Valve SUZUKI SWIFT 2000 1.G SF310 Service Workshop Manual

6
6
6-1
6A
6A1
6B
6C
6E1
6E1
6E2
6F
6F
6F1
6G
6H
6K
GENERAL INFORMATION
General Information
Maintenance and Lubrication
1A
1B
TABLE OF CONTENTS SECTION
0A
0B
7B
8
8A
8G HEATING AND AIR CONDITIONING
Heater and Ventilation
Air Conditioning (Oprional)
ENGINE
General Information and Diagnosis
(TBI for G10)
General Information and Diagnosis
(TBI for G13)
General lnformation and Diagnosis
(SFI for G13)
Engine Mechanical (G10 Engine)
Engine Mechanical
(G13 1-cam 16-valves Engine)
Engine Cooling
Engine Fuel
Engine and Emission Control System
(TBI for G10)
Engine and Emission Control System
(TBI for G13)
Engine and Emission Control System
(SFI for G13)
Ignition System (TBI for G10)
Ignition System (TBI for G13)
Ignition System (SFI for G13)
Cranking System
Charging System
Exhaust System
TRANSMISSION, CLUTCH AND
DIFFERENTIAL
Automatic Transmission
BODY ELECTRICAL SYSTEM
Wiring Diagram
IMMOBILIZER CONTROL SYSTEM
1B
0B
0A
1A
6
6B
6C
6E1
6A1
6F
6G
6H
6K
7B
8
8A
8G
6-1
6A
6E2
6F1
6
6E1
6F
NOTE:
The screen toned Section 8A is contained in WIRING DIAGRAM MANUAL mentioned in
RELATED MANUALS.

0A-22 GENERAL INFORMATION
A
ABS : Anti-Lock Brake System
ATDC : After Top Dead Center
API : American Petroleum Institute
ATF : Automatic Transmission Fluid
ALR : Automatic Locking Retractor
AC : Alternating Current
A / T : Automatic Transmission
A / C : Air Conditioning
ABDC : After Bottom Dead Center
A / F : Air Fuel Mixture Ratio
A-ELR : Automatic-Emergency Locking
Retractor
B
B+ : Battery Positive Voltage
BTDC : Before Top Dead Center
BBDC : Before Bottom Dead Center
C
CKT : Circuit
CMP Sensor : Camshaft Position Sensor
(Crank Angle Sensor, CAS)
CO : Carbon Monoxide
CPP Switch : Clutch Pedal Position Switch
(Clutch Switch, Clutch Start
Switch)
CPU : Central Processing Unit
CRS : Child Restraint System
D
DC : Direct Current
DLC : Data Link Connector (Assembly
Line Diag. Link, ALDL, Serial
Data Link, SDL)
DOHC : Double Over Head Camshaft
DOJ : Double Offset Joint
DRL : Daytime Running Light
DTC : Diagnostic Trouble Code
(Diagnostic Code)
E
EBCM : Electronic Brake Control
Module, ABS Control Module
ECM : Engine Control Module
ECT Sensor : Engine Coolant Temperature
Sensor (Water Temp. Sensor,
WTS)
EGR : Exhaust Gas Recirculation
EGRT Sensor : EGR Temperature Sensor
(Recirculated Exhaust
Gas Temp. Sensor, REGTS)
EFE Heater : Early Fuel Evaporation Heater
(Positive Temperature
Coefficient, PTC Heater)
ELR : Emergency Locking Retractor
EPS : Electronic Power Steering
EVAP : Evaporative Emission
EVAP Canister : Evaporative Emission Canister
(Charcoal Canister)
F
4WD : 4 Wheel Drive
G
GEN : Generator
GND : Ground
H
HC : Hydrocarbons
HO2S : Heated Oxygen Sensor
I
IAC Valve : Idle Air Control Valve (Idle
Speed Control Solenoid Valve,
ISC Solenoid Valve)
IAT Sensor : Intake Air Temperature Sensor
(Air temperature Sensor, ATS)
ICM : Immobilizer Control Module
IG : Ignition
ISC Actuator : Idle Speed Control Actuator
(Motor)
ABBREVIATIONS AND SYMBOLS MAY BE USED IN THIS MANUAL
ABBREVIATIONS

