halderman ch026 lecture

© 2011 Pearson Education, Inc.All Rights Reserved

Automotive Technology, Fourth EditionJames Halderman

ENGINE CONDITION DIAGNOSIS

26

26 ENGINE CONDITION DIAGNOSIS



ObjectivesObjectives

• The student should be able to:– Prepare for ASE Engine Performance (A8)

certification test content area “A” (General Engine Diagnosis).

– List the visual checks to determine engine condition.

– Discuss engine noise and its relation to engine condition.




ObjectivesObjectives

• The student should be able to:– Describe how to perform a dry and a wet

compression test. – Explain how to perform a cylinder leakage

test.




TYPICAL ENGINE-TYPICAL ENGINE-RELATEDRELATED

COMPLAINTSCOMPLAINTS




Typical-Engine Related ComplaintsTypical-Engine Related Complaints

• Excessive oil consumption• Engine misfiring• Loss of power• Smoke from engine or exhaust• Engine noise




ENGINE SMOKE ENGINE SMOKE DIAGNOSISDIAGNOSIS




Engine Smoke DiagnosisEngine Smoke Diagnosis

• Note: White smoke can also be created when automatic transmission fluid (ATF) is burned. A common source of ATF getting into the engine is through a defective vacuum modulator valve on older automatic transmissions.




Engine Smoke DiagnosisEngine Smoke Diagnosis




Figure 26-1 Blowby gases coming out of the crankcase vent hose. Excessive amounts of combustion gases flow past the piston rings and into the crankcase.




Figure 26-2 White steam is usually an indication of a blown (defective) cylinder head gasket that allows engine coolant to flow into the combustion chamber where it is turned to steam.




THE DRIVER IS YOURTHE DRIVER IS YOURBEST RESOURCEBEST RESOURCE




The Driver Is Your Best ResourceThe Driver Is Your Best Resource

• Before diagnosis, always ask driver following questions:– When did the problem first occur?





• Before diagnosis, always ask driver following questions:– Under what conditions does it occur?

1. Cold or hot?2. Acceleration, cruise, or deceleration?





• Before diagnosis, always ask driver following questions:– Under what conditions does it occur?

3. How far was it driven?4. What recent repairs have been performed?




VISUAL CHECKSVISUAL CHECKS




Visual ChecksVisual Checks

• Oil Level and Condition1. Oil level2. Oil condition

a. Gasoline present in engine oil?b. Coolant (water) in oil?c. Oil gritty?





• Coolant Level and Condition– Level in recovery container within correct

limits?– Concentration of antifreeze sufficient for

proper protection?





• Coolant Level and Condition– Leakage in cooling system?– Clogged sections of radiator?





• Coolant Level and Condition– Fan clutch, fan, and coolant pump drive

belt working properly?





• Oil Leaks– Find source of oil leaks

• Clean engine or area around suspected leak






• If leak not visible, use white talcum powder






• Add fluorescent dye to oil (works best with clean oil)




Figure 26-3 What looks like an oil pan gasket leak can be a rocker cover gasket leak. Always look up and look for the highest place you see oil leaking; that should be repaired first.




Figure 26-4 The transmission and flexplate (flywheel) were removed to check the exact location of this oil leak. The rear main seal and/or the oil pan gasket could be the cause of this leak.




Figure 26-5 Using a black light to spot leaks after adding dye to the oil.




ENGINE NOISE ENGINE NOISE DIAGNOSISDIAGNOSIS




Engine Noise DiagnosisEngine Noise Diagnosis

• Causes of Deep Engine Knock– Valves clicking– Torque converter– Cracked flex plate





• Causes of Deep Engine Knock– Loose or defective drive belts or tensioners– Piston pin knock– Piston slap





• Causes of Deep Engine Knock– Timing chain noise– Rod-bearing noise– Main-bearing knock




Figure 26-6 An accessory belt tensioner. Most tensioners have a mark that indicates normal operating location. If the belt has stretched, this indicator mark will be outside of the normal range. Anything wrong with the belt or tensioner can cause noise.




