Hummer H2. Manual - part 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