GENERAL INFORMATION 0A-23
L
LH : Left Hand
LSPV : Load Sensing Proportioning
Valve
M
MAF Sensor : Mass Air Flow Sensor (Air Flow
Sensor, AFS, Air Flow Meter,
AFM)
MAP Sensor : Manifold Absolute Pressure
Sensor (Pressure Sensor, PS)
Max : Maximum
MFI : Multiport Fuel Injection
(Multipoint Fuel Injection)
Min : Minimum
MIL : Malfunction Indicator Lamp
M / T : Manual Transmission
N
NOx : Nitrogen Oxides
O
OBD : On-Board Diagnostic System
(Self-Diagnosis Function)
O / D : Overdrive
OHC : Over Head Camshaft
P
PNP : Park / Neutral Position
P / S : Power Steering
PSP Switch : Power Steering Pressure Switch
(P / S Pressure Switch)
PCM : Powertrain Control Module
PCV : Positive Crankcase Ventilation
R
RH : Right Hand
S
SAE : Society of Automotive
Engineers
SDM : Sensing and Diagnostic Module
(Air Bag Controller, Air Bag
Control Module)
SFI : Sequential Multiport Fuel
Injection
SOHC : Single Over Head Camshaft
T
TBI : Throttle Body Fuel Injection
(Single-Point Fuel Injection,
SPI)
TCC : Torque Converter Clutch
TCM : Transmission Control Module
(A / T Controller, A / T Control
Module)
TP Sensor : Throttle Position Sensor
TVV : Thermal Vacuum Valve
(Thermal Vacuum Switching
Valve, TVSV, Bimetal Vacuum
Switching Valve, BVSV)
TWC : Three-Way Catalytic Converter
(Three-Way Catalyst)
2WD : 2 Wheel Drive
V
VIN : Vehicle Identification Number
VSS : Vehicle Speed Sensor
W
WU-OC : Warm Up Oxidation Catalytic
Converter
WU-TWC : Warm Up Three-Way Catalytic
Converter

0B-2 MAINTENANCE AND LUBRICATION
MAINTENANCE SCHEDULE
NORMAL CONDITION SCHEDULE
Interval:
This interval should be
judged by
This table includes services as scheduled up to 90,000 km (54,000 miles)
mileage. Beyond 90,000 km (54,000 miles), carry out the same services at
the same intervals respectively.
jg y
odometer reading or months,Km(
1,000)153045607590
whichever comes first.Miles(
1,000)91827364554
Months122436486072
1. ENGINE
1-1.Drive belt (tension,V-beltIRIRIR
damage)
V-rib belt (Flat type)––I––R
1-2.Camshaft timing beltReplace every 100,000 km (60,000 miles).
1-3.Valve lash (1.3 liter engine)–I–I–I
1-4.Engine oilVehicle with O2S (SG, SH, SJ)RRRRRR
and oil filter
Vehicle with O2S (SE, SF)
Vehicle without O2SReplace every 10,000 km (6,000 miles)
or 8 months
1-5.Engine coolant–R–R–R
1-6.Exhaust system (leakage, damage, tightness)–I–I–I
2. IGNITION SYSTEM
2-1.Spark plugsWhen unleaded
fuel is usedVehicle
without
O2S
–R–R–R
Vehicle
with O2S––R––R
When leaded fuel is usedRefer to “Severe Driving Condition” schedule.
2-2.Distributor cap and rotor (if equipped)––I––I
3. FUEL SYSTEM
3-1.Air cleaner filterPaved-roadIIRIIR
Dusty conditionRefer to “Severe Driving Condition” schedule.
3-2.Fuel lines (deterioration, leakage, damage)–I–I–I
3-3.Fuel tank––I––I
NOTES:

For Item 2-1 “spark plugs”, replace every 50,000 km if the local law requires.