Figure 26-7 A cracked exhaust manifold on a Ford V-8.




OIL PRESSURE OIL PRESSURE TESTINGTESTING




Oil Pressure TestingOil Pressure Testing

• Operate engine until normal operating temperature achieved

• With engine off, thread pressure gauge into oil pressure sending unit




Oil Pressure TestingOil Pressure Testing

• Start engine and observe gauge• Compare test results with

manufacturer’s recommended oil pressure




Figure 26-8 To measure engine oil pressure, remove the oil pressure sending (sender) unit usually located near the oil filter. Screw the pressure gauge into the oil pressure sending unit hole.




Figure 26-9 The paper test involves holding a piece of paper near the tailpipe of an idling engine. A good engine should produce even, outward puffs of exhaust. If the paper is sucked in toward the tailpipe, a burned valve is a possibility.




OIL PRESSUREOIL PRESSUREWARNING LAMPWARNING LAMP




Oil Pressure Warning LampOil Pressure Warning Lamp

• Usually lights when oil pressure less than 4 to 7 PSI

• If lamp is on, stop engine immediately




COMPRESSION TESTCOMPRESSION TEST




Compression TestCompression Test

• Engine can lose compression by leakage through one or more of these routes– Intake or exhaust valve– Piston rings (or piston, if there is a hole)– Cylinder head gasket





• Performing Compression Test– Remove all spark plugs– Block open the throttle– Thread compression gauge into one spark

plug hole





• Performing Compression Test– Crank engine through four compression

strokes– Record highest readings and compare for

each cylinder




Figure 26-10 A two-piece compression gauge set. The threaded hose is screwed into the spark plug hole after removing the spark plug. The gauge part is then snapped onto the end of the hose.




Figure 26-11 Use a vacuum or fuel line hose over the spark plug to install it without danger of cross-threading the cylinder head.




WET COMPRESSION WET COMPRESSION TESTTEST




Wet Compression TestWet Compression Test

• Use oil to help seal around piston rings• Perform compression test again




Figure 26-12 Badly burned exhaust valve. A compression test could have detected a problem, and a cylinder leakage test ( leak-down test) could have been used to determine the exact problem.




RUNNING (DYNAMIC)RUNNING (DYNAMIC)COMPRESSION TESTCOMPRESSION TEST




Running (Dynamic) Compression TestRunning (Dynamic) Compression Test

• Done with engine running rather than during engine cranking

• Look for variations in running compression values among cylinders





• Performing a Running Compression Test– Remove just one spark plug at a time– Use jumper wire to ground spark plug wire





• Performing a Running Compression Test– Start engine– Push pressure release on gauge– Read compression





• Performing a Running Compression Test– Increase engine speed to 2,000 RPM– Read compression again– Repeat with other cylinders




CYLINDER LEAKAGE CYLINDER LEAKAGE TESTTEST




Cylinder Leakage TestCylinder Leakage Test

• Have engine at normal operating temperature

• Have cylinder being tested at TDC of compression stroke

• Calibrate cylinder leakage unit per manufacturer’s instructions





• Inject air into cylinders one at a time• Evaluate results

– Less than 10% leakage: good





• Evaluate results– More than 30% leakage: definite problem

• Check source of air leakage




Figure 26-13 A typical handheld cylinder leakage tester.




Figure 26-14 A whistle stop used to find top dead center. Remove the spark plug and install the whistle stop, then rotate the engine by hand. When the whistle stops making a sound, the piston is at the top.




