Hummer H2. Manual — part 31

Hesitation

Cracked or broken vacuum

Replace vacuum hoses hoses

Vacuum leaks

Repair Vacuum leaks

Binding carburetor linkage

Eliminate binding

Binding throttle linkage

Eliminate binding

Binding choke linkage or fast idle
cam

Eliminate binding

Improper float setting

Readjust float setting, see FUEL

Cracked or broken ignition wires

Replace ignition wires

Rough Idle, Missing or Stalling

Incorrect curb idle or fast idle
speed

Reset idle speed, see see ENGINE

PERFORMANCE

Incorrect basic timing

Reset ignition timing see ENGINE

PERFORMANCE

Improper idle mixture adjustment

Reset idle mixture, see ENGINE

PERFORMANCE

Improper feedback system
operation

Check feedback system see ENGINE

PERFORMANCE

Incorrect spark plug gap

Reset spark plug gap, see ENGINE

PERFORMANCE

Moisture in ignition components

Dry components

Loose or broken ignition wires

Replace ignition wires

Damaged distributor cap or or rotor

Replace distributor cap or rotor

Faulty ignition coil

Replace ignition coil

Fuel filter clogged or worn

Replace fuel filter

Damaged idle mixture screw

Replace idle mixture screw, see FUEL

Improper fast idle cam adjustment

Reset fast idle cam adjustment, see TUNE- see

ENGINE PERFORMANCE

Improper EGR valve operation

Replace EGR valve

Faulty PCV valve air flow

Replace PCV valve

Choke binding or improper choke
setting

Reset choke or eliminate binding

Vacuum leak

Repair vacuum leak

Improper float bowl fuel level

Reset float adjustment, see FUEL

Clogged air bleed or idle passages

Clean carburetor passages, see FUEL

Clogged or worn air cleaner filter

Replace air filter

Faulty choke vacuum diaphragm

Replace diaphragm, see ENGINE

PERFORMANCE

Exhaust manifold heat valve
inoperative

Replace heat valve

Improper distributor spark advance

Check distributor operation

1998 Chevrolet Pickup C1500

GENERAL INFORMATION Trouble Shooting - Basic Procedures

Leaking valves or valve
components

Check and repair valvetrain

Improper carburetor mounting

Remove and remount carburetor

Excessive play in distributor shaft

Replace distributor

Loose or corroded wiring
connections

Repair or replace as required

Engine Surges

Improper PCV valve airflow

Replace PCV valve

Vacuum leaks

Repair vacuum leaks

Clogged air bleeds

Remove restriction

EGR valve malfunction

Replace EGR valve

Restricted air cleaner filter

Replace air filter

Cracked or broken vacuum hoses

Replace vacuum hoses

Cracked or broken ignition wires

Replace ignition wires

Vacuum advance malfunction

Check unit and replace as necessary

Defective or fouled spark plugs

Replace spark plugs

Ping or Spark Knock

Incorrect ignition timing

Reset ignition timing see ENGINE

PERFORMANCE

Distributor centrifugal or vacuum
advance malfunction

Check operation and replace as necessary

Carburetor setting too lean

Readjust mixture setting, see ENGINE

PERFORMANCE

Vacuum leak

Eliminate vacuum leak

EGR valve malfunction

Replace EGR valve

Poor Gasoline Mileage

Cracked or broken vacuum

Replace vacuum hoses hoses

Vacuum leaks

Repair vacuum leaks

Defective ignition wires

Replace wires

Incorrect choke setting

Readjust setting, see ENGINE PERFORMANCE

Defective vacuum advance

Replace vacuum advance

Defective spark plugs

Replace spark plugs

Binding carburetor power piston

Eliminate binding

Dirt in carburetor jets

Clean and/or replace jets

Incorrect float adjustment

Readjust float setting, see FUEL

Defective power valve

Replace power valve, see ENGINE

PERFORMANCE

Incorrect idle speed

Readjust idle speed

Engine Stalls

Improper float level

Readjust float level

1998 Chevrolet Pickup C1500

GENERAL INFORMATION Trouble Shooting - Basic Procedures

VACUUM PUMP - DIESEL TROUBLE SHOOTING

VACUUM PUMP (DIESEL) TROUBLE SHOOTING CHART

MANUAL TRANSMISSION

MANUAL TRANSMISSION TROUBLE SHOOTING

MANUAL TRANSMISSION/TRANSAXLE TROUBLE SHOOTING

Leaking needle valve and seat

Replace needle valve and seat

Vacuum leaks

Eliminate vacuum leaks

NOTE:

