Diagnostic aid for spark plugs — based on the example of the BERU Ultra. Take a good look at your spark plug!

1 Optimal spark plug appearance

The insulator nose is of a grey-white/grey-yellow to light red-brown colour. The electrode erosion is low. The thermal value of the spark plug has been chosen correctly. No thermal overload. The mixture and ignition settings are correct, the engine is in good condition.

2 Coked

• Cause:
  incorrect mixture adjustment: mixture too rich, air filter heavily soiled, defective cold starting device. Predominantly used for short journeys. Thermal value of the spark plug too high.
• Effect:
  Poor cold starting behaviour and misfiring due to tracking. In this way unburned fuel can reach the catalytic converter and damage it.
• Rectification:
  Correctly adjust mixture and starting device. Check air filter. Fit new original BERU brand spark plugs.

3 Oiled

• Cause:
  Too much oil in the combustion chamber, oil level is too high, heavily worn piston rings, cylinder or valve guides.
• Effect:
  misfiring or even shorting of the spark plug. Complete failure.
• Rectification:
  Overhaul engine, correct oil mixture, fit new original BERU brand spark plugs.

4 Heavily Worn Electrodes

• Cause:
  Aggressive fuel and oil additives, poor flow conditions in the combustion chamber (possibly due to deposits), engine knocking, thermal overload.
• Effect:
  Prior to total failure (engine damage), loss of performance occurs.
• Rectification:
  Check engine, ignition and mixture, check spark plug tightening torque. Fit new original BERU brand spark plugs.

5 Melted Electrodes

• Cause:
  Thermal overload due to pre-ignition, e.g. due to incorrect ignition timing, combustion residues in the combustion chamber, defective valves, faulty distributor, unsatisfactory fuel quality, incorrectly tightened spark plug.
• Effect:
  Prior to total failure (engine damage), loss of performance occurs.
• Rectification:
  Check engine, ignition and mixture, check spark plug tightening torque. Fit new original BERU brand spark plugs.

6 Glazing

• Cause:
  Additives in the petrol and engine oil form ash type deposits.
• Effect:
  Under sudden full engine load, these deposits are liquefied and become electrically conductive.
• Rectification:
  

7 Melted centre electrode

• Cause:
  Thermal overload due to pre-ignition, e.g. due to incorrect ignition timing, combustion residues in the combustion chamber, defective valves, faulty distributor, unsatisfactory fuel quality, thermal value may be too low, incorrect spark plug tightening torque.
• Effect:
  Misfiring, loss of performance (engine damage).
• Rectification:
  Check engine, ignition and mixture, check spark plug tightening torque. Fit new original BERU brand spark plugs with the correct thermal value.

8 Deposits

• Cause:
  Alloy components, particularly from oil, can form residues that are deposited in the combustion chamber and on the spark plug.
• Effect:
  Can lead to pre-ignition with loss of performance and to engine damage.
• Rectification:
  Check engine adjustments. Fit new BERU brand spark plugs, possibly change oil type.

9 Broken Insulator Nose

• Cause:
  Mechanical damage due to incorrect handling. Initially often only visible as a hairline crack. In extreme cases, deposits between the centre electrode and the nose of the insulator can cause the nose of the insulator to be blown off, particularly if used for an excessive period of time. Knocking engine.
• Effect:
  Misfiring, spark jumps across at points where the fresh mixture may not reach.
• Rectification:
  Fit new original BERU brand spark plugs.

Our Tip for the Hardest of Requirements: BERU Ultra-X

Ground electrode structure provides for improved mixture immersion, the spark position protruding deep into the combustion chamber guarantees reliable ignition. Due to the constant sparking behaviour over the entire life of the plug, the Ultra X provides even more reliable ignition — with optimal engine performance. Ultra X meets the replacement intervals stipulated by automotive manufacturers.

In the figure, an Ultra X, eplaced during servicing: the nose of the insulator is free of deposits, both the ground and centre electrodes show signs of only minor erosion.

Note

The examples shown only apply to 4-stroke engines. Prior to evaluating the appearance of the spark plug, the vehicle should be driven several kilometres/miles in the middle of the power range.