Maintaining the fuel system in a classic Mercedes-Benz 220D is crucial for optimal performance and longevity. Like many owners of these robust diesel vehicles, addressing issues related to fuel delivery often becomes a necessary part of ownership. Recently, while working on a 1974 240D (equipped with the 616.916 engine, similar in many respects to the 220D), a common issue surfaced: low fuel pressure. This led to the decision to rebuild the lift pump, a vital component in ensuring the engine receives the fuel it needs. This article details the experience of rebuilding the lift pump and highlights some important considerations for Mercedes-Benz 220D owners undertaking similar maintenance.
Understanding the Mercedes-Benz Diesel Lift Pump
The lift pump, sometimes referred to as a fuel feed pump, plays a critical role in drawing fuel from the tank and supplying it to the injection pump. In older Mercedes-Benz 220D models and similar vehicles from that era, two main types of lift pumps are encountered: early style pneumatic governed IP lift pumps and later, non-pneumatic versions. The key difference lies in their internal mechanisms and the components included in their respective rebuild kits.
The initial plan was a straightforward rebuild using a kit sourced from Mercedes-Benz, based on previous experiences and online information. However, upon receiving and opening the kit, a discrepancy was immediately apparent.
The Lift Pump Rebuild Kit: Unexpected Contents
The expectation, based on online resources and typical kits for later non-pneumatic IP lift pumps (like the Bosch DGK301 kit), was to find a comprehensive set of components. These usually include gaskets, copper rings, O-rings, and valve assemblies. However, the kit received for this early style pneumatic governed IP lift pump contained only two O-rings and two valve assemblies, along with anti-corrosion paper. Notably absent were the copper rings and the crucial mounting gasket.
This difference is significant because it highlights the variation in rebuild kits depending on the specific type of lift pump installed in your Mercedes-Benz 220D or similar model. It’s essential to correctly identify the type of pump before ordering a rebuild kit to avoid missing parts and ensure a successful repair.
This image shows a Bosch DGK301 rebuild kit, typically associated with later, non-pneumatic Mercedes-Benz diesel lift pumps, highlighting the expected components like copper rings and gaskets that were missing from the kit received for the early style pneumatic pump.
This image represents the actual contents of the rebuild kit received, which only included O-rings and valve assemblies, lacking the copper rings and mounting gasket, indicating a kit for an early style pneumatic governed IP lift pump.
Diagnosing Low Fuel Pressure in a Mercedes-Benz 220D
The decision to rebuild the lift pump wasn’t arbitrary. It stemmed from a diagnosis of low fuel pressure and suction, measured using a dealer service lift pump tester and following the factory service manual (FSM) procedures. Low fuel pressure can manifest in various performance issues in a Mercedes-Benz 220D, including reduced power, sluggish acceleration, and difficulty starting.
In this particular case, the 1974 240D felt noticeably less powerful compared to a similar, rebuilt engine in a 1973 model. While rear differential ratios can play a role, the lift pump test indicated inadequate performance, suggesting it was a contributing factor to the power deficit.
The Rebuild Process and Expected Outcomes
Despite the unexpected contents of the rebuild kit, the process of replacing the O-rings and valve assemblies was carried out. The hope is that this refresh will improve the lift pump’s performance and contribute to resolving the low power issue. Furthermore, the plan includes making minor adjustments to the camshaft and injection pump (IP) timing to further optimize engine performance.
This experience underscores the importance of thorough diagnosis when addressing performance issues in a Mercedes-Benz 220D. While a lift pump rebuild can be a beneficial maintenance step, especially in older vehicles, it’s crucial to ensure you have the correct parts and understand the specific type of components your vehicle requires. For owners of Mercedes-Benz 220D models experiencing similar symptoms, testing the lift pump pressure and considering a rebuild with the appropriate kit is a worthwhile step in restoring optimal engine performance.