This is GENERAL information. This article is not intended to be specific to any
unique situation or individual vehicle configuration. The purpose of this Trouble
Shooting information is to provide a list of common causes to problem
symptoms. For model-specific Trouble Shooting, refer to SUBJECT,
DIAGNOSTIC, or TESTING articles available in the section(s) you are accessing.

NOTE:

Diesel engines mechanical diagnosis is the same as gasoline engines for items
such as noisy valves, bearings, pistons, etc. The following trouble shooting
covers only items pertaining to diesel engines.

CONDITION & POSSIBLE CAUSE

CORRECTION

Excessive Noise

Loose pump-to-drive assembly screws

Tighten screws

Loose tube on pump assembly

Tighten tube

Valves not functioning properly

Replace valves

Oil Leakage

Loose end plug

Tighten end plug

Bad seal crimp

Remove and re-crimp seal

NOTE:

This is GENERAL information. This article is not intended to be specific to any
unique situation or individual vehicle configuration. The purpose of this Trouble
Shooting information is to provide a list of common causes to problem
symptoms. For model-specific Trouble Shooting, refer to SUBJECT,
DIAGNOSTIC, or TESTING articles available in the section(s) you are accessing.

Condition

Possible Cause

Noisy In Forward Gears

Low gear oil level, Loose bell housing bolts, Worn bearings

or gears

Clunk On Deceleration
(FWD Only)

Loose engine mounts, Worn inboard CV joints, Worn

differential pinion shaft, Side gear hub counterbore in case

worn oversize

1998 Chevrolet Pickup C1500

GENERAL INFORMATION Trouble Shooting - Basic Procedures

POWERTRAIN

CLUTCH TROUBLE SHOOTING

Gear Clash When Shifting
Forward Gears

Clutch Out Of Adjustment, Shift linkage damaged or out of

adjustment, Gears or synchronizers damaged, Low gear oil

level

Transmission Noisy When
Moving (RWD Only)
Quiet In Neutral With
Clutch Engaged

Worn rear outputshaft bearing

Gear Rattle

Worn bearings, Wrong gear oil, Low gear oil, Worn gears

Steady Ticking At Idle
(Increases With RPM)

Broken tooth on gear

Gear Clash When Shifting
Forward Gears

Worn or broken synchronizers

Loud Whine In Reverse

Normal condition

(1)

Noise When Stepping On
Clutch

Bad release bearing, Worn pilot bearing

Ticking Or Screeching As
Clutch Is Engaged

Faulty release bearing, Uneven pressure plate fingers

Click Or Snap When
Clutch Is Engaged

Worn clutch fork, Worn or broken front bearing retainer

Transmission Shifts Hard

Clutch not releasing, Shift mechanism binding, Clutch

installed backwards

Will Not Shift Into One
Gear, Shifts Into All
Others

Bent shift fork, Worn detent balls

Locked Into Gear, Cannot
Shift

Clutch adjustment, Worn detent balls

Transmission Jumps Out
Of Gear

Pilot bearing worn, Bent shift fork, Worn gear teeth or face,

Excessive gear train end play, Worn synchronizers, Missing

detent ball spring, Shift mechanism worn or out of

adjustment, Engine or transmission mount bolts loose or out

of adjustment, Transmission not aligned

Shift Lever Rattle

Worn shift lever or detents, Worn shift forks, Worn

synchronizers sleeve

Shift Lever Hops Under
Acceleration

Worn engine or transmission mounts

(1)

Most units use spur cut gears in reverse and are noisy

NOTE:

This is GENERAL information. This article is not intended to be specific to any

1998 Chevrolet Pickup C1500

GENERAL INFORMATION Trouble Shooting - Basic Procedures