For Sweden, Item 2-1, 4-1 and 4-2 should be performed by odometer reading only.

For Item 1-2 Camshaft timing belt: This belt may be replaced every 90,000 km (54,000 miles) according
to customer’s maintenance convenience.

MAINTENANCE AND LUBRICATION 0B-3
Interval:
This interval should be
judged by
This table includes services as scheduled up to 90,000 km (54,000 miles)
mileage. Beyond 90,000 km (54,000 miles), carry out the same services at
the same intervals respectively.
This interval should be judged by
odometer reading or months,Km(
1,000)153045607590g
whichever comes first.Miles(
1,000)91827364554
Months122436486072
4. EMISSION CONTROL SYSTEM
4-1.PCV (Positive Crankcase Ventilation)
ValveVehicle
without
O2S
––I––I
Vehicle
with O2S–––––I
4-2.Fuel evaporative emission control system–––––I
5. BRAKE
5-1.Brake discs and padsIIIIII
Brake drums and shoes–I–I–I
5-2.Brake hoses and pipes–I–I–I
5-3.Brake fluid–R–R–R
5-4.Brake lever and cableInspect at first 15,000 km (9,000 miles) only.
6. CHASSIS AND BODY
6-1.Clutch pedal (for manual transmission)–I–I–I
6-2.Tires/wheel discsIIIIII
6-3.Propeller shaft (4WD) and drive shafts––I––I
6-4.Suspension system–I–I–I
6-5.Steering system–I–I–I
6-6.Power steering (if equipped)IIIIII
6-7.Manual transmission oilI–R––R
6-8.Automatic transmissionFluid level–I–I–I
Fluid changeReplace every 165,000 km (99,000 miles).
Fluid hose–––R––
6-9.Rear differential oil (4WD) (R: 1st 15,000 km only)R or I–I–I–
6-10. All latches, hinges and locks–I–I–I
NOTES:

“R”: Replace or change

“I”: Inspect and correct or replace if necessary

1. Thickness gauge IN
EX
0B-6 MAINTENANCE AND LUBRICATION
Water Pump Belt Replacement
Replace belt with a new one. Refer to SECTION 6B for replacement
procedure of pump belt.
NOTE:
When replacing belt with a new one, adjust belt tension to
5 – 7 mm (0.20 – 0.27 in.).
ITEM 1-2
Camshaft Timing Belt Replacement
Replace belt with new one. Refer to SECTION 6A or 6A1 for re-
placement procedure.
CAUTION:

Do not bend or twist timing belt.

Do not allow timing belt to come into contact with oil, wa-
ter, etc.
ITEM 1-3
Valve Lash Inspection (1.3 liter engine only)
1) Remove cylinder head cover.
2) Inspect intake and exhaust valve lash and adjust as necessary.
Refer to SECTION 6A1 for valve lash inspection and adjustment
procedure.
Valve
lash
(gap)
When cold
(Coolant temperature is
15 – 25C or 59 – 77F)When hot
(Coolant temperature is
60 – 68C or
140 – 154F)
(gap)
specifi-
cation
Intake0.13 – 0.17 mm
(0.005 – 0.007 in.)0.17 – 0.21 mm
(0.007 – 0.008 in.)
cation
Exhaust0.23 – 0.27 mm
(0.009 – 0.011 in.)0.28 – 0.32 mm
(0.011 – 0.013 in.)
Special Tool
(A): 09917-18211
Tightening Torque
(a): 12 N
.m (1.2 kg-m, 8.5 lb-ft)
3) Install cylinder head cover and tighten bolts to specification.

