fuel FORD FESTIVA 1991 Repair Manual

TUNE-UP TROUBLE SHOOTING - GAS ENGINE VEHICLES
BASIC SPARK PLUG TROUBLE SHOOTING CHARTS
Faulty solenoid switch, switch connections or relayCheck all wiring between
relay and solenoid or replace
relay or solenoid as necessary
Broken lead or loose soldered connectionsRepair wire or wire
connections as necessary
Solenoid Plunger Vibrates When Switch is Engaged
Weak batteryCharge or replace battery as
necessary
Solenoid contacts corrodedClean contacts or replace
solenoid
Faulty wiringCheck all wiring leading to
solenoid
Broken connections inside switch coverRepair connections or replace
solenoid
Open hold-in wireReplace solenoid
Low Current Draw
Worn brushes or weakReplace brushes or brush
springs as necessary
High Pitched Whine During Cranking Before Engine Fires but Engine Fires and Cranks Normally
Distance too great between starter pinion and flywheelAlign starter or check that
correct starter and flywheel
are being used
High Pitched Whine After Engine Fires With Key released. Engine Fires and Cranks Normally
Distance too small between starter pinion and flywheelFlywheel runout contributes
to the intermittent nature
NOTE:This is GENERAL inform ation. This article is not intended to be specific to any unique situation or
individual vehicle configuration. T he purpose of this T rouble Shooting inform ation is to provide a list
of com m on causes to problem sym ptom s. For m odel-specific T rouble Shooting, refer to SUBJECT ,
DIAGNOST IC, or T EST ING articles available in the section(s) you are accessing.
CONDITION & POSSIBLE CAUSECORRECTION
Normal Spark Plug Condition
Light Tan or Gray depositsNo Action
Electrode not burned or fouledNo Action
Gap tolerance not changedNo Action
Cold Fouling or Carbon Deposits
Overrich air/fuel mixtureAdjust air/fuel mixture, see
ENGINE PERFORMANCE
section
Faulty chokeReplace choke assembly, see
ENGINE PERFORMANCE
section
Clogged air filterClean and/or replace air filter
Incorrect idle speed or dirty carburetorReset idle speed and/ or clean
carburetor
Faulty ignition wiresReplace ignition wiring
Prolonged operation at idleShut engine off during long
idle
Sticking valves or worn valve guide sealsCheck valve train
Wet Fouling or Oil Deposits
Worn rings and pistonsInstall new rings and pistons
Excessive cylinder wearRebore or replace block
Excessive valve guide clearanceWorn or loose bearing
Gap Bridged
Deposits in combustion chamber becoming fused to electrodeClean combustion chamber of
deposits
Blistered Electrode
Engine overheatingCheck cooling system
Wrong type of fuelReplace with correct fuel
Loose spark plugsRetighten spark plugs
Over-advanced ignition timingReset ignition timing see
ENGINE PERFORMANCE
Pre-Ignition or Melted Electrodes
Incorrect type of fuelReplace with correct fuel
Incorrect ignition timingReset ignition timing see
ENGINE PERFORMANCE
Burned valvesReplace valves
Engine OverheatingCheck cooling system
Wrong type of spark plug, too hotReplace with correct spark
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BASIC ELECTRONIC IGNITION TROUBLE SHOOTING CHARTS
BASIC ELECTRONIC IGNITION TROUBLE SHOOTING CHARTS - USING OSCILLOSCOPE PATTERNS
plug, see ENGINE
PERFORMANCE
Chipped Insulators
Severe detonationCheck for over-advanced
timing or combustion
Improper gapping procedureRe-gap spark plugs
Rust Colored Deposits
Additives in unleaded fuelTry different fuel brand
Water In Combustion Chamber
Blown head gasket or cracked headRepair or replace head or head
ga ske t
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.