CYLINDER POWERCYLINDER POWERBALANCE TESTBALANCE TEST




Cylinder Power Balance TestCylinder Power Balance Test

• Determines if all cylinders are contributing power equally

• Cylinder with least RPM drop not producing its share of power




POWER BALANCEPOWER BALANCETEST PROCEDURETEST PROCEDURE




Power Balance Test ProcedurePower Balance Test Procedure

• Acceptable method of canceling cylinders– Ground secondary current for each cylinder– Will work on all types of ignition systems,

including distributorless




Figure 26-15 Using a vacuum hose and a test light to ground one cylinder at a time on a distributorless ignition system. This works on all types of ignition systems and provides a method for grounding out one cylinder at a time without fear of damaging any component. To avoid possible damage to the catalytic converter, do not short out a cylinder for longer than five seconds.




VACUUM TESTSVACUUM TESTS




Vacuum TestsVacuum Tests

• Vacuum: pressure below atmospheric pressure

• Measured in inches (or millimeters) of mercury (Hg)

• Engine in good mechanical condition will run with high manifold vacuum





• Cranking Vacuum Test– Determines if piston rings and valves

properly sealing– Disable the ignition or fuel injection





• Cranking Vacuum Test– Connect vacuum gauge to manifold

vacuum source– Crank engine while observing vacuum

gauge





• Cranking Vacuum Test– Causes of low cranking vacuum:

• Too slow a cranking speed• Worn piston rings





• Cranking Vacuum Test– Causes of low cranking vacuum:

• Leaking valves• Excessive amounts of air bypassing throttle

plate





• Idle Vacuum Test– Properly condition engine should idle with

vacuum of 17–21 in. Hg– Engine vacuum readings vary with altitude




Figure 26-16 An engine in good mechanical condition should produce 17 to 21 in. Hg of vacuum at idle at sea level.





• Low and Steady Vacuum– Most common causes

• Retarded ignition timing• Retarded cam timing




Figure 26-17 A steady but low reading could indicate retarded valve or ignition timing.





• Fluctuating Vacuum– Common causes

• Sticking valve• Burned valves or weak valve springs• Unequal fuel mixture




Figure 26-18 A gauge reading with the needle fluctuating 3 to 9 in. Hg below normal often indicates a vacuum leak in the intake system.




Figure 26-19 A leaking head gasket can cause the needle to vibrate as it moves through a range from below to above normal.




Figure 26-20 An oscillating needle 1 or 2 in. Hg below normal could indicate an incorrect air-fuel mixture (either too rich or too lean).




Figure 26-21 A rapidly vibrating needle at idle that becomes steady as engine speed is increased indicates worn valve guides.




Figure 26-22 If the needle drops 1 or 2 in. Hg from the normal reading, one of the engine valves is burned or not seating properly.




Figure 26-23 Weak valve springs will produce a normal reading at idle, but as engine speed increases, the needle will fluctuate rapidly between 12 and 24 in. Hg.




Figure 26-24 A steady needle reading that drops 2 or 3 in. Hg when the engine speed is increased slightly above idle indicates that the ignition timing is retarded.




Figure 26-25 A steady needle reading that rises 2 or 3 in. Hg when the engine speed is increased slightly above idle indicates that the ignition timing is advanced.




Figure 26-26 A needle that drops to near zero when the engine is accelerated rapidly and then rises slightly to a reading below normal indicates an exhaust restriction.




EXHAUST RESTRICTION EXHAUST RESTRICTION TESTTEST




Exhaust Restriction TestExhaust Restriction Test

• Common Causes of Restricted Exhaust– Clogged catalytic converter– Clogged or restricted muffler– Damaged or defective piping




TESTING BACK TESTING BACK PRESSURE WITH A PRESSURE WITH A VACUUM GAUGEVACUUM GAUGE




Testing Back Pressure with a Vacuum Testing Back Pressure with a Vacuum GaugeGauge

• Back pressure: increased pressure in exhaust system because of restriction

• Results in gradual drop in manifold vacuum

• Car becomes undriveable




TESTING BACK TESTING BACK PRESSURE WITH A PRESSURE WITH A PRESSURE GAUGEPRESSURE GAUGE




Testing Back Pressure with a Pressure Testing Back Pressure with a Pressure GaugeGauge

• With an oxygen sensor• With exhaust gas recirculation (EGR)

valve• With air-injection reaction (AIR) check

valve




Figure 26-27 A technician-made adapter used to test exhaust system back pressure.