0B-12 MAINTENANCE AND LUBRICATION
EMISSION CONTROL SYSTEM
ITEM 4-1
PCV (Positive Crankcase Ventilation) Valve Inspection
Check crankcase ventilation hoses and PCV hoses for leaks,
cracks or clog, and PCV valve (1) for stick or clog. Refer to ON-VE-
HICLE SERVICE of SECTION 6E1 or 6E2 for PCV valve checking
procedure.
ITEM 4-2
Fuel Evaporative Emission Control System Inspection
1) Visually inspect hoses for cracks, damage or excessive bends.
Inspect all clamps for damage and proper position.
2) Check EVAP canister for operation and clog, referring to SEC-
TION 6E1 or 6E2.
If a malfunction is found, repair or replace.
BRAKE
ITEM 5-1
Brake Discs, Pads, Drums and Shoes Inspection
Brake discs and pads
NOTE:
If noise is heard from brake when brake pedal is depressed,
check brake pad lining for wear. If it is worn, both right and left
brake pads should be replaced with new ones.
1) Remove wheel and caliper but don’t disconnect brake hose from
caliper.
2) Check disc brake pads and discs for excessive wear, damage
and deflection. Replace parts as necessary. For the details, refer
to SECTION 5.
3) Install caliper and wheel.
Brake drums and shoes
1) Remove wheel and brake drum.
2) Check rear brake drums and brake linings for excessive wear
and damage.
At the same time, check wheel cylinders for leakage.
Replace as necessary.
For the details, refer to SECTION 5.
3) Install brake drum and wheel.

6
ENGINE GENERAL INFORMATION AND DIAGNOSIS (TBI FOR G10) 6-1
GENERAL INFORMATION6- 3 . . . . . . . . . . . . . .
Statement on Cleanliness and Care 6- 3. . . . .
General Information on Engine Service 6- 3. .
Precaution on Fuel System Service 6- 4. . . . .
Fuel Pressure Relief Procedure 6- 5. . . . . . . .
Fuel Leakage Check Procedure 6- 5. . . . . . . .
ENGINE DIAGNOSIS6- 6 . . . . . . . . . . . . . . . . . . . General Description 6- 6. . . . . . . . . . . . . . . . . . .
On-Board Diagnostic System 6- 6. . . . . . . . . .
Precaution in Diagnosing Trouble 6- 9. . . . . . .
Engine Diagnostic Flow Table 6-10. . . . . . . . . .
Customer Problem Inspection From 6-12. . . . .
Malfunction Indicator Lamp Check 6-13. . . . . .
Diagnostic Trouble Code Check 6-13. . . . . . . .
SECTION 6
ENGINE GENERAL INFORMATION
AND DIAGNOSIS
(TBI FOR G10)
WARNING:
For vehicles equipped with Supplemental Restraint (Air Bag) System:

Service on and around the air bag system components or wiring must be performed only by an autho-
rized SUZUKI dealer. Refer to “Air Bag System Components and Wiring Location View” under “Gener-
al Description” in air bag system section in order to confirm whether you are performing service on
or near the air bag system components or wiring. Please observe all WARNINGS and “Service Precau-
tions” under “On-Vehicle Service” in air bag system section before performing service on or around
the air bag system components or wiring. Failure to follow WARNINGS could result in unintentional
activation of the system or could render the system inoperative. Either of these two conditions may
result in severe injury.

Technical service work must be started at least 90 seconds after the ignition switch is turned to the
“LOCK” position and the negative cable is disconnected from the battery. Otherwise, the system may
be activated by reserve energy in the Sensing and Diagnostic Module (SDM).
ENGINE GENERAL INFORMATION AND DIAGNOSIS (TBI for G10)6-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ENGINE GENERAL INFORMATION AND DIAGNOSIS (SFI for G13)6-1-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ENGINE MECHANICAL (G10)6A-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ENGINE MECHANICAL (G13 1 cam 16 valves)6A1-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ENGINE COOLING6B-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ENGINE FUEL6C-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ENGINE AND EMISSION CONTROL SYSTEM (TBI for G10)6E1-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
ENGINE AND EMISSION CONTROL SYSTEM (SFI for G13)6E2-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
IGNITION SYSTEM (G10 ENGINE)6F-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
IGNITION SYSTEM (G13 ENGINE)6F1-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
CRANKING SYSTEM6G-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
CHARGING SYSTEM6H-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
EXHAUST SYSTEM6K-1 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .
NOTE:
For the descriptions for vehicle without warm up three way catalytic converter (WUTWC), refer to Section
6 and 6E1 of the Service Manual mentioned in the FOREWORD of this manual.
CONTENTS

