THE TRANSITION FROM DIESEL TO GAS
Fuel injection was used for diesel vehicles since its invention in 1925 but found a wider audience starting around 1935 when Mercedes-Benz introduced the OM138 engine and the W138, one of the first production vehicles to use a diesel engine.
In the 1950s Mercedes-Benz began experimenting with gasoline fuel injection and in 1953 replaced the carburetors with fuel injection in their famed W198 300SL "Gullwing" for the racing season. This change was carried over to the final model of the flagship "Adenauers", the W189 300d in 1957, with the model pictured here.
The R9/22 is referred to as a "pneumatic governor pump" meaning it uses a diaphragm unit and the venturi effect to create a vacuum based on air flow velocity which, in combination with gasoline injection, controls engine speed.
Pneumatic Governor Pumps
The Diaphragm
While there are countless differences, the main thing that separates these pumps from later models is the pneumatic governor and, more specifically, the diaphragm it uses to create a vacuum which controls the air/fuel mixture.
Pictured are two examples of diaphragms used in the R9/22 and R3 pumps. Main differences seen are the materials. The R9/22 uses a natural leather while the R3 uses a petroleum-based rubber.
​
Also pictured are the springs that control the diaphragm and allow it to adjust the fuel mixture. As you can imagine, this was not the most efficient method for controlling air/fuel mixtures and later pumps quickly replaced the diaphragms with fly weights and space cams.
Lastly we have an R7 pneumatic governor pump with a third material used for the diaphragm. The R7 also uses natural leather but with a stained white finish. Other than appearance, it's unclear if this material provided a specific benefit or was used for other reasons such as ease of availability.
Check out more on the R9/22 below
Here we have a picture showing the linkages within the governor which are connected to the diaphragm. While exact layouts differ from model to model, this general setup controlled and adjusted the air/fuel mixture during operation. This system was not ideal for minute adjustments and any leak in the vacuum circuit moves the mixture towards rich fuel delivery. As such many vehicles using these pumps experience imperfect operation and only a full restoration of the fuel injection pump can correct these running issues.
Pneumatic Pumps
Bosch R7
PRODUCED FROM 1957-1958
MODEL: W189 300d "ADENAUER"
This R7 comes from a later years of the W189, made specifically for the 300d Adenauer, making it one of the more sought-after and harder to find models of fuel injection pumps. Similar examples have auctioned for up to $30K dollars, so it makes sense to do everything possible to bring one back to life.
The R7, being a later model of pneumatic governor pumps, features the bleached leather diaphragm visible on our pneumatic governor page, as well as various upgrades that increased efficiency and dependability.
At the bottom of the page you can see how we go about testing this fuel injection pump to ensure the calibration is
on target and will produce ideal performance.
(Video in progress)
On the Bench
Pneumatic Pumps
Bosch R9/22
PRODUCED FROM 1959-1962
MODEL: W189 300d "ADENAUER"
This R9/22 comes from a later years of the W189, made specifically for the 300d Adenauer. Like the R7, this is a relatively rare pump and demands high numbers at auction when available.
The R9/22 features the traditional leather diaphragm visible on our pneumatic governor page, as well as various upgrades that increased efficiency and dependability.
These images are from before the restoration showing what the pump looked like when it came in. Here you can see the grime that can build up on the exterior of the pump.
Take a look through the gallery below and check back in for testing videos and updated photos as we continue the process of restoring this pump.
