ALLDATA helps fix Porsche 911 Carrera 4S misfiring
Why would a Porsche 911 Carrera 4S start misfiring on cylinder four following a routine spark plug replacement? ALLDATA and Porsche’s OEM repair data can provide an answer.
Cologne, Germany – 16 March, 2026 – Following a standard spark plug change, a Porsche 911 Carrera 4S (Type 992, 3.0L) returned to the workshop after the driver noticed poor engine performance. The fault code was P0304 – Misfire Cylinder 4. At first glance, it appeared the ‘routine service’ was conducted correctly – but the issue turned out to be an underlying one.
The technician consulted the ALLDATA Info Centre to review all manufacturer-specific installation procedures for the spark plugs. The documentation showed that Porsche provides strict guidelines for this job, especially regarding installation orientation, lubrication and handling of the delicate ceramic insulators.
Solution
According to Porsche specifications, spark plugs need to be installed with the electrode positioned at ‘12 o’clock’. This precise alignment ensures uniform flame front distribution, resulting in clean and efficient engine operation. Additionally, a specified lubricant must be applied to the ceramic insulator to reduce friction during threading and prevent microcracks.
Using the correct tools is equally important; even slight deviations in the threading angle or excessive lateral force can cause fine hairline cracks in the ceramic body – often invisible but with noticeable consequences.
In this case, upon inspection of the removed spark plug from cylinder 4, the technician noticed a barely visible crack in the insulator. This minor damage triggered the misfires and rough engine performance. With a new, correctly installed spark plug, the issue was resolved. The six-cylinder engine ran smoothly and evenly once again.
Simple tasks require maximum precision
This example illustrates that even simple maintenance tasks today require maximum precision, care and accurate technical information. Small deviations can lead to consequences – from minor misfires to catastrophic engine damage.
With access to original data and practical support, ALLDATA helps workshops avoid mistakes, identify root causes and carry out repairs confidently.
With data from 44 VMs, over 106 million technical articles and more than nine-and-a-half million wiring diagrams and drawings, ALLDATA Repair covers over 165,000 vehicle combinations – that's around 97% of all vehicles on Europe's roads.