CONDITION & POSSIBLE CAUSECORRECTION
Engine Won't Start
Open circuit between distributor and bulkhead connectorRepair circuit
Open circuit between bulkhead connector and ignition switchRepair circuit
Open circuit between ignition switch and starter solenoidRepair circuit
Engine Runs Rough
Fuel lines leaking or cloggedTigh t e n fit t in g, r e mo ve
restriction
Initial timing incorrectReset ignition timing see
ENGINE PERFORMANCE
Centrifugal advance malfunctionRepair distributor advance
Defective spark plugs or wiringReplace plugs or plug wiring
Component Failure
Spark arc-over on cap, rotor or coilReplace cap, rotor or or coil
Defective pick-up coilReplace pick-up coil
Defective ignition coilReplace ignition coil
Defective vacuum unitReplace vacuum unit
Defective control moduleReplace control module
CONDITION & POSSIBLE CAUSECORRECTION
Firing Voltage Lines are the Same, but Abnormally High
Retarded ignition timingReset ignition timing, see
ENGINE PERFORMANCE
section
Fuel mixture too leanReadjust carburetor, see
ENGINE PERFORMANCE
High resistance in coil wireReplace coil wire
Corrosion in coil tower terminalClean and/or replace coil
Corrosion in distributor coil terminalClean and/or replace
distributor cap
Firing Voltage Lines are the Same but Abnormally Low
Fuel mixture too richReadjust carburetor, see
ENGINE PERFORMANCE
Breaks in coil wire causing arcingReplace coil wire
Cracked coil tower causing arcingReplace coil
Low coil outputReplace coil
Low engine compressionDetermine cause and repair
One or More, But Not All Firing Voltage Lines are Higher Than Others
Carburetor idle mixture not balancedReadjust carburetor, see
ENGINE PERFORMANCE
EGR valve stuck openClean and/or replace valve
High resistance in spark plug wiresReplace spark plug wires
Cracked or broken spark plug insulatorReplace spark plugs
Intake vacuum leakRepair leak
Defective spark plugsReplace spark plugs
Corroded spark plug terminalsReplace spark plugs
One or More, But Not All Firing Voltage Lines Are Lower Than Others
Curb idle mixture not balancedReadjust carburetor, see
ENGINE PERFORMANCE
Breaks in plug wiresReplace plug wires causing
arcing
Cracked coil tower causing arcingReplace coil
Low compressionDetermine cause and repair
Defective spark plugsReplace spark plugs
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BASIC DRIVEABILITY PROBLEMS TROUBLE SHOOTING
Corroded spark plugsReplace spark plugs
Cylinders Not Firing
Cracked distributor cap terminalsReplace distributor cap
Shorted spark plug wireDetermine cause and repair
Mechanical problem in engineDetermine cause and repair
Defective spark plugsReplace spark plugs
Spark plugs fouledReplace spark plugs
CONDITION & POSSIBLE CAUSECORRECTION
Hard Starting
Binding carburetor linkageEliminate binding
Binding choke linkageEliminate binding
Binding choke pistonEliminate binding
Restricted choke vacuumCheck vacuum lines for
blockage
Worn or dirty needle valve and seatClean carburetor, see ENGINE
PERFORMANCE
Float stickingReadjust or replace float see
the ENGINE
PERFORMANCE section
Incorrect choke adjustmentReset choke adjustment see
ENGINE PERFORMANCE
Defective coilReplace coil
Improper spark plug gapRegap spark plugs
Incorrect ignition timingReset ignition timing see
ENGINE PERFORMANCE
Detonation
Over-advanced ignition timingReset ignition timing see
ENGINE PERFORMANCE
Defective spark plugsReplace spark plugs
Fuel lines cloggedClean fuel lines
EGR system malfunctionCheck and repair EGR system
PCV system malfunctionRepair PCV system
Vacuum leaksCheck and repair vacuum
system
Loose fan beltsTighten or replace fan belts,
see ENGINE
PERFORMANCE
Restricted airflowRemove restriction
Vacuum advance malfunctionCheck distributor operation
Dieseling
Binding carburetor linkageEliminate binding
Binding throttle linkageEliminate blinding
