R9/22 from the 300d: The Grandfather of INDIRECT gasoline fuel injection
Direct injection has been used in diesel motors since its inception in 1925 and was first used in a mass-produced car in the W138 260D, but direct injection for gasoline vehicles wasn't introduced to the public until the release of the W198 300SL Gullwing. Despite the innovation the 300SL fuel injection pumps were a bit of an evolutionary dead end as the mechanical technology of the time proved imprecise and any wear would result in less than ideal operation and engine performance. It would end up being the pump from a rarer and more luxurious family member that would set the stage for the future of gasoline fuel injection.
Setting the Stage for the Future
As the end of production neared for the W198 development was underway for its successor, the W113, but the persistent problems and high cost of the direct injection system would be detrimental for a higher-volume follow-up. Mercedes-Benz took the opportunity to explore indirect fuel injection with the W189 300d, the last of the so-called "Adenauers". Despite being used in less than 2,000 vehicles the PES6KL70/320R9/22 would become the basis for all fuel injection pumps that followed.
While still using a pneumatic governor, the R9/22 (pictured here) relied on indirect (or port) gasoline fuel injection which would become the standard for Mercedes-Benz vehicles until the early 2000s. Indirect fuel injection brought many benefits that not only resulted in better running conditions and reliability, but also reduced complexity, cost and maintenance. Acting almost like a fancy carburetor, the R9/22 injected fuel into the intake manifold rather than directly into the combustion chamber, requiring less pressure and precision which prevented fuel dilution and rich cold-start problems that plagued the 300SL, issues that persist with the vehicles into the modern day.
In following models many changes were made as development progressed. Diaphragms and vacuums would be replaced with fly wheels and space cams to better measure and deliver fuel. Lower pressure requirements meant components like the fuel feed pump could be entirely removed, while tapping into the engine's oil supply reduced maintenance needs and allowed the removal of the dipstick. They also reduced the pump's weight, increased the viewing window and made various other design changes throughout the years.
PES6KL 70/320 R7
Produced from 1957-1958, this was the first fuel injection pump used for the W189 300d, reverting to indirect fuel injection which would become the go-to fuel delivery method for the brand until electric fuel injection in the early 2000s.
PES6KL 70/320 R9/22
Produced from 1959-1962 this was the last pneumatic governor fuel injection pump used by Mercedes-Benz. Using indirect fuel injection, this pump was the basis for all models moving forward.
PES6KL 70/120 R11
The R11 was produced for the W113 230SL and introduced some major improvements over the R9/22. Fuel/air mixture was more accurately controlled with a flywheel and space cam, the fuel feed pump was removed, and a starting solenoid was added.