Interelectrode gap on spark plug (Audi A4 B6)

Along with the appropriate heat rating, there must be a certain distance between the spark plug electrodes. This distance in most engines is between 0.9 and 1.1 millimeters, but it may change during the operation of the spark plugs.

This is due to the high voltage during the spark jump, which is accompanied by small metal particles breaking off from the electrodes. At the same time, the spark gap increases, and this requires more ignition voltage. If the gap becomes too large, misfires occur, and the engine may not start.
To measure the distance between the side 1 and middle 2 electrodes, you will need a feeler gauge. This distance should be 1.0 mm with a tolerance of ±0.1 mm. In multi-electrode spark plugs, which are increasingly used, the gap between the electrodes cannot be adjusted. These spark plugs are very stable, but if the measured value is outside the tolerance, the spark plugs must be replaced.