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<TD align=middle width="50%">Document ID# 839436
2003 HUMMER
H2
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<H1>Backfire</H1>
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Inspections</P></TH>
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Actions</P></TH></TR>
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DEFINITION: Fuel ignites in the intake manifold or in the exhaust
system, making a loud popping noise.</P></TD></TR>
<TR>
<TD vAlign=top align=left>
Preliminary Inspections</P></TD>
<TD vAlign=top align=left>
<UL type=BULLET>
<LI>Refer to Important Preliminary Inspections Before Starting in <A
href="http://127.0.0.1:9001/servlets/CellHandler?CellId=30562&RefDoc=839436">Symptoms
- Engine Controls</A> .
<LI>Search for bulletins.
<LI>Verify that the powertrain control module (PCM) grounds are clean,
tight, and in the proper locations. Refer to <A
href="http://127.0.0.1:9001/servlets/CellHandler?CellId=62050&RefDoc=839436">Power
and Grounding Component Views</A> in Wiring Systems and <A
href="http://127.0.0.1:9001/servlets/CellHandler?CellId=30158&RefDoc=839436">Engine
Controls Schematics</A> . </LI>[/list]</TD></TR>
<TR>
<TD vAlign=top align=left>
Fuel System</P></TD>
<TD vAlign=top align=left>
<UL type=BULLET>
<LI>Inspect for incorrect fuel pressure. Refer to <A
href="http://127.0.0.1:9001/servlets/CellHandler?CellId=30144&RefDoc=839436">Fuel
System Diagnosis</A> .
<LI>Inspect for a contaminated fuel condition. Refer to <A
href="http://127.0.0.1:9001/servlets/CellHandler?CellId=30353&RefDoc=839436">Alcohol/Contaminants-in-Fuel
Diagnosis</A> .
<LI>Inspect the fuel injectors. Refer to <A
href="http://127.0.0.1:9001/servlets/CellHandler?CellId=30125&RefDoc=839436">Fuel
Injector Coil Test</A> , <A
href="http://127.0.0.1:9001/servlets/CellHandler?CellId=30403&RefDoc=839436">Fuel
Injector Balance Test with Special Tool</A> or <A
href="http://127.0.0.1:9001/servlets/CellHandler?CellId=30404&RefDoc=839436">Fuel
Injector Balance Test with Tech 2</A> .
<LI>Verify that each injector harness is connected to the correct
injector or cylinder. Relocate injector harnesses as necessary.
</LI>[/list]</TD></TR>
<TR>
<TD vAlign=top align=left>
Sensor/System</P></TD>
<TD vAlign=top align=left>
<UL type=BULLET>
<LI>Inspect the air intake system and crankcase for air leaks.
<LI>Inspect the crankcase ventilation valve for proper operation. Refer
to <A
href="http://127.0.0.1:9001/servlets/CellHandler?CellId=65607&RefDoc=839436">Crankcase
Ventilation System Inspection/Diagnosis</A> in Engine Mechanical.
<LI>Inspect for an inaccurate speedometer. Refer to <A
href="http://127.0.0.1:9001/servlets/CellHandler?CellId=51427&RefDoc=839436">Symptoms
- Instrument Panel, Gages and Console</A> in Instrument Panel, Gages,
and Console.
<LI>Use a scan tool in order to monitor the knock sensor (KS) system for
excessive spark retard activity. Refer to <A
href="http://127.0.0.1:9001/servlets/CellHandler?CellId=30557&RefDoc=839436">Knock
Sensor (KS) System Description</A> . </LI>[/list]</TD></TR>
<TR>
<TD vAlign=top align=left>
Ignition System</P></TD>
<TD vAlign=top align=left>
<UL type=BULLET>
<LI>Inspect for proper ignition voltage output with J 26792 (http://127.0.0.1:9001/servlets/RetrieveTif?pic=5381)
Spark Tester .
<LI>Remove spark plugs and inspect for the following:
<UL type=SQUARE>
<LI>Wet plugs
<LI>Cracks
<LI>Wear
<LI>Improper gap
<LI>Burned electrodes
<LI>Heavy deposits </LI>[/list]</LI>[/list]
Refer to <A
href="http://127.0.0.1:9001/servlets/CellHandler?CellId=30554&RefDoc=839436">Spark
Plug Inspection</A> .</P>
<UL type=BULLET>
<LI>An improper spark plug gap will cause a driveability problem. Refer
to <A
href="http://127.0.0.1:9001/servlets/CellHandler?CellId=30554&RefDoc=839436">Spark
Plug Inspection</A> . Gap the spark plugs using a wire gage gap tool .
Refer to <A
href="http://127.0.0.1:9001/servlets/CellHandler?CellId=30325&RefDoc=839436">Spark
Plug Replacement</A> .
<LI>Determine the cause of the fouling before replacing the spark plugs.
Refer to <A
href="http://127.0.0.1:9001/servlets/CellHandler?CellId=30554&RefDoc=839436">Spark
Plug Inspection</A> for diagnosis.
<LI>Visually and physically inspect secondary ignition for the
following:
<UL type=SQUARE>
<LI>Ignition wires arcing to ground
<LI>Ignition coils arcing to ground </LI>[/list]
<LI>Soak the secondary ignition system with water from a spray bottle.
Soaking the secondary ignition system may help locate damaged or
deteriorated components. Look and listen for arcing or misfiring as you
apply the water.
