The Dawn of Fuel Injection
2-PLunger Fuel Injection Pumps
Bosch fuel injection pumps provided increased performance, fuel efficiency, cleaner emissions and more control over the performance of the pump in relation to the engine, allowing minute adjustments to improve overall performance.
While designs advanced at a rapid pace throughout the decade, earlier pumps like the Bosch EP/ZEA2KL R3 (pictured) still marked a vast improvement from carburetors and were used by Mercedes-Benz on their luxury models as early as 1958. The R3 seen here was used in coupes and cabriolet variants of high-end models such as the W128 220SE "Pontons" from 1958-1960, and early W111 220SEbs. The Bosch EP/ZEA2KL is the first iteration of the 2-plunger pump and was first released in 1958.
THE EP/ZEA 2 KL 75
R1, R2, R3, R4, R6, R7
PAGE IS UNDER CONSTRUCTION
Features include black oxide plating, a long control lever in comparison to following models, and an extended corrector assembly. While an improvement on carburetors, a 2-plunger pump, as the name indicates, has only two plungers meaning adjustments apply to half of the injectors. Because of this individual injector performance cannot be controlled as it can in later 6-plunger models. This still allows greater adjustability than a carburetors but left room for improvements.
ZEA PRODUCTION DATES
AND CORRESPONDING MODELS
220SE (W128)
EP/ZEA2KL75 R1
EP/ZEA2KL75 R2
EP/ZEA2KL75 R3
...............2/58-2/59
...............3/59-6/59
..............7/59-12/59
Mechanical
Transmission
}
220SEb (W111)
EP/ZEA2KL75 R4
EP/ZEA2KL75 R6
EP/ZEA2KL75 R7
...............8/59-4/60
...............5/60-12/61
...............8/59-12/61
Mechanical Transmission
}
— Automatic Transmission
The Second Generation
THE EP/ZEB 2 KL 75
R11, R12, R13, R14, R15, R16, R17, R18
The Bosch EP/ZEB2KL75 model was first released in June of 1962 with the R11 and the R13 and featured a number of improvements from the ZEAs. Various mechanical adjustments include modified pressure valves and increased idle performance. Obvious differences include the replacement of black oxide plating with more resilient zinc plating and the reduced size of the corrector assembly extending from the right-upper-portion of the pump on the R3 allowed easier access to the governor, better idle control and more room for install and removal of the pump. Below you see images from the testing of an R14 ZEB, an example of early ZEB pumps.
In the cutouts we have a fully restored R16, a later example of ZEB pumps. Scroll down for more information and images on that model.
R16
ZEB PRODUCTION DATES
AND CORRESPONDING MODELS
220SEb (W111)
EP/ZEB2KL75 R11
EP/ZEB2KL75 R14
................1/62-7/63
.............8/63-10/65
Mechanical Transmission
}
EP/ZEB2KL75 R13
EP/ZEB2KL75 R16
...............1/62-7/63
.............8/63-10/65
Automatic Transmission
}
300SE (W112)
EP/ZEB2KL75 R12
EP/ZEB2KL75 R15
...............4/61-7/63
.............8/63-12/63
Automatic Transmission
}
EP/ZEB2KL75 R17
EP/ZEB2KL75 R18
...............4/61-7/63
...............8/63-12/63
Mechanical Transmission
}
The following images show a fully restored R16 which is a later ZEB model produced after 1963.
This R16 was fully restored in the Black Forest pump shop which included media blasting, ultrasonic cleaning, replating, replacement of all wear items such as seals and gaskets, and was meticulously tested and calibrated using our restored 2-plunger dedicated Bosch EFEP 385A.
Scroll down for a video showing the testing process of this R16.
Bosch EP/ZEB 2 KL 75 R16 Testing and Calibration
2-Plunger Fuel Injection Pumps
Vintage Documents
Original documents for the
Original Fuel Injection pump
In a segment already plagued with little information, 2-plungers have even less knowledge readily available than the 6-plungers like those found in the W198 300SL or W113s. While cutting edge at the time, they were quickly phased out and replaced by 1963, bringing an end to the ZEA and ZEB lines. While they share some similarities in general operation, figuring out the restoration process for the 2-plungers required their own deep dive into vintage materials and trial and error. As the only Bosch authorized service facility to offer rebuilds on all gasoline fuel injection pumps including 2-plungers, we love sharing some of our vintage materials such as the testing manuals seen here.
