ISUZU TROOPER 1995 Workshop Manual

ENGINE DIAGNOSIS 6-3
HARD STARTING
1. Starting motor does not turn over
Trouble shooting procedure
Turn on headlights and starter switch.
Condition Possible cause Correction
Headlights go out or dim Battery run down or under charged Recharge or replace battery
considerably
Terminals poorly connected Clean battery posts and
terminals and connect properly
Starting motor coil circuit shorted Overhaul or replace
Starting motor defective
Headlights stay
bright Starting motor circuit open Refer to Section 6D
Starting
motor coil open Replace
2. Ignition trouble -Starting motor turns over but engine does not start
Spark Test
Disconnect a high tension cable from any spark plug. Connect the spark plug tester J-26792 (ST-1 25).
start the engine, and check if a spark is generated in the spark plug tester.
Before starting the engine, make sure
that the spark plug tester is properly grounded. To avoid
electrical shock, do not touch the high tension cable while the engine is running.
Condition Possible cause Correction
Spark jumps across gap
Spark plug defective Clean, adjust spark gap or
replace
Ignition
timing incorrect Refer to Section 6E2
Fuel not reaching fuel injector(s) or Refer to item 3
engine (Trouble
in
fuel system)
Valve
timing incorrect Adjust
Engine
lacks compression Refer to item 4
(Engine
lacks compression)
No sparking takes
place Spark plug wire disconnected or broken Connect properly or replace
Electronic Ignition System with module Replace
Poor connections in engine harness
Correct
Engine Control
Module cable Correct or replace
disconnected or defective
3. Trouble in fuel system
Condition Possible cause Correction
Starting motor turns over and
Fuel tank empty Fill
spark occurs but engine does
not start. Water in fuel system Clean
Fuel filter clogged Replace filter
Fuel pipe clogged Clean or replace
Fuel pump defective
Replace
Fuel
pump circuit open Correct or replace
Evaporative Emission Control System Correct or replace
circuit clogged
Multipart Fuel Injection System faulty Refer to "Electronic Fuel
Injection"
section

6-4 ENGINE DIAGNOSIS
HARD STARTING (Cont'd)
4. Engine lacks compression
Condition Possible cause
Spark plug loosely fitted or spark plug
gasket defective
Valve timing incorrect
Cylinder head gasket defective
Valve incorrectly seated
Valve stem seized
Valve spring weakened
Cylinder or piston rings worn
Piston ring seized
ENGINE COMPRESSION TEST
PROCEDURE
1. Start and run the engine until the engine reaches
normal operating temperature.
2. Turn the engine off.
3. Remove all the spark plugs.
4. Remove ignition coil fuse (15A) and disable the
ignition system.
5. Remove the fuel pump relay from the relay and
fuse box.
6. Engage the starter and check that the cranking
speed is approximately
300 rpm.
7. Install cylinder compression gauge into spark plug
hole.
8. With the throttle valve opened fully, keep the
starter engaged
until the compression gage
needle reaches the
maximum level. Note the
reading.
9. Repeat the test with each cylinder.
If
the compression pressure obtained falls below the
limit, engine overhaul is necessary.
Limit; 883
kPa (128 psi) Correction
Tighten
to specified torque or
replace gasket
Adjust
Replace gasket
Lap
valve
Replace valve
and valve guide
Replace
Overhaul engine
Overhaul engine.

