the IGNITION 

the problem is in the plug   PRIMARY TROUBLE SHOOTING 

wires, distributor cap, or   CHECK CHART below in this 

rotor. Replace components   article. 

as necessary.  









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Ignition Primary Trouble Shooting Chart








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START: Visually inspect primary ignition wires for 

broken, frayed, split, or cut wires. Also check 

for loose, corroded, or disconnected connectors. 










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OK   NOT OK 




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* Check that battery voltage   * Repair or replace damaged 

is at least 11.5 volts.   components as necessary. 










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NOT OK   OK 








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* Replace or recharge the   * Check for battery voltage 

battery.   at the positive terminal of 










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 the coil. 









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High Pitched Whine Distance too great Align starter or check
During Cranking between starter that correct starter
Before Engine pinion and flywheel and flywheel are being
Fires but Engine used
Fires and Cranks
Normally









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High Pitched Distance too small between
Whine After Engine starter pinion and flywheel
Fires With Key Flywheel runout contributes
released. Engine to the intermittent nature
Fires and Cranks
Normally









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TUNE-UP TROUBLE SHOOTING - GAS ENGINE VEHICLES
NOTE: This is GENERAL information. This article is not intended
to be specific to any unique situation or individual vehicle
configuration. The purpose of this Trouble Shooting
information is to provide a list of common causes to
problem symptoms. For model-specific Trouble Shooting,
refer to SUBJECT, DIAGNOSTIC, or TESTING articles available
in the section(s) you are accessing.
BASIC SPARK PLUG TROUBLE SHOOTING CHARTS









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CONDITION POSSIBLE CAUSE CORRECTION








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Normal Spark Light Tan or Gray deposits No Action
Plug Condition
Electrode not burned or No Action
fouled
Gap tolerance not changed No Action









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Cold Fouling or Overrich air/fuel mixture Adjust air/fuel
Carbon Deposits mixture, see ENGINE
PERFORMANCE section
Faulty choke Replace choke
assembly, see ENGINE
PERFORMANCE section
Clogged air filter Clean and/or replace
air filter
Incorrect idle speed or Reset idle speed and/
dirty carburetor or clean carburetor
Faulty ignition wires Replace ignition
wiring
Prolonged operation Shut engine off
at idle during long idle
Sticking valves or worn Check valve train
valve guide seals









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Wet Fouling Worn rings and pistons Install new rings and
or Oil Deposits pistons

Excessive cylinder wear Rebore or replace
block
Excessive valve guide Worn or loose bearing
clearance









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Gap Bridged Deposits in combustion Clean combustion
chamber becoming fused chamber of deposits
to electrode









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Blistered Engine overheating Check cooling system
Electrode
Wrong type of fuel Replace with correct
fuel
Loose spark plugs Retighten spark plugs
Over-advanced ignition Reset ignition timing
timing see ENGINE PERFORMANCE









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Pre-Ignition or Incorrect type of fuel Replace with correct
Melted Electrodes fuel
Incorrect ignition timing Reset ignition timing
see ENGINE PERFORMANCE
Burned valves Replace valves
Engine Overheating Check cooling system
Wrong type of spark plug, Replace with correct
too hot spark plug, see
ENGINE PERFORMANCE









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Chipped Severe detonation Check for over-
Insulators advanced timing or
combustion
Improper gapping Re-gap spark plugs
procedure









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Rust Colored Additives in unleaded Try different fuel
Deposits fuel brand









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Water In Combus- Blown head gasket or Repair or replace
tion Chamber cracked head head or head gasket









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NOTE: Before diagnosing an electronic ignition system, ensure that
all wiring is connected properly between distributor, wiring
connector and spark plugs. Ignition problem will show up
either as: Engine Will Not Start or Engine Runs Rough.
BASIC ELECTRONIC IGNITION TROUBLE SHOOTING CHARTS









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CONDITION POSSIBLE CAUSE CORRECTION








