1. Engine Mechanical Testing
CHAPTER 10
Engine Mechanical Testing

2. Introduction
Mechanical condition of engine must be in good working order for engines to work properly and efficiently.
Mechanical testing is performed to:
Diagnose major work needed
Better advise customers on repairs

3. Engine Mechanical Testing (1 of 8)
Series of tests to assess mechanical condition of engine
Start broad and narrow down.
Identify location and cause of fault.

4. Engine Mechanical Testing (2 of 8)
Start with good visual inspection.
Next use tools and equipment.

5. Engine Mechanical Testing (3 of 8)
Compression tester is used when suspicion of low compression.

6. Engine Mechanical Testing (4 of 8)
Vacuum gauge measures amount of vacuum an engine can generate.

7. Engine Mechanical Testing (5 of 8)
Pressure transducer measures engine vacuum or pressure.
Displays graphically

8. Engine Mechanical Testing (6 of 8)
Cylinder leakage tester pumps air into cylinder and measures percentage of air leaking from cylinder.

9. Engine Mechanical Testing (7 of 8)
Scan tool communicates to vehicle’s computers through data link connector.
DLC

10. Engine Mechanical Testing (8 of 8)
Stethoscope listens to noises in vehicles.
Standard
Electronic

11. Fluid Leaks (1 of 8) Checking happens during all routine maintenance.
Customer often complains of fluid spots.
Inspect engine for leaks before engine repair.

12. Fluid Leaks (2 of 8) Color of leak clue to source
Black fluid could be engine oil or gear lube.
Reddish-orange or green fluid could be anti-freeze.
Red fluid could be transmission or power steering fluid.

13. Fluid Leaks (3 of 8) Smell also provides clues.
Fuel and brake fluid have different scents.

14. Fluid Leaks (4 of 8) Gravity causes fluid to be pulled downward.
Always inspect all the way up.

15. Fluid Leaks (5 of 8)
Several processes can be used to discover origin of leak.
Pressure wash, clean, and reinspect.
Use fluorescent dye.
Pressure test cooling system if coolant leak suspected.

16. Fluid Leaks (6 of 8)
Most leaks can be found via a thorough visual inspection.
Light and mirror
Top of engine, under the hood
Under vehicle
Remove covers/heat shields.

17. Fluid Leaks (7 of 8)
After leak is identified, start engine and perform visual inspection again.
Be extremely careful around moving parts.

18. Fluid Leaks (8 of 8) Use of fluorescent dye might be needed.
Once the dye has circulated, inspect engine for leaks.
Special glasses might be required to enhance the fluorescent dye.

19. Cranking Sound Diagnosis Overview (1 of 3)
Noises offer insight into engine’s condition.
Cranking sound diagnosis can identify whether compression is the same across all cylinders.
Compression is one of five critical requirements for cylinders to operate properly.

20. Cranking Sound Diagnosis Overview (2 of 3)
Disassemble engine before performing cranking sound diagnosis.
Noise could be:
Misaligned starter
Spun crankshaft
Low-compression cylinder
No-compression condition
Bent valves
Broken timing belt

21. Cranking Sound Diagnosis Overview (3 of 3)
Engine will make rhythmic cranking sound if compression is same on all cylinders.
Train your ear to pick up different compression sounds.

22. Cranking Sound Diagnosis: Vacuum Testing (1 of 4)
Vacuum gauges determine engine’s general condition.

23. Cranking Sound Diagnosis: Vacuum Testing (2 of 4)
Outside pressure and vacuum
Intake manifold
Good reading is 17" to 21".
Pressure traces see how cylinders are functioning.

24. Cranking Sound Diagnosis: Vacuum Testing (3 of 4)
Vacuum gauges, instructions, and readings are calibrated at sea level.
Must compensate when testing above sea level
Vacuum depends on piston rings, valves, ignition timing, and fuel.

25. Cranking Sound Diagnosis: Vacuum Testing (4 of 4)
Pressure transducer and lab scope are similar to vacuum gauge.
More accurate
View graphically

26. Cylinder Power Balance Test Overview (1 of 3)
Two purposes
Identifies which cylinders are not operating properly
General indicator of overall health of cylinders

27. Cylinder Power Balance Test Overview (2 of 3)
After problem isolated, next determine issue.
Mechanical
Related to compression or ignition
Fuel-related

28. Cylinder Power Balance Test Overview (3 of 3)
Several ways to perform power balance test
Easiest determined by PCM, ease of accessing required components, and tools available.
Determine whether to disable the ignition or fuel to each cylinder.
Shutting down fuel is preferable if working on engine.

29. Cranking and Running Compression Tests (1 of 8)
High-pressure hose is hand-threaded in spark plug hole, tested, then connected to compression gauge.
Engine is cranked over or started, depending on test.
Crank at least five compression pulses to get accurate reading.

