Spiel

April 2022

Issue link: https://digital.nexsitepublishing.com/i/1466236

Contents of this Issue

Navigation

Page 37 of 53

ALLAN CALDWELL Technical Editor PORSCHE FUEL DELIVERY AFTER STORAGE A s discussed last month, the two most critical issues for getting an older Porsche running reliably again after three years of limited driving and storage are ignition and fuel supply. The fuel supply issue can often be the most critical because of the many design changes and upgrades that were incorporated from the first fuel injection systems in 1969 through the production of the air-cooled engines and addition of the liquid-cooled engines. Figure 1 shows an overall summary of the fuel delivery and injection systems that were used after 1970. Figure 2 shows some of the major changes in the delivery systems that occurred as the injection systems were adapted to the later engine and fuel transfer equipment requirements. After our COVID-19 storage period, it is worthwhile for the owner to review how the fuel transfer system works on their car and where the critical components are located between the tank and the engine. The purpose of this technical note is to review some of the major changes in Porsche fuel delivery systems from the beginning of fuel injection until the late 1990s when all the cars were equipped with the refined On Board Diagnostic (OBD) systems that can help identify fuel system faults. FUEL DELIVERY SYSTEMS The delivery system includes the fuel tank storage, fuel delivery pump(s), fuel filter system, and fuel transfer lines along with pressure check valves to allow proper fuel pick up, pressurization, and transport into the system. Sketches of the three major types of fuel delivery systems used for the 911 electronic injection engines are shown in Figure 1. A more detailed description of the early fuel delivery systems prior to 1998 is provided in References 1 and 2. Because of the extensive 911 use of mechanical injection from 1969 through 1974 and Continuous Injection System (CIS) from 1974 to 1983, the 911 series did not get electronic injection until 1984. The earliest 911 electronic systems, from 1984-1994, utilized the Bosch Digital Motor Electronics (DME) systems but still retained many of the same sensor types as previously used in the earlier electrical analog systems such as the L Jetronic. After 1984, the systems logically divide up into three groups: 1984-1997 with manifold injectors, moderate fuel pressures, and various pump locations; 1998-2008 with fuel pumps relocated into fuel tanks; and from 2009 on with use of high-pressure, direct fuel injection into the cylinder. In addition, from 2002 on, Porsche moved the pressure regulators into the fuel tank with the pump and discontinued the use of the fuel return lines that had been used since the introduction of the continuously running rotor cell fuel pumps in the 1969/1970 models. Some of our past reviews, such as References 1 and 2, have summarized owner issues that can require solutions to keep the early systems working reliably. Owners' operational problems can involve the fuel delivery system from the tank to the injection system as well as the injection system itself. The DME fuel injection systems can develop problems with their power supply, sensors, and electronic equipment that can affect engine operation. OBD systems on the newer models help identify problem sources when something isn't working 38 Spiel – April 2022 APRIL TECH NOTES

Articles in this issue

Archives of this issue

view archives of Spiel - April 2022