<LI>Monitor the Misfire Current Counters while driving the vehicle in
the conditions that the misfire occurred. If a misfiring cylinder can be
located, use the DTCP0300 table for diagnosis. Refer to <A
href="http://127.0.0.1:9001/servlets/CellHandler?CellId=30479&RefDoc=839436">DTC
P0300</A>
<LI>Inspect for loose ignition coil grounds. Refer to <A
href="http://127.0.0.1:9001/servlets/CellHandler?CellId=30190&RefDoc=839436">Electronic
Ignition (EI) System Diagnosis</A> . </LI>[/list]</TD></TR>
<TR>
<TD vAlign=top align=left>
Engine Cooling System</P></TD>
<TD vAlign=top align=left>
<UL type=BULLET>
<LI>Inspect the engine coolant level for being low. Refer to <A
href="http://127.0.0.1:9001/servlets/CellHandler?CellId=37222&RefDoc=839436">Loss
of Coolant</A> in Engine Cooling.
<LI>Inspect the engine thermostat for proper operation and for the
correct heat range. Refer to <A
href="http://127.0.0.1:9001/servlets/CellHandler?CellId=37167&RefDoc=839436">Thermostat
Diagnosis</A> in Engine Cooling. </LI>[/list]</TD></TR>
<TR>
<TD vAlign=top align=left>
Engine Mechanical</P></TD>
<TD vAlign=top align=left>
<UL type=BULLET>
<LI>Inspect engine mechanical for the following:
<UL type=SQUARE>
<LI>Compression--Refer to <A
href="http://127.0.0.1:9001/servlets/CellHandler?CellId=43985&RefDoc=839436">Engine
Compression Test</A> in Engine Mechanical.
<LI>Sticking or leaking valves
<LI>Worn camshaft lobes
<LI>Valve timing
<LI>Bent push rods
<LI>Worn rocker arms
<LI>Broken valve springs
<LI>Excessive oil in combustion chamber or leaking valve seals--Refer
to <A
href="http://127.0.0.1:9001/servlets/CellHandler?CellId=44067&RefDoc=839436">Oil
Consumption Diagnosis</A> in Engine Mechanical. </LI>[/list]
<LI>For incorrect basic engine parts. Inspect the following:
<UL type=SQUARE>
<LI>The camshaft--Refer to <A
href="http://127.0.0.1:9001/servlets/CellHandler?CellId=44059&RefDoc=839436">Camshaft
and Bearings Cleaning and Inspection</A> in Engine Mechanical.
<LI>The cylinder heads--Refer to <A
href="http://127.0.0.1:9001/servlets/CellHandler?CellId=44030&RefDoc=839436">Cylinder
Head Cleaning and Inspection</A> in Engine Mechanical.
<LI>The pistons, etc.--Refer to <A
href="http://127.0.0.1:9001/servlets/CellHandler?CellId=44085&RefDoc=839436">Piston,
Connecting Rod, and Bearings Cleaning and Inspection</A> in Engine
Mechanical. </LI>[/list]
<LI>Refer to <A
href="http://127.0.0.1:9001/servlets/CellHandler?CellId=44155&RefDoc=839436">Symptoms
- Engine Mechanical</A> in Engine Mechanical for diagnosis procedures.
</LI>[/list]</TD></TR>
<TR>
<TD vAlign=top align=left>
Additional Inspections</P></TD>
<TD vAlign=top align=left>
<UL type=BULLET>
<LI>Visually and physically inspect the vacuum hoses for splits, kinks,
and proper connections and routing as shown on the Vehicle Emission
Control Information label.
<LI>Inspect the intake manifold and the exhaust manifold passages for
casting flash.
<LI>Inspect the transmission torque converter clutch (TCC) operation.
The scan tool should indicate an RPM drop when the TCC is commanded ON.
Refer to <A
href="http://127.0.0.1:9001/servlets/CellHandler?CellId=75303&RefDoc=839436">Diagnostic
System Check - Automatic Transmission</A> in Automatic
Transmission-4L60-E.
<LI>Inspect the exhaust system for possible restrictions. Inspect the
following:
<UL type=SQUARE>
<LI>Inspect the exhaust system for damaged or collapsed pipes.
<LI>Inspect the mufflers for heat distress or possible internal
failure.
<LI>Inspect for possible plugged catalytic converters. Refer to <A
href="http://127.0.0.1:9001/servlets/CellHandler?CellId=62242&RefDoc=839436">Restricted
Exhaust</A> in Engine Exhaust. </LI>[/list]</LI>[/list]
<UL type=BULLET>
<LI>Electromagnetic interference (EMI) on the reference circuit can
cause an engine miss condition. A scan tool can usually detect EMI by
monitoring the engine RPM. A sudden increase in RPM with little change
in actual engine RPM change may indicate that EMI is present. If a
problem exists, inspect for high voltage components near the ignition
control circuits.
<LI>Inspect the park/neutral position (PNP) switch operation. Refer to
<A
href="http://127.0.0.1:9001/servlets/CellHandler?CellId=6964&RefDoc=839436">Park/Neutral
Position Switch Adjustment</A> in Automatic Transmission-4L60-E.
<LI>Inspect for faulty motor mounts. Refer to <A
href="http://127.0.0.1:9001/servlets/CellHandler?CellId=44042&RefDoc=839436">Engine
Mount Inspection</A> in Engine Mechanical.
<LI>Inspect the intake manifold and the exhaust manifold passages for
casting flash </LI>[/list]</TD></TR></TBODY></TABLE>
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<TD align=middle width="50%">Document ID# 839436
2003 HUMMER
H2
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