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Engine Won't Open circuit between Repair circuit
Start distributor and bulkhead
connector
Open circuit between Repair circuit
bulkhead connector and

ignition switch
Open circuit between Repair circuit
ignition switch and
starter solenoid









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Engine Runs Fuel lines leaking or Tighten fitting,
Rough clogged remove restriction
Initial timing incorrect Reset ignition timing
see ENGINE PERFORMANCE
Centrifugal advance Repair distributor
malfunction advance
Defective spark plugs or Replace plugs or plug
wiring wiring









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Component Failure Spark arc-over on cap, Replace cap, rotor or
rotor or coil or coil
Defective pick-up coil Replace pick-up coil
Defective ignition coil Replace ignition coil
Defective vacuum unit Replace vacuum unit
Defective control module Replace control module









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BASIC ELECTRONIC IGNITION TROUBLE SHOOTING
CHARTS - USING OSCILLOSCOPE PATTERNS









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CONDITION POSSIBLE CAUSE CORRECTION








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Firing Voltage Retarded ignition timing Reset ignition
Lines are the Same, timing, see ENGINE
but Abnormally High PERFORMANCE section
Fuel mixture too lean Readjust carburetor,
see ENGINE PERFORMANCE
High resistance in coil Replace coil wire
wire
Corrosion in coil tower Clean and/or replace
terminal coil
Corrosion in distributor Clean and/or replace
coil terminal distributor cap









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Firing Voltage Fuel mixture too rich Readjust carburetor,
Lines are the Same see ENGINE PERFORMANCE
but Abnormally Low
Breaks in coil wire causing Replace coil wire
arcing
Cracked coil tower causing Replace coil
arcing
Low coil output Replace coil
Low engine compression Determine cause and

repair








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One or More, But Carburetor idle mixture Readjust carburetor,
Not All Firing not balanced see ENGINE PERFORMANCE
Voltage Lines are
Higher Than Others EGR valve stuck open Clean and/or replace
valve
High resistance in spark Replace spark plug
plug wires wires
Cracked or broken spark Replace spark plugs
plug insulator
Intake vacuum leak Repair leak
Defective spark plugs Replace spark plugs
Corroded spark plug Replace spark plugs
terminals









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One or More, But Curb idle mixture not Readjust carburetor,
Not All Firing balanced see ENGINE PERFORMANCE
Voltage Lines Are
Lower Than Others Breaks in plug wires Replace plug wires
causing arcing
Cracked coil tower causing Replace coil
arcing
Low compression Determine cause and
repair
Defective spark plugs Replace spark plugs
Corroded spark plugs Replace spark plugs









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Cylinders Not Cracked distributor cap Replace distributor
Firing terminals cap
Shorted spark plug wire Determine cause and
repair
Mechanical problem in Determine cause and
engine repair
Defective spark plugs Replace spark plugs
Spark plugs fouled Replace spark plugs









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BASIC DRIVEABILITY PROBLEMS TROUBLE SHOOTING TABLE








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CONDITION POSSIBLE CAUSE CORRECTION








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Hard Starting Binding carburetor linkage Eliminate binding
Binding choke linkage Eliminate binding
Binding choke piston Eliminate binding
Restricted choke vacuum Check vacuum lines
for blockage

Worn or dirty needle valve Clean carburetor, see
and seat ENGINE PERFORMANCE
Float sticking Readjust or replace
float see the ENGINE
PERFORMANCE section
Incorrect choke adjustment Reset choke adjustment
see ENGINE PERFORMANCE
Defective coil Replace coil
Improper spark plug gap Regap spark plugs
Incorrect ignition timing Reset ignition timing
see ENGINE PERFORMANCE









