permission granted to reproduce for educational use only. 1 © goodheart-willcox co., inc

Permission granted to reproduce for educational use only.1© Goodheart-Willcox Co., Inc.


Engine Problem Diagnosis and Tune-Up

Chapter 19


Objectives

Describe a minor tune-up and a major tune-up.

List tune-up safety rules.

List items to look for in a preliminary inspection.

Perform a current starter draw test.


Objectives

Perform dry and wet compression tests and analyze the results.

Perform a cylinder leakage test and analyze the results.

Perform a vacuum test and analyze the results.


Objectives

Perform a cylinder balance test and analyze the results.

Describe valve adjustment.

List general tune-up rules.


What Is a Tune-Up?

Engine tune-up returns engine to peak performance after part wear and deterioration

Tune-up involvesReplacing worn parts

Performing basic service tasks

Making adjustments


Minor Tune-Up

Minor tune-up is preventative maintenancePerformed when engine is in good condition

Engine has little or no wear


Minor Tune-Up (Cont.)

Visually inspect for problems

Listen for abnormal noises

Check condition of engine oil and coolant



Check for trouble codes in computer

Replace distributor cap, rotor, and spark plugs (older, high-mileage vehicles)

Check and adjust ignition timing

Replace air and fuel filters

Make fuel system adjustments where applicable



Clean throttle body, idle air bypass, and EGR system

Test and service emission control system

Fill all fluid reservoirs to correct level

Road test the vehicle


Major Tune-Up

Major tune-up is done when systems or engine is in poor condition and includes

All parts of minor tune-up

Diagnostic tests to determine what should be done to bring vehicle back to good operating condition


Tune-Up Safety

Engage emergency brake and block wheels when engine is to be running

Place exhaust hose over tailpipe when running engine in enclosed shop

Keep clothing, hands, tools, and equipment away from moving parts

Disconnect battery when recommended

Be careful not to touch hot exhaust manifold


Tune-Up Safety (Cont.)

Keep test equipment leads away from exhaust manifolds, fan, and beltsWear eye protection when blowing debris from parts or when working near engine fanKeep fire extinguisher handy, especially during fuel system tests and repairsWith diesel engine, disable injection pump when removing injection line


Preliminary Inspection

Look for problems withBattery

Air cleaner

Fuel system

Belts and hoses

Poor electrical connections

Fix problems before proceeding with tune-up


Evaluating the Engine and Its Systems

If scan tool indicates problem with oxygen sensor, remove and inspect sensor

Note color of tip of oxygen sensorColor can indicate condition of engine and support systems


Evaluating the Engine and Its Systems (Cont.)

(Tomco, Inc.)


Evaluating the Engine and Its Systems (Cont.)

If engine is running too hot or cold, measure operating temperature

Use engine analyzer or handheld tester to check for blown head gasket

To find hard-to-locate oil and coolant leaks, add dye and use a black light


Cranking Balance Test

Cranking balance test finds cylinders with low compression

Monitors current drawn by starter motor during complete turn of crankshaft

Low current draw indicates that starter is not being loaded enough by compression stroke


Compression Test

Compression test determines engine’s mechanical conditionLow compression may be caused by

Burned valve or valve seatPhysical engine damageBlown head gasketWorn rings or cylindersValve train troublesJumped timing chain or belt


Compression Test—Gasoline Engine

Remove all spark plugsBlock open throttle platesDisable ignition systemDisable fuel injection systemScrew compression gauge into spark plug holeCrank engine and let it rotate for about six compression strokes


Compression Test—Gasoline Engine (Cont.)

Write down readings for each cylinder

Compare readings to specifications

(Snap-on Tool Corp.)


Compression Test—Diesel Engine

Procedure is similar to compression test for gasoline engine

Do not use compression gauge intended for gasoline engine on diesel engine

Diesel compression gauge must read up to 600 psi (4200 kPa)


Compression Test Results

Gasoline engine readings should be 125-175 psi (860-1200 kPa) in each cylinder

Diesel engine readings should be 275-400 psi (1900-2750 kPa)


Compression Test Results (Cont.)

Look for cylinder pressure variations during compression check


Wet Compression Test

Wet compression test should be done on any cylinder with compression reading below specifications


Wet Compression Test (Cont.)


Cylinder Leakage Test

Cylinder leakage test measures air leakage out of engine combustion chamber


Vacuum Test

Vacuum test measures intake manifold vacuum

(General Motors)


Cylinder Balance Test

Cylinder balance test disables spark plug in one cylinder at a time

Tests whether cylinders are firing properly


Valve Adjustment

On some engines, valve adjustment involves turning rocker arm adjusting screws

(Volvo)


Valve Adjustment (Cont.)

On some OHC engines, valve adjustment involves changing shim thickness to alter valve lash

(Ford)


Tune-Up Parts Replacement

Depending on age and condition of engine, parts may need replacement during tune-up

On newer vehicles, only spark plugs and filters may need replacement

Older vehicles with high mileage may need multiple parts


Tune-Up Parts Replacement (Cont.)

Parts that may need replacing includeSpark plugs

Spark plug wires

Distributor parts

Fuel system parts

Emission control parts


Tune-Up Adjustments

Adjustments needed will vary with make, model, and condition of vehicle

Most common adjustments includeSpark plug gap

Pickup coil air gap

Ignition timing or injection timing

Idle speed


Tune-Up Adjustments (Cont.)

(Snap-on Tool Corp.)


General Tune-Up Rules

Gather information about performance of engine

Use professional, high-quality tools and equipment

Make sure engine has warmed to full operating temperature

Refer to service information or emission sticker for specifications and procedures


General Tune-Up Rules (Cont.)

Use quality parts

Keep service records

Complete basic maintenance service

Inform customer about tune-up intervals

Road test the vehicle when tune-up is complete


Diesel Engine Tune-Up(Maintenance)

Diesel maintenance involvesReplacing air filter element

Cleaning, draining, or replacing fuel filters

Adjusting engine idle speed and throttle cable

Inspecting engine and related systems

Checking injection timing

Changing engine oil and oil filter

Servicing emission control systems periodically


Review Questions

A major tune-up consists of a minor tune-up plus which of the following?

A. Oil change

B. Coolant change

C. Battery recharge

D. Diagnostic tests

Answer: D. Diagnostic tests


Review Questions

When working on a diesel engine, disable the ____.

Answer: injection pump


Review Questions

True or False? Checking for fuel system leaks is part of the preliminary inspection.

Answer: True


Review Questions

A cranking balance test will locate cylinders with ____ compression.

Answer: low


Review Questions

True or False? A wet compression test is used to locate defective valves.

Answer: False. A wet compression test is used to locate defective rings.


Review Questions

In a(n) ____ test, shop air is pumped into a cylinder and a pressure gauge is used to measure air leakage.

Answer: cylinder leakage


Review Questions

What would cause a vacuum gauge to show higher than normal readings while idling in neutral?

A. Burned exhaust valveB. Burned intake valveC. Worn oil ringsD. None of the above.Answer: D. None of the above.


Review Questions

What test is commonly performed to find out if individual cylinders are firing properly?

Answer: Cylinder balance test


Review Questions

In some ____ engines, valves must be adjusted by changing the shim thickness.

Answer: OHC


Review Questions

True or False? Diesel engines should be tuned up at regular intervals, just like gasoline engines.

Answer: False. Diesel engines do not require periodic tune-ups.

permission granted to reproduce for educational use only. 1 © goodheart-willcox co., inc

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