DIAGNOSING HEADDIAGNOSING HEADGASKET FAILUREGASKET FAILURE




Diagnosing Head Gasket FailureDiagnosing Head Gasket Failure

• Ways of Diagnosing Head Gasket Failure– Exhaust gas analyzer– Chemical test– Bubbles in coolant– Excessive exhaust steam




Diagnosing Head Gasket FailureDiagnosing Head Gasket Failure

• If head gasket failure indicated:– Check head gasket– Check sealing surfaces—for warpage– Check castings—for cracks




Figure 26-28 A tester that uses a blue liquid to check for exhaust gases in the exhaust, which would indicate a head gasket leak problem.




DASH WARNING DASH WARNING LIGHTSLIGHTS




Dash Warning LightsDash Warning Lights

• Oil (Engine) Light– When light comes on, shut off the engine

immediately– Check oil level and condition– Oil level okay: possible serious engine

problem





• Coolant Temperature Light– If light comes on while driving:

• Turn off air conditioning and turn on heater• Raise engine speed in neutral to increase

coolant circulation





• Coolant Temperature Light– If light comes on while driving:

• Turn engine off and allow to cool• Do not continue driving with light on




COMPRESSION TEST 1 The tools and equipment needed to perform a compression test include a compression gauge, an air nozzle, and the socket ratchets and extensions that may be necessary to remove the spark plugs from the engine.




COMPRESSION TEST 2 To prevent ignition and fuel-injection operation while the engine is being cranked, remove both the fuelinjection fuse and the ignition fuse. If the fuses cannot be removed, disconnect the wiring connectors for the injectors and the ignition system.




COMPRESSION TEST 3 Block open the throttle (and choke, if the engine is equipped with a carburetor). Here a screwdriver is being used to wedge the throttle linkage open. Keeping the throttle open ensures that enough air will be drawn into the engine so that the compression test results will be accurate.




COMPRESSION TEST 4 Before removing the spark plugs, use an air nozzle to blow away any dirt that may be around the spark plug. This step helps prevent debris from getting into the engine when the spark plugs are removed.




COMPRESSION TEST 5 Remove all of the spark plugs. Be sure to mark the spark plug wires so that they can be reinstalled onto the correct spark plugs after the compression test has been performed.




COMPRESSION TEST 6 Select the proper adapter for the compression gauge. The threads on the adapter should match those on the spark plug.




COMPRESSION TEST 7 If necessary, connect a battery charger to the battery before starting the compression test. It is important that consistent cranking speed be available for each cylinder being tested.




COMPRESSION TEST 8 Make a note of the reading on the gauge after the first “puff,” which indicates the first compression stroke that occurred on that cylinder as the engine was being rotated. If the first puff reading is low and the reading gradually increases with each puff, weak or worn piston rings may be indicated.




COMPRESSION TEST 9 After the engine has been cranked for four “puffs,” stop cranking the engine and observe the compression gauge.




COMPRESSION TEST 10 Record the first puff and this final reading for each cylinder. The final readings should all be within 20% of each other.




COMPRESSION TEST 11 If a cylinder(s) is lower than most of the others, use an oil can and squirt two squirts of engine oil into the cylinder and repeat the compression test. This is called performing a wet compression test.




COMPRESSION TEST 12 If the gauge reading is now much higher than the first test results, then the cause of the low compression is due to worn or defective piston rings. The oil in the cylinder temporarily seals the rings which causes the higher reading.

halderman ch026 lecture

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engine condition diagnosis

engine smoke diagnosis

engine noise diagnosis

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