Chapter 48 engine problems

by
Russell Krick

Publisher
The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
© Goodheart-Willcox Co., Inc. Permission granted to reproduce for educational use only

 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 Guides
and 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 when
the 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

More Related Content

What's hot

Viewers also liked

Similar to Chapter 48 engine problems

Chapter 48 engine problems