Diagnostic Trouble Code Clearance 6-14. . . . .
Diagnostic Trouble Code Table 6-15. . . . . . . . .
Fail-safe Table 6-18. . . . . . . . . . . . . . . . . . . . . . .
Visual Inspection 6-19. . . . . . . . . . . . . . . . . . . . .
Engine Basic Inspection 6-20. . . . . . . . . . . . . . .
Engine Diagnosis Table 6-22. . . . . . . . . . . . . . .
Scan Tool Data 6-29. . . . . . . . . . . . . . . . . . . . . . .
Scan Tool Data Definitions 6-31. . . . . . . . . . . . .
Inspection of ECM (PCM) and Its Circuits 6-33
Voltage Check 6-33. . . . . . . . . . . . . . . . . . . . .
Resistance Check 6-37. . . . . . . . . . . . . . . . . .
Component Location 6-38. . . . . . . . . . . . . . . . . .
Table A-1 MIL Circuit Check
(Lamp does not come on) 6-39. . . . . . . . . . . .
Table A-2 MIL Circuit Check
(Lamp remains ON) 6-40. . . . . . . . . . . . . . . . . .
Table A-3 ECM (PCM) Power and Ground
Circuit Check 6-42. . . . . . . . . . . . . . . . . . . . . . .
DTC P0105 MAP Circuit Malfunction 6-44. . . .
DTC P0110 IAT Circuit Malfunction 6-46. . . . .
DTC P0115 ECT Circuit Malfunction 6-48. . . .
DTC P0120 Throttle Position Circuit
Malfunction 6-50. . . . . . . . . . . . . . . . . . . . . . . . .
DTC P0121 Throttle Position Circuit
Range / Performance Problem 6-52. . . . . . . . .
DTC P0130 HO2S Circuit Malfunction
(Sensor-1) 6-54. . . . . . . . . . . . . . . . . . . . . . . . . .
DTC P0133 HO2S Circuit Slow
Response (Sensor-1) 6-56. . . . . . . . . . . . . . . .
DTC P0135 HO2S Heater Circuit
Malfunction (Sensor-1) 6-57. . . . . . . . . . . . . . .
DTC P0136 HO2S Circuit Malfunction
(Sensor-2) 6-59. . . . . . . . . . . . . . . . . . . . . . . . . .
DTC P0141 HO2S Heater Circuit
Malfunction (Sensor-2) 6-62. . . . . . . . . . . . . . .
DTC P0171 Fuel System Too Lean 6-64. . . . .
DTC P0172 Fuel System Too Rich 6-64. . . . . .
DTC P0300 Random Misfire Detected 6-68. . .
DTC P0301 Cylinder 1 Misfire Detected 6-68. DTC P0302 Cylinder 2 Misfire Detected 6- 68.
DTC P0303 Cylinder 3 Misfire Detected 6- 68.
DTC P0335 CKP Sensor Circuit
Malfunction 6- 72. . . . . . . . . . . . . . . . . . . . . . . . .
DTC P0340 CMP Sensor Circuit
Malfunction 6- 74. . . . . . . . . . . . . . . . . . . . . . . . .
DTC P0420 Catalyst System Efficiency
Below Threshold 6- 76. . . . . . . . . . . . . . . . . . . .
DTC P0443 Purge Control Valve Circuit
Malfunction 6- 79. . . . . . . . . . . . . . . . . . . . . . . . .
DTC P0480 Radiator Fan Control
System Malfunction 6- 80. . . . . . . . . . . . . . . . . .
DTC P0500 Vehicle Speed Sensor
Malfunction (M / T) 6- 82. . . . . . . . . . . . . . . . . . .
DTC P0500 Vehicle Speed Sensor
Malfunction (A / T) 6- 84. . . . . . . . . . . . . . . . . . .
DTC P0505 Idle Control System
Malfunction 6- 86. . . . . . . . . . . . . . . . . . . . . . . . .
DTC P0510 Closed Throttle Position
Switch Malfunction 6- 88. . . . . . . . . . . . . . . . . .
DTC P0601 Internal Control Module
Memory Check Sum Error 6- 89. . . . . . . . . . . .
DTC P1250 EFE Heater Circuit
Malfunction 6- 90. . . . . . . . . . . . . . . . . . . . . . . . .
DTC P1450 Barometric Pressure
Sensor Low / High Input 6- 92. . . . . . . . . . . . . .
DTC P1451 Barometric Pressure Sensor
Performance Problem 6- 92. . . . . . . . . . . . . . . .
DTC P1500 Engine Starter Signal
Circuit Malfunction 6- 93. . . . . . . . . . . . . . . . . . .
DTC P1510 ECM (PCM) Back-up Power
Supply Malfunction 6- 94. . . . . . . . . . . . . . . . . .
Table B-1 Fuel Injector Circuit Check 6- 96. . . .
Table B-2 Fuel Pump and Its Circuit
Check 6- 98. . . . . . . . . . . . . . . . . . . . . . . . . . . . .
Table B-3 Fuel Pressure Check 6-100. . . . . . . . .
Table B-4 A / C Signal Circuits Check 6-102. . . .
Table B-5 Power Steering Pressure
Switch Signal Circuit Check 6-103. . . . . . . . . . .
SPECIAL TOOL6-104 . . . . . . . . . . . . . . . . . . . . . . .
6-2 ENGINE GENERAL INFORMATION AND DIAGNOSIS (TBI FOR G10)