ENGINE DIAGNOSIS 6-5
ROUGH ENGINE IDLING OR ENGINE STALLING
Condition Possible cause Correction
Trouble in fuel
Idle air control valve defective Replace
injection system
Throttle shutting
off incomplete Correct or replace
Throttle position sensor circuit open
or shorted Correct or replace
Fuel injector circuits open or shorted Correct or replace
Fuel injectors damaged
Replace
Fuel pump relay defective Replace
Manifold Absolute Pressure Sensor
cable Correct or replace
disconnected
or broken
Manifold Absolute Pressure Sensor defective
Replace
Engine Coolant Temperature Sensor cable Correct
or replace
disconnected
or broken
Engine Coolant Temperature Sensor defective
Replace
Intake Air Temperature sensor cable Correct or replace
disconnected
or broken
Intake Air Temperature sensor defective
Replace
Knock Sensor
(KS) circuits open or shorted
Correct or replace
(DOHC only)
KS defective (DOHC only) Replace
KS Module circuits open or ground
Correct or replace
(DOHC only)
KS Module defective (DOHC only) Replace
Vehicle Speed Sensor circuit open or shorted
Correct or replace
Vehicle Speed Sensor defective
Replace
Trouble in emission
Engine Control Module defective
Replace
control system
Exhaust Gas Recirculation
Valve faulty
Replace
Back Pressure Transducer defective
Replace
Vacuum Switch Valve (VSV); EGR circuit
Correct
open
VSV; EGR defective Replace
Canister purge
VSV circuit open
Correct
VSV; canister circuit open
Correct
VSV; canister defective
Replace
Evaporative Emission Canister Purge control
Replace
valve defective
Trouble in ignition system
Refer
to Hard Start
Troubleshooting Guide
Others Engine lacks compression
Refer to Hard Start
Troubleshooting Guide
Valve incorrectly seated
Lap valve
Air Cleaner Filter clogged
Replace filter element
Valve timing incorrect
Readjust
Idle air control valve broken
Replace
Fast
idle solenoid defective
Replace
Positive Crankcase Ventilation valve defective
or Replace
clogged

6-6 ENGINE DIAGNOSIS
ROUGH ENGINE RUNNING
Complaint
Faulty parts Possible cause Correction
Engine misfires Ignition coil
Coil layer shorted Replace
regularly
high-tension Primary lead wire broken leakage due
Correct cables to defective insulator
Spark plugs
Fouling Clean
or install hotter type
plug
Insulator
nose leaking Replace
Fuel
injectors Fuel injector(s) defective Replace
Dropping register defective Replace
Engine Control
Faulty Replace
Module
Engine knocks Spark plugs
Spark plugs running too hot Install colder type spark
regularly
plugs
Engine Control Faulty
Replace
Module
Engine lacks Spark plugs
Fouled Clean
power Multipart Fuel
Fuel injectors defective Replace
Injection Manifold Absolute Pressure (MAP)
Correct or replace system Sensor or Manifold Absolute Pressure
Sensor
circuit defective
Engine
Coolant Temperature Sensor or Correct or replace
Engine Coolant Temperature Sensor
circuit dcefective
Engine
Control Module faulty Replace
Intake
Air Temperature Sensor or Intake
Air Temperature Sensor circuit Correct or replace
defective
Throttle Position Sensor or Throttle Correct or replace
Position Sensor
circuit defective
Knock
Sensor or Knock Sensor circuits Correct or replace
defective (DOHC only)
Knock Sensor Module or Knock Sensor Correct or replace .
Module
circuits defective (DOHC only)
•

ENGINE DIAGNOSIS 6-7
HESITATION
Condition Possible cause Correction
Hesitation on Throttle
Position Sensor adjustment incorrect Replace
throttle
acceleration valve
assembly
Throttle Position Sensor circuit open
or shorted Correct
or replace
Excessive play in accelerator linkage
Adjust or replace
Manifold Absolute
Pressure (MAP) Sensor circuit open or shorted Correct or replace
MAP Sensor defective Replace
Intake Air
Temperature (IAT) Sensor circuit open or shorted Correct or replace
Knock Sensor
(KS) Circuit open or shorted (DOHC only) Correct or replace
KS defective (DOHC only) Replace
KS Module circuits open or shorted (DOHC only) Correct or replace
KS Module defective (DOHC only) Replace
IAT Sensor defective Replace
Hesitation at
Fuel pressure
too low
high speeds
Fuel tank strainer clogged Clean or replace
Fuel pipe clogged
Clean or replace
Fuel filter clogged
Replace
Defective fuel
pump system Check and replace
Fuel Pressure Control Valve leaking Replace
Fuel injector
not working normally
Power supply or ground circuit for Multipart Fuel Injection Check and correct or
System shorted or open
replace
Distributor defective Replace
Cable of Multipart Fuel Injection System disconnected or defective Correct or replace
Engine Control Module defective Replace
Throttle Position Sensor circuit open
or shorted Correct or replace
Throttle Position Sensor defective Replace
Engine Coolant Temperature Sensor circuit open
or shorted Correct or replace
Engine Coolant Temperature Sensor defective Replace
MAP Sensor cable open
or shorted Correct or replace
MAP Sensor defective
Replace
IAT Sensor circuit open or shorted
Correct or replace
IAT Sensor defective Replace
KS Circuit open or shorted (DOHC only)
Correct or replace
KS defective (DOHC only) Replace
KS Module circuit open or shorted (DOHC only) Correct or replace
KS Module defective (DOHC only) Replace
Throttle valve
not wide opened
Check and correct or
replace
Air Cleaner Filter clogged
Replace filter element
Power supply voltage
too low Check and correct or
replace