Binding choke linkage or fast idle camEliminate binding
Defective idle solenoidReplace idle solenoid see
ENGINE PERFORMANCE
Improper base idle speedReset idle speed, see see
ENGINE PERFORMANCE
Incorrect ignition timingReset ignition timing see
ENGINE PERFORMANCE
Incorrect idle mixture settingReset idle mixture, see
ENGINE PERFORMANCE
Faulty Acceleration
Incorrect ignition timingReset ignition timing see
ENGINE PERFORMANCE
Engine cold and choke too leanAdjust choke and allow engine
to warm-up
Defective spark plugsReplace spark plugs
Defective coilReplace coil
Faulty Low Speed Operation
Clogged idle transfer slotsClean idle transfer slots, see
FUEL
Restricted idle air bleeds and passagesDisassemble and clean
carburetor, see FUEL
Clogged air cleanerReplace air filter
Defective spark plugsReplace spark plugs
Defective ignition wiresReplace ignition wire see
ENGINE PERFORMANCE
Defective distributor capReplace distributor cap
Faulty High Speed Operation
Incorrect ignition timingReset ignition timing see
ENGINE PERFORMANCE
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Defective distributor centrifugal advanceReplace advance mechanism
Defective distributor vacuum advanceReplace advance unit
Incorrect spark plugs or plug gapCheck gap and/or replace
spark plugs
Faulty choke operationCheck choke and repair as
required
Clogged vacuum passagesRemove restrictions
Improper size or clogged main jetCheck jet size and clean, see
FUEL
Restricted air cleanerCheck filter and replace as
necessary
Defective distributor cap, rotor or coilReplace cap, rotor or coil
Misfire at All Speeds
Defective spark plugsReplace spark plugs
Defective spark plug wiresReplace spark plug wires
Defective distributor cap, rotor, or coilReplace cap, rotor, or coil
Cracked or broken vacuum hosesReplace vacuum hoses
Vacuum leaksRepair vacuum leaks
Fuel lines cloggedRemove restriction
Hesitation
Cracked or broken vacuumReplace vacuum hoses hoses
Vacuum leaksRepair Vacuum leaks
Binding carburetor linkageEliminate binding
Binding throttle linkageEliminate binding
Binding choke linkage or fast idle camEliminate binding
Improper float settingReadjust float setting, see
FUEL
Cracked or broken ignition wiresReplace ignition wires
Rough Idle, Missing or Stalling
Incorrect curb idle or fast idle speedReset idle speed, see see
ENGINE PERFORMANCE
Incorrect basic timingReset ignition timing see
ENGINE PERFORMANCE
Improper idle mixture adjustmentReset idle mixture, see
ENGINE PERFORMANCE
Improper feedback system operationCheck feedback system see
ENGINE PERFORMANCE
Incorrect spark plug gapReset spark plug gap, see
ENGINE PERFORMANCE
Moisture in ignition componentsDry components
Loose or broken ignition wiresReplace ignition wires
Damaged distributor cap or or rotorReplace distributor cap or
rotor
Faulty ignition coilReplace ignition coil
Fuel filter clogged or wornReplace fuel filter
Damaged idle mixture screwReplace idle mixture screw,
see FUEL
Improper fast idle cam adjustmentReset fast idle cam adjustment,
see TUNE- see ENGINE
PERFORMANCE
Improper EGR valve operationReplace EGR valve
Faulty PCV valve air flowReplace PCV valve
Choke binding or improper choke settingReset choke or eliminate
binding
Vacuum leakRepair vacuum leak
Improper float bowl fuel levelReset float adjustment, see
FUEL
Clogged air bleed or idle passagesClean carburetor passages, see
FUEL
Clogged or worn air cleaner filterReplace air filter
Faulty choke vacuum diaphragmReplace diaphragm, see
ENGINE PERFORMANCE
Exhaust manifold heat valve inoperativeReplace heat valve
Improper distributor spark advanceCheck distributor operation
Leaking valves or valve componentsCheck and repair valvetrain
Improper carburetor mountingRemo ve an d remo u n t
carburetor
Excessive play in distributor shaftReplace distributor
Loose or corroded wiring connectionsRepair or replace as required
