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Diagnosis And Testing: Mechanical

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ENGINE MECHANICAL DIAGNOSIS CHART

CONDITION POSSIBLE CAUSES CORRECTION
ENGINE NOISE 1. Worn accessory drive belt 1. Check for damage and/or alignment.
2. Worn water pump 2. Check for possible coolant leak. If ok, Check the pulley and input shaft for wear. Replace as necessary.
3. Worn generator 3. Check the pulley for wear. Spin the armature. Replace as necessary.
4. Idler/Tensioner pulley 4. Check pulleys. Verify bearing noise. Replace as necessary.
5. Power steering pump 5. Check the pulley and input shaft for wear. Replace as necessary.
6. Flywheel/Flexplate 6. Check for wear or possible cracking. Check bolts. Repair as necessary.
NOISY VALVES/LIFTERS 1. High or low oil level in crankcase 1. Check for correct oil level. Adjust oil level by draining or adding as needed.
2. Thin or diluted oil 2. Change oil. Refer to ENGINE OIL AND FILTER CHANGE  .
3. Low oil pressure 3. Check engine oil level. If ok, perform engine oil pressure test. Refer to CHECKING ENGINE OIL PRESSURE  .
4. Excessive aeration of the oil 4. Change the engine oil and filter.
5. Air trapped in the lash adjuster(s) 5. Follow the "Lifter Purge Guideline" shown below.
6. Exhaust manifold leak 6. Inspect exhaust manifolds, fasteners, and gaskets for possible leaks.
7. Bent push rod(s) 7. Install new push rods.
8. Worn rocker arms 8. Inspect oil supply to rocker arms and replace worn arms as needed.
9. Debris in tappets/lash adjusters 9. Clean/replace hydraulic tappets/lash adjusters.
10. Worn tappets/lash adjusters 10. Install new hydraulic tappets/lash adjusters.
11. Worn valve guides 11. Inspect all valve guides and replace as necessary.
12. Excessive runout of valve seats or valve faces 12. Grind valves and seats.
CONNECTING ROD NOISE 1. Insufficient oil supply 1. Check engine oil level.
2. Low oil pressure 2. Check engine oil level. If ok, Perform engine oil pressure test. Refer to CHECKING ENGINE OIL PRESSURE  .
3. Thin or diluted oil 3. Change oil to correct viscosity. Refer to ENGINE OIL AND FILTER CHANGE  .
4. Excessive connecting rod bearing clearance 4. Measure bearings for correct clearance with plasti-gage. Repair as necessary.
5. Connecting rod journal out of round 5. Replace crankshaft or grind journals.
6. Misaligned connecting rods 6. Replace bent connecting rods.
MAIN BEARING NOISE 1. Insufficient oil supply 1. Check engine oil level.
2. Low oil pressure 2. Check engine oil level. If ok, Perform engine oil pressure test. Refer to CHECKING ENGINE OIL PRESSURE  .
3. Thin or diluted oil 3. Change oil to correct viscosity.
4. Excessive main bearing clearance 4. Measure bearings for correct clearance. Repair as necessary.
5. Excessive end play 5. Check crankshaft thrust bearing for excessive wear on flanges.
6. Crankshaft main journal out of round or worn 6. Grind journals or replace crankshaft.
7. Loose flexplate/flywheel or torque converter 7. Inspect crankshaft, flexplate/flywheel and bolts for damage. Tighten to correct torque.
LOW OIL PRESSURE 1. Low oil level 1. Check oil level and fill if necessary.
2. Faulty oil pressure sending unit 2. Install new sending unit.
3. Clogged oil filter 3. Install new oil filter.
4. Worn oil pump 4. Replace oil pump assembly.
5. Thin or diluted oil 5. Change oil to correct viscosity.
6. Excessive bearing clearance 6. Measure bearings for correct clearance.
7. Oil pump relief valve stuck 7. Remove valve to inspect, clean and reinstall.
8. Oil pickup tube loose, broken, bent or clogged 8. Inspect oil pickup tube and pump, and clean or replace if necessary.
9. Oil pump cover warped or cracked 9. Install new oil pump.
10. Make up air hose may be plugged or Positive Crankcase Ventilation (PCV) valve may be inoperative 10. Check make up air hose to assure there is no blockage and verify PCV valve for proper function.
OIL LEAKS 1. Misaligned or deteriorated gaskets/seals 1. Replace gasket/seal.
2. Loose fastener, broken or porous metal part 2. Tighten, repair or replace the part.
3. Front or rear crankshaft oil seal leaking 3. Replace seal.
4. Leaking oil gallery plug or cup plug 4. Remove and reseal threaded plug. Replace cup style plug.
EXCESSIVE OIL CONSUMPTION OR SPARK PLUGS OIL FOULED 1. Defective valve stem seal(s) 1. Repair or replace seal(s).
2. Worn or broken piston rings 2. Hone cylinder bores. Install new rings.
3. Scuffed pistons/cylinder walls 3. Hone cylinder bores and replace pistons as required.
4. Carbon in oil control ring groove 4. Remove rings and de-carbon piston.
5. Worn valve guides 5. Inspect/replace valve guides as necessary.
6. Piston rings fitted too tightly in grooves 6. Remove rings and check ring end gap and side clearance. Replace if necessary.
7. PCV system not operating properly 7. Replace PCV valve and check all PCV plumbing for leaks or blockages.

Lifter Purge Guideline

  1. Warm engine to standard idle conditions.
    NOTE:

    Engine noise may be in the form of a clicking, chatter, or clattering noise.

  2. Listen to the engine for 30 to 60 seconds with the hood up and the engine cover removed.
  3. If noise is present, de-aeration of the lifters is required.
  4. Run the engine between 2000 and 3000 RPM for three to five minutes.
  5. Return the engine to standard idle speed for 30 to 60 seconds.
  6. Evaluate noise. If noise is present, repeat the run an additional 4 cycles.
    NOTE:

    The standard drive cycle will be about 10 - 15 miles of non- stop, combined highway and city driving.

  7. If noise is present, take the vehicle on a standard drive cycle.
    NOTE:

    Use a feeler gauge to verify clearance is present between the lifter and cam base circle.

  8. Evaluate the noise. If noise present, follow standard service procedure for lifter repairs or noise conditions.
  9. Evaluate lifters for sponginess, check valve defects, and clearance.
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