Technical 17 www.aftermarketonline.net APRIL 2026 A routine service, an unexpected misfire: Lessons from a Porsche 911 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 provided the answer. 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 manufacturerspecific 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. The 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. These are often invisible but have noticeable consequences. In this case, upon inspection of the removed spark plug from cylinder four, 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. 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, and covers over 165,000 vehicle combinations; around 97% of all vehicles on Europe’s roads. tinyurl.com/2335y3hx For peace of mind always use a Garage Equipment Association member. GEA accredited engineers work to an industry code of conduct. Your assurance their skills and knowledge have been independently assessed. IS YOUR EQUIPMENT ENGINEER GEA ACCREDITED? Ask your engineer for his accreditation card ! The Upholders of Industry standards since 1945 The Garage Equipment Association www.gea.co.uk GEA ACCREDITED ENGINEER Name Company Discipline Exp Date ID Number XX123456 XX123456 XX123456 XX123456 XX123456
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