chapter 48 engine problems

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

Publisher

The Goodheart-Willcox Co., Inc.Tinley Park, Illinois

by

Russell Krick


Why is diagnosis important? Symptoms of engine mechanical

problems Decide what type of engine repair is

needed Evaluating engine mechanical

problems Service manual troubleshooting charts


If a technician does not know how to properly diagnose engine problems, time, effort, and money will be wasted

An untrained technician may rebuild an engine when a minor repair would have corrected the fault


Excessive oil consumption Excessive crankcase blowby Noises Exhaust smoke Poor performance Coolant in the oil Engine seizure


Engine Mechanical Problems


Pre-Teardown Inspection

Run the engine Look for external problems:

oil leaks vacuum leaks part damage contaminated oil

Listen and watch for problems


Check Oil Condition Check for coolant in the oil

shows up as white or milky oil

Check for gasoline in the oil smell the dipstick for gasoline


Oil-Fouled Spark Plugs

Indicate internal oil leakage into the combustion chambers—caused by worn

rings, cylinder walls, or valve seals


Oil In Coolant

Causes: a leak in the radiator oil cooler head gasket leakage a cracked block or head


Engine Oil Leaks Causes:

gaskets harden and crack seals wear fasteners work loose parts become warped or cracked

To isolate leaks: clean the affected area trace the leak upward to its source


External Coolant Leaks

Causes: hose problems rusted freeze (core) plugs warped, worn, or damaged parts

Use a pressure tester to locate leaks


Engine Blowby


Engine Vacuum Leaks

May produce a hissing sound Affect idle quality more than high speed

conditions leaks represent a greater percentage of

engine airflow at idle than at high speed


Engine Exhaust Leaks

Produce a clicking sound Causes:

leaking exhaust gaskets a warped exhaust manifold loose manifold bolts


Engine Exhaust Leaks

The leakage path can be easily seen after exhaust manifold removal


Engine Smoking


Abnormal Engine Noises

Indicate part wear or damage Use a stethoscope to find internal

noises A piece of hose can be used

place one end next to your ear, use the other end to probe around the engine


Compression Test Measures the amount of pressure

produced during the compression stroke

Performed any time symptoms point to cylinder pressure leakage rough idle popping noise in intake or exhaust blue exhaust smoke excess blowby


Combustion Leakage


Compression Testing(Gasoline Engine)

Remove all spark plugs Block open the throttle Disable the ignition and fuel injection Screw the compression tester into a

spark plug hole Crank the engine through 4–6

compression strokes, noting the readings

Repeat for each cylinder


Compression Tester


Installing Adapter


Connect Compression Gauge


Cranking Engine


Replacing Plugs and Wires


Compression Testing(Diesel Engine)

Use a diesel compression gauge that reads up to approximately 600 psi(4000 kPa)

Remove the injectors or the glow plugs Install the tester in the recommended

hole Disable the injection pump Crank the engine, noting the readings Repeat for each cylinder


Wet Compression Test Performed if a cylinder fails a

compression test Helps isolate cylinder and ring

problems from valve problems Oil is squirted into the cylinder before

the compression test if the pressure rises, the rings and

cylinder are suspect if the pressure does not rise, the valves

are suspect


Wet Compression Test

A. Perform dry test B. Squirt oil into cylinder

C. Measure again


Compression Test Results

Refer to service manual for specifications

Typical gasoline engines 125–175 psi (860–1200 kPa)

Typical diesel engines 275–400 psi (1900–2750 kPa)

Maximum variation 10–15% between cylinders


Cylinder Leakage Tester

Measures the amount of air leakage out of a cylinder

Shop air pressure is forced into the cylinder on Top Dead Center

Pressure gauge reads percentage of leakage out of the cylinder

Typical maximum leakage is 20%


Cylinder Leakage Tester

If leakage exceeds specifications, listen at various points to isolate leakage

Oil filler cap—ring leakage Throttle body—intake valve leakage Exhaust pipe—exhaust valve leakage Radiator bubbles—head gasket or

cracked head, block


After performing inspections and tests, decide what part or parts must be repaired or replaced

