Hummer H2. Manual — part 30

BASIC ELECTRONIC IGNITION TROUBLE SHOOTING CHARTS

BASIC ELECTRONIC IGNITION TROUBLE SHOOTING CHARTS - USING OSCILLOSCOPE
PATTERNS

combustion

Improper gapping procedure

Re-gap spark plugs

Rust Colored Deposits

Additives in unleaded fuel

Try different fuel brand

Water In Combustion Chamber

Blown head gasket or cracked head

Repair or replace head or head gasket

NOTE:

Before diagnosing an electronic ignition system, ensure that all wiring is
connected properly between distributor, wiring connector and spark plugs.
Ignition problem will show up either as: Engine Will Not Start or Engine Runs
Rough.

CONDITION & POSSIBLE CAUSE

CORRECTION

Engine Won't Start

Open circuit between distributor and
bulkhead connector

Repair circuit

Open circuit between bulkhead connector
and ignition switch

Repair circuit

Open circuit between ignition switch and
starter solenoid

Repair circuit

Engine Runs Rough

Fuel lines leaking or clogged

Tighten fitting, remove restriction

Initial timing incorrect

Reset ignition timing see ENGINE

PERFORMANCE

Centrifugal advance malfunction

Repair distributor advance

Defective spark plugs or wiring

Replace plugs or plug wiring

Component Failure

Spark arc-over on cap, rotor or coil

Replace cap, rotor or or coil

Defective pick-up coil

Replace pick-up coil

Defective ignition coil

Replace ignition coil

Defective vacuum unit

Replace vacuum unit

Defective control module

Replace control module

CONDITION & POSSIBLE
CAUSE

CORRECTION

Firing Voltage Lines are the Same, but Abnormally High

Retarded ignition timing

Reset ignition timing, see ENGINE

PERFORMANCE section

1998 Chevrolet Pickup C1500

GENERAL INFORMATION Trouble Shooting - Basic Procedures

Fuel mixture too lean

Readjust carburetor, see ENGINE

PERFORMANCE

High resistance in coil wire

Replace coil wire

Corrosion in coil tower terminal

Clean and/or replace coil

Corrosion in distributor coil
terminal

Clean and/or replace distributor cap

Firing Voltage Lines are the Same but Abnormally Low

Fuel mixture too rich

Readjust carburetor, see ENGINE

PERFORMANCE

Breaks in coil wire causing
arcing

Replace coil wire

Cracked coil tower causing
arcing

Replace coil

Low coil output

Replace coil

Low engine compression

Determine cause and repair

One or More, But Not All Firing Voltage Lines are Higher Than Others

Carburetor idle mixture not
balanced

Readjust carburetor, see ENGINE

PERFORMANCE

EGR valve stuck open

Clean and/or replace valve

High resistance in spark plug
wires

Replace spark plug wires

Cracked or broken spark plug
insulator

Replace spark plugs

Intake vacuum leak

Repair leak

Defective spark plugs

Replace spark plugs

Corroded spark plug terminals

Replace spark plugs

One or More, But Not All Firing Voltage Lines Are Lower Than Others

Curb idle mixture not balanced

Readjust carburetor, see ENGINE

PERFORMANCE

Breaks in plug wires

Replace plug wires causing arcing

Cracked coil tower causing
arcing

Replace coil

Low compression

Determine cause and repair

Defective spark plugs

Replace spark plugs

Corroded spark plugs

Replace spark plugs

Cylinders Not Firing

Cracked distributor cap
terminals

Replace distributor cap

Shorted spark plug wire

Determine cause and repair

Mechanical problem in engine

Determine cause and repair

Defective spark plugs

Replace spark plugs

1998 Chevrolet Pickup C1500

GENERAL INFORMATION Trouble Shooting - Basic Procedures

BASIC DRIVEABILITY PROBLEMS TROUBLE SHOOTING

Spark plugs fouled

Replace spark plugs

CONDITION & POSSIBLE
CAUSE

CORRECTION

Hard Starting

Binding carburetor linkage

Eliminate binding

Binding choke linkage

Eliminate binding

Binding choke piston

Eliminate binding

Restricted choke vacuum

Check vacuum lines for blockage

Worn or dirty needle valve and seat Clean carburetor, see ENGINE PERFORMANCE

Float sticking

Readjust or replace float see the ENGINE

PERFORMANCE section

Incorrect choke adjustment

Reset choke adjustment see ENGINE

PERFORMANCE

Defective coil

Replace coil

Improper spark plug gap

Regap spark plugs

Incorrect ignition timing

Reset ignition timing see ENGINE

PERFORMANCE

Detonation

Over-advanced ignition timing

Reset ignition timing see ENGINE

PERFORMANCE

Defective spark plugs

Replace spark plugs

Fuel lines clogged

Clean fuel lines

EGR system malfunction

Check and repair EGR system

PCV system malfunction

Repair PCV system

Vacuum leaks

Check and repair vacuum system

Loose fan belts

Tighten or replace fan belts, see ENGINE

PERFORMANCE

Restricted airflow

Remove restriction

Vacuum advance malfunction

Check distributor operation

Dieseling

Binding carburetor linkage

Eliminate binding

Binding throttle linkage

Eliminate blinding

Binding choke linkage or fast idle
cam

Eliminate binding

Defective idle solenoid

Replace idle solenoid see ENGINE

PERFORMANCE

Improper base idle speed

Reset idle speed, see see ENGINE

PERFORMANCE

Incorrect ignition timing

Reset ignition timing see ENGINE

1998 Chevrolet Pickup C1500

GENERAL INFORMATION Trouble Shooting - Basic Procedures

PERFORMANCE

Incorrect idle mixture setting

Reset idle mixture, see ENGINE

PERFORMANCE

Faulty Acceleration

Incorrect ignition timing

Reset ignition timing see ENGINE

PERFORMANCE

Engine cold and choke too lean

Adjust choke and allow engine to warm-up

Defective spark plugs

Replace spark plugs

Defective coil

Replace coil

Faulty Low Speed Operation

Clogged idle transfer slots

Clean idle transfer slots, see FUEL

Restricted idle air bleeds and
passages

Disassemble and clean carburetor, see FUEL

Clogged air cleaner

Replace air filter

Defective spark plugs

Replace spark plugs

Defective ignition wires

Replace ignition wire see ENGINE

PERFORMANCE

Defective distributor cap

Replace distributor cap

Faulty High Speed Operation

Incorrect ignition timing

Reset ignition timing see ENGINE

PERFORMANCE

Defective distributor centrifugal
advance

Replace advance mechanism

Defective distributor vacuum
advance

Replace advance unit

Incorrect spark plugs or plug gap

Check gap and/or replace spark plugs

Faulty choke operation

Check choke and repair as required

Clogged vacuum passages

Remove restrictions

Improper size or clogged main jet

Check jet size and clean, see FUEL

Restricted air cleaner

Check filter and replace as necessary

Defective distributor cap, rotor or
coil

Replace cap, rotor or coil

Misfire at All Speeds

Defective spark plugs

Replace spark plugs

Defective spark plug wires

Replace spark plug wires

Defective distributor cap, rotor, or
coil

Replace cap, rotor, or coil

Cracked or broken vacuum hoses

Replace vacuum hoses

Vacuum leaks

Repair vacuum leaks

Fuel lines clogged

Remove restriction

1998 Chevrolet Pickup C1500

GENERAL INFORMATION Trouble Shooting - Basic Procedures