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.​ 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 or accurate method for controlling air/fuel mixtures and later pumps quickly replaced the diaphragms with fly weights and space cams.
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.
Lastly we have an R7 pneumatic governor pump with a third option used for the diaphragm. This pump also uses natural leather but later models featured a stained white finish.
Check out more on the R9/22 below
Here you see a vintage illustration showing all the associate parts, gaskets, seals, and piping associated with the PES6KL70/320 R4 & PES6KL70/320 R6 which was produced from 1955-1958 for the W188 300Sc coupes and cabriolets.
This blowout shows how many pieces are involved in the restoration of the pumps, with many of these parts needing inspection, testing, and heavy cleaning if not total replacement. If you're service provider is not disassembling the entire pump, you're likely not getting at the parts that are in the most need of restoration and any work will result in less than ideal performance or a non-running vehicle in the end.
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.
The R7, being a later model of pneumatic governor pumps, features 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.
WATCH US TEST THE R7 HERE
On the Bench
Pneumatic Pumps
Bosch R9/22
PRODUCED FROM 1959-1962
MODEL: W189 300d "ADENAUER"
This R9/22 also comes from a later years of the W189.
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.
TESTING THE R7
