Suzuki Engine 2002 GRAND VITARA SQ420 Service Manual page 43

6-38 ENGINE GENERAL INFORMATION AND DIAGNOSIS (G16/J20 ENGINES)
Condition
Surges
(Engine power varia-
tion under steady
throttle or cruise.
Feels like the vehicle
speeds up and down
with no change in the
accelerator pedal.)
Excessive detonation
(The engine makes
sharp metallic
knocks that change
with throttle opening.
Sounds like pop corn
popping.)
Possible Cause
Ignition system out of order.
• Defective spark plug (excess carbon
deposits, improper gap, and burned
electrodes, etc.)
Fuel system out of order.
• Variable fuel pressure
– Clogged fuel filter
– Kinky or damaged fuel hose and
line
– Faulty fuel pressure regulator
Engine and emission control system
out of order.
• Faulty EGR system
• Faulty MAF sensor
• Faulty injector
• Faulty ECM (PCM)
Engine overheating
Ignition system out of order.
• Faulty spark plug
• Improper ignition timing
Fuel system out of order.
• Clogged fuel filter and fuel lines
Engine and emission control system
out of order.
• Faulty EGR system
• Faulty ECT sensor or MAF sensor
• Faulty injector
• Faulty ECM (PCM)
Others
• Excessive combustion chamber
deposits
Correction
"Spark Plugs" in Section 6F1 or 6F2.
"Diag. Flow Table B-3" in this section.
"DTC P0400 Diag. Flow Table" in this sec-
tion.
"MAF Sensor" in Section 6E1.
"Fuel Injector" in Section 6E1.
"Inspection of ECM (PCM) and Its Circuit" in
this section.
Refer to "Overheating" in this table.
"Spark Plugs" in Section 6F1 or 6F2.
"Ignition Timing Check and Adjustment" in
Section 6F1 or 6F2.
"Fuel Pressure Check" in Section 6E1.
"DTC P0400 Diag. Flow Table" in this sec-
tion.
"ECT Sensor" or "MAF Sensor" in Section
6E1.
"Fuel Injector" in Section 6E1.
"Inspection of ECM (PCM) and Its Circuit" in
this section.
"Valves and Cylinder Head" and "Pistons,
Piston Rings, Connecting Rods and Cylin-
ders" in Section 6A1 or 6A4.