6-8 ENGINE DIAGNOSIS
ENGINE LACKS POWER
Condition
Possible cause Correction
Trouble in fuel system Fuel Pressure Control Valve not Replace
working normally
Fuel
injector clogged Clean or replace
Fuel
pipe clogged Clean
Fuel filter clogged
or fouled Replace
Fuel
pump drive circuit not working Correct or replace
normally
Fuel tank not sufficiently breathing due Clean or replace
to clogged Evaporative Emission
Control System circuit
Water in
fuel system Clean
Inferior quality fuel
in fuel system Use fuel of specified octane
rating
Engine
Control Module supplied poor Correct circuit
voltage
Throttle
Position Sensor cable Correct or replace
disconnected or broken
Throttle Position Sensor defective Replace
Manifold Absolute
Pressure Sensor not Replace
working normally
Intake Air Temperature Sensor not Replace
working normally
Engine Coolant Temperature Sensor Correct or replace
circuit open or shorted
Engine
Coolant Temperature Sensor Replace
defective
Engine
Control Module defective Replace
Trouble
in intake or exhaust Air Cleaner Filter clogged Replace filter element
system Trouble in Induction air control valve Correct or replace
system (DOHC)
Air duct kinked or flattened Correct or replace
Ignition failure
Refer to Hard Start
Troubleshooting Guide
Heat range
of spark plug inadequate Install spark plugs of adequate
heat range
Electronic Ignition System with module Replace
•

ENGINE DIAGNOSIS 6-9
ENGINE LACKS POWER (Cont'd)
Condition Possible cause Correction
Engine overheating
Level of Engine Coolant too low Replenish
Thermo switch or fan motor defective Replace
Thermostat defective Replace
Engine
Coolant pump defective Correct or replace
Radiator clogged
Clean or replace
Radiator
filler cap defective Replace
Level
of oil in engine crankcase too low Change or replenish
or
wrong oil engine
Resistance in exhaust system
Clean exhaust system or
increased replace
defective parts
Throttle Position Sensor adjustment Adjust
Wide Open Throttle
incorrect switch setting
Throttle Position Sensor circuit open
or Correct or replace
shorted
Cylinder head gasket damaged Replace
Engine overcooling
Radiator
overcooling Install cover
in front of
radiator
Thermostat defective Replace
(Use a thermostat set
to open at a2·c (180.F))
Engine
lacks compression Refer to Hard Start
Others Tire inflation pressure
abnormal Adjust to recommend
pressures
Brake drag Adjust
Clutch slipping Adjust or replace
Level
of oil in engine crankcase too Correct level of engine oil
high
Exhaust Gas
Recirculation Valve Replace
defective
Back pressure transducer defective
Replace

6-10 ENGINE DIAGNOSIS
ENGINE
NOISY
Abnormal engine noise often consists of various noises originating in rotating parts, sliding parts and
other moving parts
of the engine. It is, therefore, advisable to locate the source of noise systematically.
Condition
Possible cause Correction
Noise from crank journals or Oil clearance increased due to worn Replace crank bearings and
from crank bearings
crank journals
or crank bearings crankshaft or regrind
(Faulty crank journals and
crankshaft and
install the over
crank bearings
usually make
size bearing
dull noise that becomes more Crankshaft out of round
Replace crank bearings and
evident when accelerating)
crankshaft
or regrind
crankshaft and
install the over
size bearing
Crank bearing seized Replace crank bearings and
crankshaft or regrind
crankshaft and
install the over
size bearing
Troubleshooting Procedure
Short out each spark plug in sequence using insulated sparkplug wire removers. Locate cylinder with
defective bearing by listening for abnormal noise that stops when spark plug is shorted out.
Condition
Possible cause Correction
Noise from connecting-rods or Bearing or crankshaft pin worn Replace connecting-rod
from connecting-rod bearings
bearings and crankshaft or
(Faulty connecting-rods or regrind-crankshaft and install
connecting-rod bearings
the over size bearing
usually make an abnormal
Crankpin out of round Replace
connecting-rod
noise slightly higher than the
bearings and crankshaft
or crank bearing noise, which regrind-crankshaft and install becomes more evident when the over size bearing
engine is accelerated)
Connecting-rod bent
Correct or replace
Connecting-rod bearing seized Replace
connecting-rod
bearings and crankshaft
or
regrind-crankshaft and install
the over size bearing
Troubleshooting Procedure
Abnormal noise stops when the spark plug on the cylinder with defective part is shorted out.
Condition
Possible cause Correction
Piston and cylinder Piston clearance increased due to Replace piston and cylinder
(Faulty piston or cylinder
cylinder
wear body
usually makes a combined Piston seized Replace piston and cylinder
mechanical thumping noise body which increases when engine Piston ring broken Replace piston and cylinder
is suddenly accelerated but
diminishes gradually as the body
engine warms up) Piston defective Replace pistons and others
Troubleshooting Procedure
Short out each spark plug and listen for change in engine noise.
Condition
Possible cause Correction
Piston pin noise Piston pin or piston pin hole worn Replace piston, piston pin and
(Piston makes noise each time connecting-rod assy
it goes up and down)
Troubleshooting Procedure
The slapping sound stops when spark plug on bad cylinder is shorted out.
•

