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Similar to Chapter 48 engine problems (10)
Chapter 48 engine problems
- 1. by
Russell Krick
Publisher
The Goodheart-Willcox Co., Inc.
Tinley Park, Illinois
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- 3. 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
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- 4. 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
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- 5. Excessive oil consumption
Excessive crankcase blowby
Noises
Exhaust smoke
Poor performance
Coolant in the oil
Engine seizure
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- 6. Engine Mechanical
Problems
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- 7. Pre-Teardown
Inspection
Run the engine
Look for external problems:
oil leaks
vacuum leaks
part damage
contaminated oil
Listen and watch for problems
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- 8. 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
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- 9. Oil-Fouled Spark Plugs
Indicate internal oil leakage into the
combustion chambers—caused by worn
rings, cylinder walls, or valve seals
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- 10. Oil In Coolant
Causes:
a leak in the radiator oil cooler
head gasket leakage
a cracked block or head
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- 11. 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
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- 12. External Coolant Leaks
Causes:
hose problems
rusted freeze (core) plugs
warped, worn, or damaged parts
Use a pressure tester to locate leaks
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- 13. Engine
Blowby
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- 14. 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
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- 15. Engine Exhaust Leaks
Produce a clicking sound
Causes:
leaking exhaust gaskets
a warped exhaust manifold
loose manifold bolts
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- 16. Engine Exhaust Leaks
The leakage path can be easily seen after
exhaust manifold removal
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- 18. 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
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- 19. 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
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- 21. 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
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- 24. Connect Compression
Gauge
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- 26. Replacing Plugs and
Wires
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- 27. 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
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- 28. 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
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- 29. Wet Compression Test
A. Perform dry test B. Squirt oil into cylinder
C. Measure again
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- 30. 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
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- 31. 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%
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- 32. 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
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- 33. 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
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- 35. Valve Train Problems
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- 36. Burned Valve
Causes an engine miss, a popping sound
at the throttle body or exhaust
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- 37. Worn Valve Guides
and Stems
Causes tapping noise,
oil consumption, spark
plug fouling, or stem
breakage
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- 38. 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
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- 39. Valve Breakage
Caused by valve stem fatigue or by a
broken or weak valve spring
Usually causes severe piston and
cylinder damage
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- 40. Stuck Valve
Valve stem rusts or corrodes and locks
in the valve guide
May happen when the engine sits in
storage
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- 41. 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
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- 42. Worn Timing Chain
Causes reduced compression and power
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- 43. 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
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- 44. Camshaft Problems
Worn cam lobes
Worn journals
Broken cams
Worn distributor drive gear
Loose or worn fuel pump drive
eccentric
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- 45. Cam Lobe Wear
Reduces valve lift and power output
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- 46. 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
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- 47. Valve Train Clearance
Excess clearance can produce noise
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- 48. 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
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- 49. Piston Knock (Slap)
Loud, metallic knock that is loudest when
the engine is cold
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- 50. 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
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- 51. Worn Rings and
Cylinder
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- 52. Worn Ring Grooves
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- 53. Burned Piston
Results from prolonged preignition or
detonation
Causes low compression, blowby,
smoking, and rough idle
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- 55. Crankshaft Problems
Journal wear
Main bearing wear
Rod bearing wear
Low oil pressure
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- 56. 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
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- 57. 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
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- 58. 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
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- 59. 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
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- 60. 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
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- 61. Broken Engine Mounts
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- 62. Charts list possible problems and
needed repairs
Refer to the chart when you have
difficulty locating or correcting an
engine mechanical problem
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