Evaluate your pre-teardown diagnosis If you still can’t determine the problem,

partially disassemble the engine for further inspection


Valve Train Problems


Burned Valve

Causes an engine miss, a popping sound at the throttle body or exhaust


Worn Valve Guidesand Stems

Causes tapping noise, oil consumption, spark plug fouling, or stem

breakage


Leaking Valve Stem Seal

Lets oil drain through the clearance between the stem and guide

Oil will be pulled into the intake port and burned

Causes blue exhaust smoke, especially after startup


Valve Breakage

Caused by valve stem fatigue or by a broken or weak valve spring

Usually causes severe piston and cylinder damage


Stuck Valve

Valve stem rusts or corrodes and locks in the valve guide

May happen when the engine sits in storage


Valve Float

Excess engine speed, weakened valve springs, or lifter problems cause the valves to remain partially open

Usually occurs at higher engine speeds Engine may miss, pop, or backfire


Worn Timing Chain

Causes reduced compression and power


Worn Timing Belt

May break, jump off its sprockets, or skip a few teeth

Severe lack of power, no-start, and valve damage can result


Camshaft Problems

Worn cam lobes Worn journals Broken cams Worn distributor drive gear Loose or worn fuel pump drive

eccentric


Cam Lobe Wear

Reduces valve lift and power output


Rocker Arm and Push Rod Problems

May cause clatter (light tapping noise) Rocker arms may wear Push rods may be bent To check, roll the push rods on a flat

bench


Valve Train Clearance

Excess clearance can produce noise


Hydraulic Lifter Problems

Worn or defective hydraulic lifters may produce valve clatter

To check, remove the valve cover Try adjusting the valves If adjustment will not quiet the noise,

check for valve train wear If the valve train passes, the lifter is bad Low oil pressure can cause lifter noise


Piston Knock (Slap)

Loud, metallic knock that is loudest whenthe engine is cold


Piston Pin Knock

Too much clearance between the piston pin and the pin bore or connecting rod bushing

Makes a double knock The noise does not change much with

engine load


Worn Rings and Cylinder


Worn Ring Grooves


Burned Piston

Results from prolonged preignition or detonation

Causes low compression, blowby, smoking, and rough idle


Burned Piston


Crankshaft Problems

Journal wear Main bearing wear Rod bearing wear Low oil pressure


Rod Bearing Knock Light, regular rapping noise with the

engine floating Loudest after warm-up Caused by wear and excessive rod

bearing-to-crankshaft clearance To locate, short out or disconnect the

spark plug wires, one at a time The knocking bearing may quiet down

when its cylinder is disabled


Main Bearing Knock

Similar to rod bearing knock, but slightly deeper in pitch

More pronounced when the engine is under load

Worn bearings and journals are letting the crankshaft move up and down

Usually reduces oil pressure


Main Bearing Knock

To verify, remove the oil pan and pressure test the lubrication system

Excessive oil flowing out of one or more of the main bearings implies too much bearing clearance

If the crankshaft is not worn, the bearing inserts may be replaced


Excess Crankshaft End Play

Caused by a worn main thrust bearing May produce a deep knock when

applying or releasing the clutch On an automatic transmission, a single

thud or knock may occur during acceleration or deceleration


Broken Engine Mounts Allow the engine to move in the vehicle To check:

open the hood engage the parking brake shift transmission into drive or into gear with the brakes on, slowly increase

engine speed or release the clutch pedal if the engine moves excessively, the

mounts may be broken


Broken Engine Mounts


Charts list possible problems and needed repairs

Refer to the chart when you have difficulty locating or correcting an engine mechanical problem

chapter 48 engine problems

Documents

broken engine

compression

compression

readings repeat

permission

worn rings

cylinder goodheart

noise