Engine Surges
Improper PCV valve airflowReplace PCV valve
Vacuum leaksRepair vacuum leaks
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VACUUM PUMP - DIESEL TROUBLE SHOOTING
VACUUM PUMP (DIESEL) TROUBLE SHOOTING CHART
MANUAL TRANSMISSION
MANUAL TRANSMISSION TROUBLE SHOOTING
MANUAL TRANSMISSION/TRANSAXLE TROUBLE SHOOTING
Clogged air bleedsRemove restriction
EGR valve malfunctionReplace EGR valve
Restricted air cleaner filterReplace air filter
Cracked or broken vacuum hosesReplace vacuum hoses
Cracked or broken ignition wiresReplace ignition wires
Vacuum advance malfunctionCheck unit and replace as
necessary
Defective or fouled spark plugsReplace spark plugs
Ping or Spark Knock
Incorrect ignition timingReset ignition timing see
ENGINE PERFORMANCE
Distributor centrifugal or vacuum advance malfunctionCheck operation and replace
as necessary
Carburetor setting too leanReadjust mixture setting, see
ENGINE PERFORMANCE
Vacuum leakEliminate vacuum leak
EGR valve malfunctionReplace EGR valve
Poor Gasoline Mileage
Cracked or broken vacuumReplace vacuum hoses hoses
Vacuum leaksRepair vacuum leaks
Defective ignition wiresReplace wires
Incorrect choke settingReadjust setting, see ENGINE
PERFORMANCE
Defective vacuum advanceReplace vacuum advance
Defective spark plugsReplace spark plugs
Binding carburetor power pistonEliminate binding
Dirt in carburetor jetsClean and/or replace jets
Incorrect float adjustmentReadjust float setting, see
FUEL
Defective power valveReplace power valve, see
ENGINE PERFORMANCE
Incorrect idle speedReadjust idle speed
Engine Stalls
Improper float levelReadjust float level
Leaking needle valve and seatReplace needle valve and seat
Vacuum leaksEliminate vacuum leaks
NOTE:This is GENERAL inform ation. This article is not intended to be specific to any unique situation or
individual vehicle configuration. T he purpose of this T rouble Shooting inform ation is to provide a list
of com m on causes to problem sym ptom s. For m odel-specific T rouble Shooting, refer to SUBJECT ,
DIAGNOST IC, or T EST ING articles available in the section(s) you are accessing.
NOTE:Diesel engines m echanical diagnosis is the sam e as gasoline engines for item s such as noisy valves,
bearings, pistons, etc. T he following trouble shooting covers only item s pertaining to diesel engines.
CONDITION & POSSIBLE CAUSECORRECTION
Excessive Noise
Loose pump-to-drive assembly screwsTighten screws
Loose tube on pump assemblyTighten tube
Valves not functioning properlyReplace valves
Oil Leakage
Loose end plugTighten end plug
Bad seal crimpRemove and re-crimp
seal
NOTE:This is GENERAL inform ation. This article is not intended to be specific to any unique situation or
individual vehicle configuration. T he purpose of this T rouble Shooting inform ation is to provide a list
of com m on causes to problem sym ptom s. For m odel-specific T rouble Shooting, refer to SUBJECT ,
DIAGNOST IC, or T EST ING articles available in the section(s) you are accessing.
ConditionPossible Cause
Noisy In Forward GearsLow gear oil level, Loose bell housing bolts, Worn bearings or
gears
Clunk On Deceleration (FWD Only)Loose engine mounts, Worn inboard CV joints, Worn differential
pinion shaft, Side gear hub counterbore in case worn oversize
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GENERAL INFORMATION
T ROUBLE SHOOT ING
* PLEASE READ THIS FIRST *
ENGINE PERFORMANCE
TUNE-UP TROUBLE SHOOTING NOTE:T his article is generic in nature and all inform ation does not apply to all vehicles. For vehicle specific
inform ation, see the appropriate articles in the ENGINE PERFORMANCE category.
NOTE:T his article is generic in nature and all inform ation does not apply to all vehicles. For vehicle specific
inform ation, see the appropriate articles in the ENGINE PERFORMANCE category.
