Troubleshooting diesel engines by sound

Understanding these four engine sounds will make it easier to identify engine problems.

When the engine fails, different phenomena will occur in the vehicle, and abnormal noise is one of them. Abnormal noise represents certain faults. If not resolved in time, it will accelerate the wear of parts and even cause accidental damage. Therefore, timely troubleshooting and proper maintenance are very necessary.

Manually check for abnormal engine noise

Look: Observe possible faulty engine structures, assemblies and parts to determine engine operation.

Touch: Touch potentially faulty components, check their temperature, vibration, etc., and analyze the matching tightness of the components, bearing gap size, balance weight of the components, etc.

Test: Fully display the fault phenomenon through various testing methods, such as honking the horn, turning on the ignition switch or light switch, and turning off the spark plug. The rated speed of the engine can be quickly increased or decreased, and if necessary, new original components or parts can be replaced for comparative testing.

Listen: Based on the different working conditions of the engine, the noise and noise patterns of different parts, determine what is normal and what is abnormal.

If the engine noise is abnormal through the above four steps, the next step is to identify the fault. We’ve collected a “Four Listens” method that will guide you in identifying engine troubles with ease.

Valve foot noise

Phenomenon

  1. When the diesel engine is cold started, noise is likely to occur.
  2. The noise of the valve foot has nothing to do with the speed. It only makes a crisp sound occasionally and then disappears. If it occurs frequently, it can cause serious trouble.
  3. Noise occurs when some cylinders are not working. After the noise disappears, the Cylinder returns to normal.

Reasons

  1. The valve seat in the cylinder head is loose and the contraction range is too small.
  2. Using a valve seat made of improper material can result in an excessively low coefficient of thermal expansion.

Diagnostics and troubleshooting

  1. If noise occurs, a single cylinder does not work. After the noise disappears, the cylinder returns to normal. It can be diagnosed as loose valve seat of non-working cylinder.

  2. Use a cylinder pressure gauge to measure the pressure of each cylinder. Low-pressure cylinders are abnormally noisy cylinders.

Camshaft noise

Phenomenon

  1. When the diesel engine is running at medium speed, heavy noise is emitted from the side of the camshaft of the cylinder block, and the chaotic noise is unclear at high speed.

  2. When the single cylinder fuel is cut off, the noise does not change.

  3. Camshaft bearings are accompanied by vibration.

Reasons

  1. The grape is too big and there is looseness between the camshaft bearing and journal.

  2. The camshaft bearing is loose or the bearing alloy has excessive ablation, peeling or wear.

  3. The axial clearance of the camshaft is too large or the camshaft is bent.

Diagnostics and troubleshooting

  1. Use a stethoscope to diagnose the cylinder of the diesel engine at maximum speed. If the noise is strong and accompanied by vibration, you can be sure it is coming from the diagnosed bearing.
  2. If the noise remains the same during the fuel cutoff, you can slowly replace the throttle. If the idle sound is clear, the medium speed sound is obvious, and the high speed sound is weakened due to messiness, it can be determined that the camshaft axial clearance is too large or the bearing is loose.

Valve leaks

Phenomenon

  1. When a valve leakage failure occurs, the diesel engine will be difficult to start, the exhaust pipe will blow, smoke will appear, fuel consumption will increase, and abnormal sounds will be made.

Reasons

  1. The surface between the valve and the valve seat ring is worn, ablated, or poorly sealed, causing air leakage.
  2. There is carbon deposit on the surface of the valve and valve seat ring, and the valve cannot be closed tightly, causing air leakage.
  3. The gap between the valve and the valve guide is too large, causing the valve stem to shake, resulting in loose valve closing and air leakage.
  4. The valve stem is stuck in the valve guide or is difficult to move, and the valve cannot move up or down.
  5. The valve spring has no elasticity or the spring has fallen off.

Diagnostics and troubleshooting

  1. After troubleshooting the ignition system and fuel system, measure the cylinder pressure or intake manifold vacuum if still unsure. If the pressure of the valve leaking cylinder is lower than that of other cylinders, it can be accurately determined to be a valve leaking failure.

Hydraulic lifter noise

Phenomenon

  1. When the diesel engine is running, a rhythmic noise occurs, which is typical at idle speed, but decreases or disappears at medium or high speeds.

Reasons

  1. If the diesel engine lubricating oil level is too high or too low, foaming engine oil will enter the hydraulic lifter, producing elastic gas and abnormal noise.
  2. Lubricant pressure too low.
  3. The oil pump and filter are damaged or damaged, causing air to absorb lubricating oil.
  4. Hydraulic lifter failure.
  5. Use inferior lubricants.

Diagnostics and troubleshooting

  1. Check the engine oil level and fill or replace it as appropriate to ensure the engine oil is adequate.
  2. Check whether the oil pressure is normal and whether the hydraulic lifter is invalid?
  3. Remove the oil pan, check the oil pump, filter or replace the oil pump. Disassemble the valve structure and replace the hydraulic lifter and valve guide.

When abnormal noise occurs in the engine, if the above methods cannot be diagnosed and eliminated, please contact FJT for a better solution.

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