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