The R9/22: Building a Foundation for the Future
While the W198 300SL gets all the attention and is credited with bringing direct fuel injection to gasoline vehicles, those fuel injection pumps were essentially a dead end as the mechanical technology of the time just wasn't precise enough to deal with the needs of a daily driver. Though used in less than 2,000 vehicles, it was the rarer PES6KL 70/320 R9/22 from the W189 300d Adenauers reverting to indirect fuel injection that really set the foundation for the future of fuel injection pumps when it comes to Mercedes-Benz vehicles of the 60s and 70s.
Direct fuel injection in gasoline vehicles might have been a good option for racing but it was less than ideal for getting around town. Rich running issues plagued the production vehicles and oil dilution was a common problem that lead to a variety of maintenance needs over time. A race car can handle fuel dumping into the engine as they are regularly being pushed to their limits, but daily drivers spend a lot more time driving slowly, or idling at a stand still, and direct fuel injection was too problematic to put in a mass-produced vehicle. The 300SL made a huge cultural and technological impact, but the effect on the brand's bottom line left something to be desired. Despite its fame, the 300SL was expensive to produce and had a very limited market. The W121 190SL eased some of that pain, but failed in comparison when it came to performance. Mercedes-Benz needed to increase the production numbers of the follow-up to the W198 300SL and W121 190SL and they needed a more reliable way to feed gasoline to the motor.
Mercedes-Benz bridged the gap, so to speak, and used their flagship model, the W189 300d, as a testing ground of sorts for fuel injection pumps that would follow. While other Adenauers used carburetors, Mercedes-Benz used the low-volume 300d to develop the indirect fuel injection pumps known as the R7 and R9/22. While more primitive, indirect fuel injection using a fuel injection pump could more accurately measure the gasoline needed than carburetors, improving performance, efficiency, and reliability and it didn't run into the same oil dilution issues as direct injection.
While updates and evolution continued throughout the next decade, with major changes including removal of the fuel feed pump and a switch to fly-weights and space cams in lieu of the pneumatic governor, the R9/22 set the stage for the most common Mercedes-Benz mechanical fuel injection pumps and deserves its spot in history for establishing the way forward despite the fame of its "revolutionary" brethren. Learn more about the fuel injection pumps of the W189 and how they paved the way for the future over on our dedicated W189 pump page.
Check out more on the R11, R18, and R20 series that followed and learn about 300SL pumps by clicking those links.
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