Engine Problem Diagnosis and Tune-Up

2. Chapter 19 Engine Problem Diagnosis and Tune-Up

3. Objectives • Describe a minor tune-up and a major tune-up. • List tune-up safety rules. • List items to look for in a preliminary inspection. • Perform a current starter draw test.

4. Objectives • Perform dry and wet compression tests and analyze the results. • Perform a cylinder leakage test and analyze the results. • Perform a vacuum test and analyze the results.

5. Objectives • Perform a cylinder balance test and analyze the results. • Describe valve adjustment. • List general tune-up rules.

6. What Is a Tune-Up? • Engine tune-up returns engine to peak performance after part wear and deterioration • Tune-up involves • Replacing worn parts • Performing basic service tasks • Making adjustments

7. Minor tune-up is preventative maintenance Performed when engine is in good condition Engine has little or no wear Minor Tune-Up

8. Minor Tune-Up (Cont.) • Visually inspect for problems • Listen for abnormal noises • Check condition of engine oil and coolant

9. Minor Tune-Up (Cont.) • Check for trouble codes in computer • Replace distributor cap, rotor, and spark plugs (older, high-mileage vehicles) • Check and adjust ignition timing • Replace air and fuel filters • Make fuel system adjustments where applicable

10. Minor Tune-Up (Cont.) • Clean throttle body, idle air bypass, and EGR system • Test and service emission control system • Fill all fluid reservoirs to correct level • Road test the vehicle

11. Major Tune-Up • Major tune-up is done when systems or engine is in poor condition and includes • All parts of minor tune-up • Diagnostic tests to determine what should be done to bring vehicle back to good operating condition

12. Tune-Up Safety • Engage emergency brake and block wheels when engine is to be running • Place exhaust hose over tailpipe when running engine in enclosed shop • Keep clothing, hands, tools, and equipment away from moving parts • Disconnect battery when recommended • Be careful not to touch hot exhaust manifold

13. Tune-Up Safety (Cont.) • Keep test equipment leads away from exhaust manifolds, fan, and belts • Wear eye protection when blowing debris from parts or when working near engine fan • Keep fire extinguisher handy, especially during fuel system tests and repairs • With diesel engine, disable injection pump when removing injection line

14. Preliminary Inspection • Look for problems with • Battery • Air cleaner • Fuel system • Belts and hoses • Poor electrical connections • Fix problems before proceeding with tune-up

15. Evaluating the Engine and Its Systems • If scan tool indicates problem with oxygen sensor, remove and inspect sensor • Note color of tip of oxygen sensor • Color can indicate condition of engine and support systems

16. Evaluating the Engine and Its Systems (Cont.) (Tomco, Inc.)

17. Evaluating the Engine and Its Systems (Cont.) • If engine is running too hot or cold, measure operating temperature • Use engine analyzer or handheld tester to check for blown head gasket • To find hard-to-locate oil and coolant leaks, add dye and use a black light

18. Cranking Balance Test • Cranking balance testfinds cylinders with low compression • Monitors current drawn by starter motor during complete turn of crankshaft • Low current draw indicates that starter is not being loaded enough by compression stroke

19. Compression Test • Compression test determines engine’s mechanical condition • Low compression may be caused by • Burned valve or valve seat • Physical engine damage • Blown head gasket • Worn rings or cylinders • Valve train troubles • Jumped timing chain or belt

20. Compression Test—Gasoline Engine • Remove all spark plugs • Block open throttle plates • Disable ignition system • Disable fuel injection system • Screw compression gauge into spark plug hole • Crank engine and let it rotate for about six compression strokes

21. Compression Test—Gasoline Engine (Cont.) • Write down readings for each cylinder • Compare readings to specifications (Snap-on Tool Corp.)

22. Compression Test—Diesel Engine • Procedure is similar to compression test for gasoline engine • Do not use compression gauge intended for gasoline engine on diesel engine • Diesel compression gauge must read up to 600 psi (4200 kPa)

23. Compression Test Results • Gasoline engine readings should be 125-175 psi (860-1200 kPa) in each cylinder • Diesel engine readings should be 275-400 psi (1900-2750 kPa)

24. Compression Test Results (Cont.) • Look for cylinder pressure variations during compression check

25. Wet Compression Test • Wet compression test should be done on any cylinder with compression reading below specifications

26. Wet Compression Test (Cont.)

27. Cylinder Leakage Test • Cylinder leakage testmeasures air leakage out of engine combustion chamber

28. Vacuum Test • Vacuum test measures intake manifold vacuum (General Motors)

29. Cylinder Balance Test • Cylinder balance test disables spark plug in one cylinder at a time • Tests whether cylinders are firing properly

30. Valve Adjustment • On some engines, valve adjustment involves turning rocker arm adjusting screws (Volvo)

31. Valve Adjustment (Cont.) • On some OHC engines, valve adjustment involves changing shim thickness to alter valve lash (Ford)

32. Tune-Up Parts Replacement • Depending on age and condition of engine, parts may need replacement during tune-up • On newer vehicles, only spark plugs and filters may need replacement • Older vehicles with high mileage may need multiple parts

33. Tune-Up Parts Replacement (Cont.) • Parts that may need replacing include • Spark plugs • Spark plug wires • Distributor parts • Fuel system parts • Emission control parts

34. Tune-Up Adjustments • Adjustments needed will vary with make, model, and condition of vehicle • Most common adjustments include • Spark plug gap • Pickup coil air gap • Ignition timing or injection timing • Idle speed

35. Tune-Up Adjustments (Cont.) (Snap-on Tool Corp.)

36. General Tune-Up Rules • Gather information about performance of engine • Use professional, high-quality tools and equipment • Make sure engine has warmed to full operating temperature • Refer to service information or emission sticker for specifications and procedures

37. General Tune-Up Rules (Cont.) • Use quality parts • Keep service records • Complete basic maintenance service • Inform customer about tune-up intervals • Road test the vehicle when tune-up is complete

38. Diesel maintenance involves Replacing air filter element Cleaning, draining, or replacing fuel filters Adjusting engine idle speed and throttle cable Inspecting engine and related systems Checking injection timing Changing engine oil and oil filter Servicing emission control systems periodically Diesel Engine Tune-Up(Maintenance)

39. Review Questions A major tune-up consists of a minor tune-up plus which of the following? • Oil change • Coolant change • Battery recharge • Diagnostic tests Answer: D. Diagnostic tests

40. Review Questions When working on a diesel engine, disable the ____. Answer: injection pump

41. Review Questions True or False? Checking for fuel system leaks is part of the preliminary inspection. Answer: True

42. Review Questions A cranking balance test will locate cylinders with ____ compression. Answer: low

43. Review Questions True or False? A wet compression test is used to locate defective valves. Answer: False. A wet compression test is used to locate defective rings.

44. Review Questions In a(n) ____ test, shop air is pumped into a cylinder and a pressure gauge is used to measure air leakage. Answer: cylinder leakage

45. Review Questions What would cause a vacuum gauge to show higher than normal readings while idling in neutral? • Burned exhaust valve • Burned intake valve • Worn oil rings • None of the above. Answer: D. None of the above.

46. Review Questions What test is commonly performed to find out if individual cylinders are firing properly? Answer: Cylinder balance test

47. Review Questions In some ____ engines, valves must be adjusted by changing the shim thickness. Answer: OHC

48. Review Questions True or False? Diesel engines should be tuned up at regular intervals, just like gasoline engines. Answer: False. Diesel engines do not require periodic tune-ups.