1. No.1 cylinder
2. No.2 cylinder
3. No.3 cylinder
123
ENGINE GENERAL INFORMATION AND DIAGNOSIS (TBI FOR G10) 6-3
GENERAL INFORMATION
STATEMENT ON CLEANLINESS AND CARE
An automobile engine is a combination of many machined, honed,
polished and lapped surfaces with tolerances that are measured in
the thousands of an millimeter (ten thousands of an inch).
Accordingly, when any internal engine parts are serviced, care and
cleanliness are important.
Throughout this section, it should be understood that proper clean-
ing and protection of machined surfaces and friction areas is part
of the repair procedure. This is considered standard shop practice
even if not specifically stated.

A liberal coating of engine oil should be applied to friction areas
during assembly to protect and lubricate the surfaces on initial op-
eration.

Whenever valve train components, pistons, piston rings, con-
necting rods, rod bearings, and crankshaft journal bearings are
removed for service, they should be retained in order.
At the time of installation, they should be installed in the same
locations and with the same mating surfaces as when removed.

Battery cables should be disconnected before any major work is
performed on the engine.
Failure to disconnect cables may result in damage to wire har-
ness or other electrical parts.

Throughout this manual, the four cylinders of the engine are iden-
tified by numbers; No.1 (1), No.2 (2) and No.3 (3) counted from
crankshaft pulley side to flywheel side.
GENERAL INFORMATION ON ENGINE SERVICE
THE FOLLOWING INFORMATION ON ENGINE SERVICE
SHOULD BE NOTED CAREFULLY, AS IT IS IMPORTANT IN PRE-
VENTING DAMAGE, AND IN CONTRIBUTING TO RELIABLE EN-
GINE PERFORMANCE.

When raising or supporting engine for any reason, do not use a
jack under oil pan. Due to small clearance between oil pan and
oil pump strainer, jacking against oil pan may cause it to be bent
against strainer resulting in damaged oil pick-up unit.

It should be kept in mind, while working on engine, that 12-volt
electrical system is capable of violent and damaging short cir-
cuits.
When performing any work where electrical terminals can be
grounded, ground cable of the battery should be disconnected at
battery.

Any time the air cleaner, throttle body or intake manifold is re-
moved, the intake opening should be covered. This will protect
against accidental entrance of foreign material which could follow
intake passage into cylinder and cause extensive damage when
engine is started.