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Detonation Over-advanced ignition Reset ignition timing
timing see ENGINE PERFORMANCE
Defective spark plugs Replace spark plugs
Fuel lines clogged Clean fuel lines
EGR system malfunction Check and repair EGR
system
PCV system malfunction Repair PCV system
Vacuum leaks Check and repair
vacuum system
Loose fan belts Tighten or replace
fan belts, see ENGINE
PERFORMANCE
Restricted airflow Remove restriction
Vacuum advance malfunction Check distributor
operation









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Dieseling Binding carburetor linkage Eliminate binding
Binding throttle linkage Eliminate blinding
Binding choke linkage or Eliminate binding
fast idle cam
Defective idle solenoid Replace idle solenoid
see ENGINE PERFORMANCE
Improper base idle speed Reset idle speed, see
see ENGINE PERFORMANCE
Incorrect ignition timing Reset ignition timing
see ENGINE PERFORMANCE
Incorrect idle mixture Reset idle mixture,
setting see ENGINE PERFORMANCE









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Faulty Incorrect ignition timing Reset ignition timing
Acceleration see ENGINE PERFORMANCE

Engine cold and choke too Adjust choke and
lean allow engine to warm-
up
Defective spark plugs Replace spark plugs
Defective coil Replace coil









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Faulty Low Speed Clogged idle transfer slots Clean idle transfer
Operation slots, see FUEL
Restricted idle air bleeds Disassemble and clean
and passages carburetor, see FUEL
Clogged air cleaner Replace air filter
Defective spark plugs Replace spark plugs
Defective ignition wires Replace ignition wire
see ENGINE PERFORMANCE
Defective distributor cap Replace distributor
cap









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Faulty High Speed Incorrect ignition timing Reset ignition timing
Operation see ENGINE PERFORMANCE
Defective distributor Replace advance
centrifugal advance mechanism
Defective distributor Replace advance unit
vacuum advance
Incorrect spark plugs or Check gap and/or
plug gap replace spark plugs
Faulty choke operation Check choke and
repair as required
Clogged vacuum passages Remove restrictions
Improper size or clogged Check jet size and
main jet clean, see FUEL
Restricted air cleaner Check filter and
replace as necessary
Defective distributor cap, Replace cap, rotor or
rotor or coil coil









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Misfire at All Defective spark plugs Replace spark plugs
Speeds
Defective spark plug wires Replace spark plug
wires
Defective distributor cap, Replace cap, rotor,
rotor, or coil or coil
Cracked or broken vacuum Replace vacuum hoses
hoses

Vacuum leaks Repair vacuum leaks
Fuel lines clogged Remove restriction









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Hesitation Cracked or broken vacuum Replace vacuum hoses
hoses
Vacuum leaks Repair Vacuum leaks
Binding carburetor linkage Eliminate binding
Binding throttle linkage Eliminate binding
Binding choke linkage or Eliminate binding
fast idle cam
Improper float setting Readjust float
setting, see FUEL
Cracked or broken ignition Replace ignition
wires wires









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Rough idle, Incorrect curb idle or fast Reset idle speed, see
Missing or idle speed see ENGINE PERFORMANCE
Stalling
Incorrect basic timing Reset ignition timing
see ENGINE PERFORMANCE
Improper idle mixture Reset idle mixture,
adjustment see ENGINE PERFORMANCE
Improper feedback system Check feedback system
operation see ENGINE PERFORMANCE
Incorrect spark plug gap Reset spark plug gap,
see ENGINE PERFORMANCE
Moisture in ignition Dry components
components
Loose or broken ignition Replace ignition
wires wires
Damaged distributor cap or Replace distributor
or rotor cap or rotor
Faulty ignition coil Replace ignition coil
Fuel filter clogged or worn Replace fuel filter
Damaged idle mixture screw Replace idle mixture
screw, see FUEL
Improper fast idle cam Reset fast idle cam
adjustment adjustment, see TUNE-
see ENGINE PERFORMANCE
Improper EGR valve operation Replace EGR valve
Faulty PCV valve air flow Replace PCV valve
Choke binding or improper Reset choke or
choke setting eliminate binding