Problem & Possible CauseAction
Carbon Fouled Plugs
C l o gge d Air Fil t e rReplace Air Filter
Incorrect Idle SpeedReset Idle Speed
Faulty Ignition WiringReplace Ignition Wiring
Sticky Valves/Worn Valve SealCheck Valve Train
Fuel Injection OperationCheck Fuel Injection
Wet/Oil Fouled Plugs
Worn Rings/PistonsOverhaul/Replace Engine
Excessive Cylinder WearOverhaul/Replace Engine
Plug Gap Bridged
Combustion Chamber Carbon DepositsClean Combustion
Chamber
Blistered Electrode
Engine OverheatingCheck Cooling System
Loose Spark PlugsClean/Torque Plugs
Over-Advanced TimingReset Timing
Wrong Plug Heat RangeInstall Correct Plug
Melted Electrodes
Incorrect TimingReset Timing
Burned ValvesReplace Valves
Engine OverheatingCheck Cooling System
Wrong Plug Heat RangeInstall Correct Plug
Engine Won't Start
Loose ConnectionsCheck Connections
No PowerCheck Fuses/Battery
Loose/Worn Timing Belt/Chain/GearsCheck Belt/Chain/Gears
Engine Runs Rough
Leaky/Clogged Fuel InjectorsRepair Fuel Injectors
Leaky/Clogged Fuel LinesRepair Fuel Lines
Clogged Fuel FilterReplace Fuel Filter
Incorrect TimingReset Timing/Check
Advance
Faulty Plugs/WiresReplace Plugs/Wires
Uneven CompressionOverhaul/Replace Engine
Poor Acceleration
Incorrect Ignition TimingReset Timing
Leaky ValvesCheck Compression
Component Failure
Spark ArcingReplace Faulty Part
Defective Pick-Up CoilReplace Pick-Up Coil
Defective Ignition CoilReplace Ignition Coil
Defective Control UnitReplace Control Unit
Ignition Diagnosis By Scope Pattern
All Firing Lines Abnormally High
Retarded Ignition TimingReset Ignition Timing
Lean Air/Fuel MixtureAdjust Fuel Mixture
High Secondary ResistanceRepair Secondary
Ign it io n
All Firing Lines Abnormally Low
Rich Air/Fuel MixtureAdjust Air/Fuel Mixture
Arcing Coil WireReplace Coil Wire
Cracked CoilReplace Coil
Low Coil OutputReplace Coil
Low CompressionCheck/Repair Engine
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FUEL INJECTION TROUBLE SHOOTING
Se ve r a l High F ir in g Lin e s
Fuel Mixture UnbalancedCheck Fuel System
EGR Valve Stuck OpenClean/Replace EGR
Valve
High Plug Wire ResistanceReplace Plug Wire
Cracked/Broken PlugsReplace Plugs
Intake Vacuum LeakRepair Leak
Several Low Firing Lines
Fuel Mixture UnbalancedAdjust Fuel Mixture
Plug Wires ArcingReplace Plug Wires
Cracked Coil ArcingReplace Coil
Uneven CompressionCheck/Repair Engine
Faulty Spark PlugsReplace Plugs
Cylinders Not Firing
Cracked Distributor CapReplace Cap
Shorted Plug WiresReplace Plug Wires
Mechanical Engine FaultCheck/Repair Engine
Spark Plugs FouledReplace Plugs
Carbon Track in Distributor CapReplace Cap
Hard Starting
Defective Ignition Coil(s)Replace Coil(s)
Fouled Spark PlugsReplace Plugs
Incorrect TimingReset Ignition Timing
NOTE:T his article is generic in nature and all inform ation does not apply to all vehicles. For vehicle specific
inform ation, see the appropriate articles in the ENGINE PERFORMANCE category.
