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

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