Hummer H2. Instruction - page 71

Poor Acceleration

Incorrect Ignition Timing

Reset Timing

Leaky Valves

Check Compression

Component Failure

Spark Arcing

Replace Faulty Part

Defective Pick-Up Coil

Replace Pick-Up Coil

Defective Ignition Coil

Replace Ignition Coil

Defective Control Unit

Replace Control Unit

Ignition Diagnosis By Scope Pattern

All Firing Lines Abnormally High

Retarded Ignition Timing

Reset Ignition Timing

Lean Air/Fuel Mixture

Adjust Fuel Mixture

High Secondary Resistance

Repair Secondary Ignition

All Firing Lines Abnormally Low

Rich Air/Fuel Mixture

Adjust Air/Fuel Mixture

Arcing Coil Wire

Replace Coil Wire

Cracked Coil

Replace Coil

Low Coil Output

Replace Coil

Low Compression

Check/Repair Engine

Several High Firing Lines

Fuel Mixture Unbalanced

Check Fuel System

EGR Valve Stuck Open

Clean/Replace EGR Valve

High Plug Wire Resistance

Replace Plug Wire

Cracked/Broken Plugs

Replace Plugs

Intake Vacuum Leak

Repair Leak

Several Low Firing Lines

Fuel Mixture Unbalanced

Adjust Fuel Mixture

Plug Wires Arcing

Replace Plug Wires

Cracked Coil Arcing

Replace Coil

Uneven Compression

Check/Repair Engine

Faulty Spark Plugs

Replace Plugs

Cylinders Not Firing

Cracked Distributor Cap

Replace Cap

Shorted Plug Wires

Replace Plug Wires

Mechanical Engine Fault

Check/Repair Engine

Spark Plugs Fouled

Replace Plugs

Carbon Track in Distributor Cap

Replace Cap

Hard Starting

Defective Ignition Coil(s)

Replace Coil(s)

1998 Chevrolet Pickup C1500

GENERAL INFORMATION TROUBLE SHOOTING

FUEL INJECTION TROUBLE SHOOTING

Fouled Spark Plugs

Replace Plugs

Incorrect Timing

Reset Ignition Timing

Problem & Possible Cause

Action

Cold Start Valve Inoperative

Test Cold Start Valve

Poor Vacuum/Electrical Connection

Repair Connections

Contaminated Fuel

Test Fuel for Water/Alcohol

Bad Fuel Pump Relay/Circuit

Test Relay/Wiring

Battery Voltage Low

Charge/Test Battery

Low Fuel Pressure

Test Press. Regulator/Pump

No Distributor Reference Pulse

Repair Ignition System

Coolant Temp. Sensor Defective

Test Temp. Sensor/Circuit

No Power To Injectors

Check Injector Fuse/Relay

Hard Starting

Defective Idle Air Control (IAC)

Test IAC and Circuit

EGR Valve Open

Test EGR Valve/Control Circuit

Restricted Fuel Lines

Inspect/Replace Fuel Lines

Poor MAP Sensor Signal

Test MAP Sensor/Circuit

Engine Stalls During Parking Maneuver

Check P.S. Press. Switch

Rough Idle

Dirty Fuel Injectors

Clean/Replace Injectors

Poor MAP Sensor Signal

Test MAP Sensor/Circuit

Intermittent Fuel Injector Operation

Check Harness Connectors

Erratic Vehicle Speed Sensor Inputs

Harness Too Close to Plug Wires

Poor O

2

Sensor Signal

Test O

2

Sensor/Circuit

Faulty PCV System

Check PCV Valve and Hoses

Poor Acceleration

Weak Fuel Pump

Replace Fuel Pump

Dirty Fuel Injectors

Clean/Replace Injectors

Excessive Intake Valve Deposits

Clean Intake System

Poor High Speed Operation

Low Fuel Pump Volume

Faulty Fuel Pump/Filter

Poor MAP Sensor Signal

Test Speed Sensor/Circuit

Acceleration Ping/Knock

Faulty EGR System

Check EGR Valve and Hoses

Poor Knock Sensor Signal

Test Knock Sensor/Circuit

Poor Baro Sensor Signal

Test Baro Sensor/Circuit

Improper Ignition Timing

Adjust Timing

1998 Chevrolet Pickup C1500

GENERAL INFORMATION TROUBLE SHOOTING

Engine Overheating

Check Cooling System

Poor Quality Fuel

Use Different Fuel

Carbon Build-Up

Decarbon Engine

1998 Chevrolet Pickup C1500

GENERAL INFORMATION TROUBLE SHOOTING

GENERAL INFORMATION

Gear Tooth Contact Patterns

INSPECTION

Wipe lubricant from internal parts. Rotate gears and inspect for wear or damage. Mount dial indicator to
housing and check backlash at several points around ring gear. Backlash must be within specification at all
points. If no defects are found, check gear tooth pattern contact.

GEAR TOOTH CONTACT PATTERN

1. Paint ring gear teeth with marking compound. Wrap cloth or rope around drive pinion flange to act as

brake. Rotate gear until clear contact pattern is obtained.

2. Contact pattern will indicate whether correct pinion bearing mounting shim has been installed and if drive

gear backlash has been set properly. Backlash between drive gear pinion must be maintained within
specified limits until correct tooth pattern is obtained.

ADJUSTMENTS

GEAR BACKLASH & PINION SHIM CHANGES

1. With no change in backlash, moving pinion further from ring gear moves drive pattern toward heel and

top of tooth, and moves coast pattern toward toe and top of tooth.

2. With no change in backlash, moving pinion closer to ring gear moves drive pattern toward toe and bottom

of tooth, and moves coast pattern toward heel and bottom of tooth.

3. With no change in pinion shim thickness, an increase in backlash moves ring gear further from pinion.

Both drive and coast patterns move toward heel and top of tooth.

4. With no change in pinion shim thickness, a decrease in backlash moves ring gear closer to pinion gear.

Both drive and coast patterns move toward toe and bottom of tooth.

NOTE:

Drive pattern should be well centered on ring gear teeth. Coast pattern should
be centered, but may be slightly toward toe of ring gear teeth.

1998 Chevrolet Pickup C1500

GENERAL INFORMATION Gear Tooth Contact Patterns

1998 Chevrolet Pickup C1500

GENERAL INFORMATION Gear Tooth Contact Patterns

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