Problem & Possible CauseAction
Cold Start Valve InoperativeTest Cold Start Valve
Poor Vacuum/Electrical ConnectionRepair Connections
Contaminated FuelTest Fuel for Water/Alcohol
Bad Fuel Pump Relay/CircuitTest Relay/Wiring
Battery Voltage LowCharge/Test Battery
Low Fuel PressureTest Press. Regulator/Pump
No Distributor Reference PulseRepair Ignition System
Coolant Temp. Sensor DefectiveTest Temp. Sensor/Circuit
No Power To InjectorsCheck Injector Fuse/Relay
Hard Starting
Defective Idle Air Control (IAC)Test IAC and Circuit
EGR Valve OpenTest EGR Valve/Control
Circuit
Restricted Fuel LinesInspect/Replace Fuel Lines
Poor MAP Sensor SignalTest MAP Sensor/Circuit
Engine Stalls During Parking ManeuverCheck P.S. Press. Switch
Rough Idle
Dirty Fuel InjectorsClean/Replace Injectors
Poor MAP Sensor SignalTest MAP Sensor/Circuit
Intermittent Fuel Injector OperationCheck Harness Connectors
Erratic Vehicle Speed Sensor InputsHarness Too Close to Plug
Wires
Poor O2 Sensor SignalTest O2 Sensor/Circuit
Faulty PCV SystemCheck PCV Valve and
Hoses
Poor Acceleration
Weak Fuel PumpReplace Fuel Pump
Dirty Fuel InjectorsClean/Replace Injectors
Excessive Intake Valve DepositsClean Intake System
Poor High Speed Operation
Low Fuel Pump VolumeFaulty Fuel Pump/Filter
Poor MAP Sensor SignalTest Speed Sensor/Circuit
Acceleration Ping/Knock
Faulty EGR SystemCheck EGR Valve and
Hoses
Poor Knock Sensor SignalTest Knock Sensor/Circuit
Poor Baro Sensor SignalTest Baro Sensor/Circuit
Improper Ignition TimingAdjust Timing
Engine OverheatingCheck Cooling System
Poor Quality FuelUse Different Fuel
Carbon Build-UpDecarbon Engine
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GENERAL INFORMATION
Com puter Relearn Procedures
COMPUTER RELEARN PROCEDURES
Vehicles equipped with engine or transmission computers may require a relearn procedure after vehicle battery is disconnected. Many vehicle
computers memorize and store vehicle operation patterns for optimum driveability and performance. When vehicle battery is disconnected,
this memory is lost. The computer will use default data until new data from each key start is stored. As computer memorizes vehicle operation
for each new key start, driveability is restored. Vehicle computers may memorize vehicles operation patterns for 40 of more key starts.
Customers often complain of driveability problems during relearn stage because vehicle acts differently then before being serviced. Depending
on type and make of vehicle and how it is equipped, the following complaints (driveability problems) may exist:
Harsh Or Poor Shift Quality
Rough Or Unstable Idle
Hesitation Or Stumble
Rich Or Lean Running
Poor Fuel Mileage
These symptoms and complaints should disappear after a number of drive cycles have been memorized. To reduce the possibility of
complaints, after any service which requires battery power to be disconnected, vehicle should be road tested.
GENERIC COMPUTER RELEARN PROCEDURES
Some manufacturers identify a specific relearn procedure which will help establish suitable driveability during relearn stage. These procedures
are especially important if vehicle is equipped with and electronically controlled automatic transmission or transaxle. Always complete
procedure before returning vehicle to customer. The following general procedures are to be used if driveability problems are encountered after
power loss or battery has been disconnected. These procedures may provide an aid in eliminating these problems.
Automatic Transmission
Set parking brake, start engine in "P" or "N" position. Warm-up vehicle to normal operating temperature or until cooling fan cycles.
Allow vehicle to idle for one minute in "N" position. Select "D" and allow engine to idle for one minute.
Accelerate at normal throttle position (20-50%) until vehicle shifts into top gear.
Cruise at light to medium throttle.
Decelerate to a stop, allowing vehicle to downshift, and use brakes normally.
Process may be repeated as necessary.
Manual Transmission
Place transmission in Neutral position.
Ensure emergency brake has been set and all accessories are turned off.
Start engine and bring to normal operating temperature.
Allow vehicle to idle in Neutral for one minute.
Initial relearn is complete, and process will be completed during normal driving.
Copyr ight 2009 Mitchell Repair Information Company, LLC. All Rights Reserved.