ENGINE DIAGNOSIS 6-11
ENGINE NOISY (Cont'd)
Condition Possible cause Correction
Timing belt noise
Timing belt tension is incorrect Replace pusher or adjust the
ajust
pulley or replace timing
belt
Tensioner bearing defective Replace
Timing belt defective Replace
Timing wheels defective Replace
Timing belt comes in contact with Replace timing belt and timing
timing cover
cover
Valve noise Valve clearance incorrect Replace HLA
Valve and valve guide seized Replace valve and valve guide
Valve spring broken Replace
Valve
seat off-positioned
Correct
Crankshaft noise
Crankshaft end
play excessive (noise Replace thrust bearing
occurs
when clutch is engaged)
Engine knocking
Preignition due
to use of spark plugs of Install Spark Plugs of adequate
inadequate heat range
heat range
Carbon deposits in combustion
Clean
chambers
Fuel too low in octane rating Replace fuel
Wide Open Throttle enrichment system
Refer to Section 6E2
failure
Selection
of transmission gear incorrect Caution operator of incorrect
gear
selection
Engine overheating
Refer to "Engine Lacks Power"
Others Water
pump defective Replace
Drive belt slipping Adjust tension of drive belt or
replace drive belt

6-12 ENGINE DIAGNOSIS
ABNORMAL COMBUSTION
Condition
Possible cause Correction
Trouble in fuel Fuel pressure control valve defective Replace
injection system
Fuel filter clogged
Replace
Fuel pump clogged Clean or replace
Fuel tank
or fuel pipe clogged Clean or replace
Fuel injector clogged Clean or replace
Fuel
pump relay defective
Replace
Power supply cable for fuel pump loosely connected or Reconnect, correct or
defective
replace
Manifold Absolute
Pressure Sensor circuit open or shorted Correct or replace
Manifold Absolute
Pressure Sensor defective Replace
Engine Coolant Temperature
(ECT) Sensor circuit open or Correct or replace
shorted
ECT Sensor defective
Replace
Throttle
Position Sensor adjustment incorrect Replace throttle valve
Throttle
Position Sensor defective
Replace
Throttle
Position Sensor connector loosely connected Reconnect
Vehicle Speed Sensor cable loosely connected or Correct or replace
defective
Vehicle Speed Sensor loosely fixed Fix tightly
Vehicle Speed Sensor in wrong contact or defective Replace
Engine Control Module cable
loosely connected or Correct or replace
defective
Trouble in emission
Heated
Oxygen Sensor circuit open Correct or replace
control system
Heated
Oxygen Sensor defective Replace
Vacuum Switch
Valve (VSV); Replace
Exhaust Gas Recirculation defective
Signal vacuum hose loosely fitted or defective Correct or replace
Exhaust Gas Recirculation
Valve defective Replace
Back
Pressure Transducer defective Replace
ECT Sensor circuit open or shorted Correct or replace
ECT Sensor defective Replace
Pressure Control Valve (PCV) and hose clogged Correct or replace
Evaporator system
Refer
to Section 6E
Trouble in ignition
Refer to "Engine
system Lacks
Power"
Trouble in cylinder
Carbon deposits in combustion chamber Remove carbon
head parts
Carbon deposit on valve,
valve seat and valve guide
Remove carbon
•