30. Cranking and Running Compression Tests (2 of 8)
Compression gauge reads amount of pressure piston is producing.
Compresses air in cylinder

31. Cranking and Running Compression Tests (3 of 8)
Misfiring or dead cylinder is not caused by ignition or fuel problem.
Measures air pressure as it is compressed in cylinder
Cylinders should all measure within 10% to 15% of each other.

32. Cranking and Running Compression Tests (4 of 8)
Engine at operating temperature, spark plugs removed, battery fully charged, throttle held wide open, and at least five compression pulses made on each cylinder
Will help create maximum compression and accurate readings

33. Cranking and Running Compression Tests (5 of 8)
Engine is running during compression test.
Checks engine’s ability to move air into and out of cylinder
Engine’s ability to breathe

34. Cranking and Running Compression Tests (6 of 8)
Test performed in two parts:
Idle
Snap throttle

35. Cranking and Running Compression Tests (7 of 8)
Idle: engine running, throttle closed, compression pressure half of cranking compression pressure
Snap throttle: engine idling, throttle snapped open and then closed quickly
No change to rpm

36. Cranking and Running Compression Tests (8 of 8)
Test is performed leaving all spark plugs in engine except for cylinder being tested.
Schrader valves use lighter-weight springs than tire Schrader valves.
Not interchangeable

37. Cylinder Leakage Test Overview (1 of 5)
Cylinder leakage test is performed on cylinder with low compression to determine severity of compression leak and leak’s location.

38. Cylinder Leakage Test Overview (2 of 5)
Compressed air is applied to cylinder to show amount of leakage.
Ideal reading is 0%.
Up to 20% is acceptable.

39. Cylinder Leakage Test Overview (3 of 5)
Small leakage past piston rings is okay.
Leakage past one of the valves or the head gasket is not okay.
Leakage = major mechanical engine issue

40. Cylinder Leakage Test Overview (4 of 5)
Several critical steps to ensure tests are accurate
Engine near operating temperature
Ensures oil has been circulated to piston rings
Loosen each spark plug about one turn.

41. Cylinder Leakage Test Overview (5 of 5)
Run engine at 1500 rpm for 10 to 15 seconds.
Blows out chunks of carbon straddling spark plug
Cylinder leakage is measured when piston is on top dead center on compression stroke.
Turn crankshaft to position pistons before pressurizing system.

42. Diagnosing Engine Noise and Vibrations (1 of 3)
Running engines are relatively quiet.
Noises can indicate small issues as well as something majorly wrong.
Investigate unusual noises and build on your experience.

43. Diagnosing Engine Noise and Vibrations (2 of 3)
Mechanic’s stethoscope helps to locate engine noise.
Mechanical or electronic
Mechanical is most common.
Electronic enhances selected sound frequencies.

44. Diagnosing Engine Noise and Vibrations (3 of 3)
Vibrations can be difficult to pinpoint.
From engine or drive train
Best clue is to determine if vibration occurs with engine running irrespective of vehicle movement.

45. Diagnosing Oil Consumption, Coolant Consumption, and Exhaust Color (1 of 3)
Coolant should not have consumption if cooling system is working properly.
Engine oil can have small amount of consumption and be considered normal.

46. Diagnosing Oil Consumption, Coolant Consumption, and Exhaust Color (2 of 3)
Consumption of oil or coolant could be diagnosed by color of exhaust.
Bluish tint: engine oil burning
Blue constant while engine running: rings not sealing due to worn rings or cylinder walls
Blue only when start engine: likely valve steam seal or valve guide issue

47. Diagnosing Oil Consumption, Coolant Consumption, and Exhaust Color (3 of 3)
Consumption diagnosed by color of exhaust (cont’d)
Black: excessively rich fuel mixture
White after engine warmed up: coolant leaking into exhaust
Blown head gasket
Blown intake gasket
Cracked cylinder head
Leaky exhaust gas recirculation cooler on some vehicles

48. Summary (1 of 5)
Appropriate service information is needed to make an accurate diagnosis.
The best source for vehicle service information is the vehicle manufacturer.
Major vehicle components often have identification numbers.

49. Summary (2 of 5)
A systematic mechanical testing and verification process is needed to diagnose and repair an engine problem.
Engine mechanical testing tools include: a compression gauge, vacuum gauge, cylinder leakage tester, and scan tool.
The color of a leaking fluid can assist in identifying the source of a leak.

50. Summary (3 of 5)
During engine cranking, the engine will make an even cranking sound if the compression is even between the cylinders.
A vacuum gauge is used to determine the general condition of an engine.
A cylinder power balance test is used to determine whether all of the engine cylinders are working properly.

51. Summary (4 of 5)
A cranking compression test measures the compressed air pressure in the cylinder.
A running compression test checks the engine’s breathing ability.
A cylinder leakage test is performed on a cylinder with low compression.

52. Summary (5 of 5) A stethoscope can be used to isolate an engine noise.
Exhaust smoke can indicate the source of an engine problem.
An odor can help diagnose an engine problem.
Engine tests must be properly interpreted to correct an engine problem.

53. Credits
Unless otherwise indicated, all photographs and illustrations are under copyright of Jones & Bartlett Learning.