Article GUID: A00012612
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Fig. 7: Typical Thermostatic Air Cleaner System

FUEL EVAPORATIVE SYSTEM (EVAP)
The EVAP system allows for proper fuel system ventilation while preventing fuel vapors from reaching the atmosphere. This means that vapors
must be caught and stored while the engine is off, which is when most fuel evaporation occurs. When the engine is started, these fuel vapors
can be removed from storage and burned. In most systems, storage is provided by an activated charcoal (or carbon) canister. See Fig. 8
. On a
few early systems, charcoal canisters are not used. Instead, fuel vapors are vented into the PCV system and stored inside the crankcase.
The main components of a fuel evaporation system are a sealed fuel tank, a liquid-vapor separator and vent lines to a vapor-storing canister
filled with activated charcoal. The filler cap is normally not vented to the atmosphere, but is fitted with a valve to allow both pressure and
vacuum relief.
Although a few variations do exist between manufacturers, basic operation is the same for all systems. Check for presence of vapor storage
canister or crankcase storage connections when required. Ensure required hoses, solenoids, etc., are present and connected properly. Check
for proper type fuel tank cap. Check for any non-OEM or auxiliary fuel tanks for compliance and the required number of evaporation
canisters.

Fig. 8: Typical Fuel Evaporative System

CATALYTIC CONVERTERS
Oxidation Catalyst (OC)
This type of converter is the most common. It may use pellets or monolith medium, depending upon application. See Fig. 9 . Platinum and
palladium (or platinum alone) are used as catalyst in this type of converter.
Visually check for presence of catalytic converter(s). Check for external damage such as severe dents, removed or damaged heat shields, etc.
Also check for pellets or pieces of converter in the tailpipe.
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Fig. 9: Typical Oxidation Catalytic Converter (Pellet Type) Shown; Typical Three
-Way Catalytic Converter Is Similar
Courtesy of GENERAL MOTORS CORP.
Three-Way Catalyst (TWC)
This type of converter is nearly identical to a conventional converter with the exception of the catalyst. See Fig. 9 . The TWC converter uses
rhodium, with or without platinum, as its catalyst. Rhodium helps reduce NOx emissions, as well as HC and CO.
Visually check for presence of catalytic converter(s). Also check for presence of any required air supply system for the oxidizing section of the
converter. Check for external damage such as severe dents, removed or damaged heat shields, etc. Check for pellets or pieces of converter in
the tailpipe.
Three-Way Catalyst + Oxidation Catalyst (TWC + OC)
This system contains a TWC converter and an OC converter in a common housing, separated by a small air space. See Fig. 10. The 2 catalysts
are referred to as catalyst beds. Exhaust gases pass through the TWC first. The TWC bed performs the same function as it would as a separate
device, reducing all 3 emissions. As exhaust gases leave the bed, they pass through the air space and into the second (OC) converter catalyst
bed.
Visually check for presence of catalytic converter(s). Check for external damage such as severe dents, removed or damaged heat shields, etc.
Check for pellets or pieces of converter in the tailpipe.

Fig. 10: Typical Three
-Way + Oxidation Catalytic Converter
Courtesy of GENERAL MOTORS CORP.
FILL PIPE RESTRICTOR (FR)
A fuel tank fill pipe restrictor is used to prohibit the introduction of leaded fuel into the fuel tank. Unleaded gasoline pump dispensers have a
smaller diameter nozzle to fit fuel tank of vehicle requiring the use of unleaded fuel (vehicles equipped with catalytic converter).
Visually inspect fill pipe restrictor(s) for tampering, i.e., restrictor is oversize or the flapper is non-functional. If vehicle is equipped with an
auxiliary fuel tank, ensure auxiliary fuel tank is also equipped with a fill pipe restrictor.
EXHAUST GAS RECIRCULATION (EGR) SYSTEM
Single Diaphragm EGR Valve
This type uses a single diaphragm connected to the valve by a shaft. Diaphragm is spring-loaded to keep valve closed in the absence of
vacuum. As throttle valves open and engine speed increases, vacuum is applied to the EGR vacuum diaphragm, opening the EGR valve. This
vacuum signal comes from a ported vacuum source. Variations in the vacuum signal control the amount of exhaust gas that is recirculated. See
Fig. 11
.
Verify EGR valve is present and not modified or purposely damaged. Ensure thermal vacuum switches, pressure transducers, speed switches,
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