For owners of the classic 280sl Benz, maintaining its timeless appeal often involves navigating the challenges of older technology. One area where modernization can significantly enhance performance and reliability is the fuel system. This guide details the process of upgrading from the original Bosch K-Jetronic system to a modern Electronic Fuel Injection (EFI) system, specifically using MegaSquirt. While this write-up focuses on the 280SL Benz, the principles can be applied to other vehicles utilizing similar Bosch fuel injection systems, including the older D-Jetronic.
This isn’t a step-by-step manual for every nut and bolt, as much of the installation is straightforward and visually self-explanatory. Instead, this article aims to provide a comprehensive overview of the EFI conversion, highlight key considerations, and empower you to undertake this rewarding DIY project. Remember, successfully installing a MegaSquirt EFI system requires research and understanding of your vehicle and engine.
Think of this upgrade as the best enhancement you can make to breathe new life into your classic 280SL Benz.
It’s worth noting that some parts of this guide are inspired by and adapted from existing resources within the MegaSquirt community, where complex concepts are often explained with great clarity.
Let’s demystify some common terms before diving in:
EFI (Electronic Fuel Injection): A modern system controlling fuel delivery electronically for improved efficiency and performance.
MS (MegaSquirt): An open-source, customizable EFI system, popular within the DIY automotive community.
ECU (Electronic Control Unit): The “brain” of the EFI system, processing sensor data to control fuel and ignition.
AFR (Air Fuel Ratio): The ratio of air to fuel in the engine’s mixture. 14.7:1 is Stoichiometric (ideal for emissions), while 12.5-13:1 is typically best for power.
TPS (Throttle Position Sensor): Measures the throttle valve angle, indicating driver demand.
CLT (Coolant Temperature Sensor): Monitors engine coolant temperature for ECU adjustments.
IAT (Intake Air Temperature Sensor): Measures intake air temperature, affecting air density and fuel needs.
MAP (Manifold Absolute Pressure Sensor): Measures pressure in the intake manifold, crucial for fuel calculations based on engine load.
VR Sensor (Variable Reluctor Sensor): A sensor used to detect crankshaft position for timing and RPM signals.
FP (Fuel Pump): Pumps fuel from the tank to the engine.
FPR (Fuel Pressure Regulator): Maintains consistent fuel pressure for the injectors.
Trigger Wheel: A toothed wheel on the crankshaft pulley used with a VR sensor to provide precise engine position data.
Understanding MegaSquirt
MegaSquirt stands out as a versatile aftermarket EFI controller designed for spark-ignition engines. Developed by Bruce Bowling and Al Grippo, it’s a complete system encompassing both hardware and software. Its open-source nature (software modification allowed for Bowling and Grippo hardware) and readily available schematics make it a favorite among DIY enthusiasts. While primarily focused on fuel and ignition control, MegaSquirt offers configurable outputs for various auxiliary functions. Keep in mind that MegaSquirt is geared towards the DIY market, typically requiring assembly and tuning by the user.
The MegaSquirt ECU relies on inputs from various sensors to precisely control fuel injectors. These sensors include:
- Throttle Position Sensor (TPS)
- Oxygen Sensor (O2 or Wideband EGO sensor)
- Manifold Air Pressure (MAP) sensor
- Crank Position Sensor (or distributor tach signal)
- Intake Air Temperature (IAT) sensor
- Coolant Temperature (CLT) sensor
Often, GM-style sensors are used, but MegaSquirt can be calibrated to work with other sensor types like Bosch or Ford.
MegaSquirt Versions for Your 280SL Benz
Different MegaSquirt ECU versions (MS1, MS2, MS3) have emerged over time, offering increased processing power and features. MS2 is a popular, well-supported option, while MS3 represents the latest generation, gaining traction for its advanced capabilities and growing community support. For 280SL Benz owners, the MS2 with “extra code” software (version 3.11 or later) is often ideal, providing the necessary features and configurability for these engines.
Why Convert Your 280SL Benz to EFI?
The original Bosch K-Jetronic system in the 280SL Benz, while reliable for its time, can feel dated compared to modern EFI. Even on well-maintained K-Jet systems, a slight “lag” in engine response can be noticeable. The motivation for upgrading often stems from a desire for a more responsive and modern engine character. Furthermore, repairing or sourcing parts for aging K-Jet systems can be costly and challenging.
Before undertaking the EFI conversion, this particular 280SL Benz (a 1985 model) was already equipped with a lambda sensor and catalytic converter. Prior to the MegaSquirt installation, the owner upgraded the narrowband oxygen sensor to a wideband sensor and installed an Air/Fuel Ratio (AFR) gauge. Monitoring the AFR with the K-Jet system revealed it performed admirably, maintaining appropriate fuel mixtures for cruising and acceleration.
The key advantages of EFI conversion for a 280SL Benz include:
- Improved Engine Responsiveness: Modern EFI delivers fuel more precisely, eliminating the “lag” sometimes felt with older mechanical systems.
- Enhanced Tuning Capability: MegaSquirt allows for fine-tuning of fuel and ignition maps for optimal performance and efficiency across various driving conditions.
- Increased Reliability and Simplicity: Replacing aging K-Jet components with modern EFI eliminates potential failure points associated with the older system.
- Cost-Effectiveness in the Long Run: While initial investment is required, EFI can be more cost-effective than repeatedly repairing or replacing expensive K-Jet components.
- Maintainability and Upgradability: MegaSquirt is well-supported by a large community, and parts are readily available.
- Reversibility: The conversion can be designed to be reversible, allowing for restoration to the original K-Jet system if desired, as no irreversible modifications to core components are necessary.
Key Components for MegaSquirt EFI Conversion on a 280SL Benz
For a fuel-only EFI conversion on your 280SL Benz, here’s a list of essential components and approximate costs (prices may vary):
- MegaSquirt-II (ver. 3.0) EFI System: $260 – $420 (assembled)
- MegaSquirt Relay Board: $64 – $88 (optional, simplifies wiring)
- Cable for Connecting MS ECU to Relay Board: $75
- GM Coolant Temperature Sensor: $17.75
- GM Intake Air Temperature Sensor: $17.75
- Throttle Position Sensor (TPS): (Volvo 850 TPS is a compatible option) ~$50
- Fuel Rail: (Custom or adapted. Cost varies. Original D-Jet fuel rail might be adaptable) ~$150 (for a 6-cylinder, V8 will need two shorter rails)
- Injectors: (Bosch injectors or Ford Mustang injectors are often compatible. Salvaged injectors can reduce cost)
- Fuel Pressure Regulator (FPR): (Used FPR can be sourced) ~$100
For ignition control in addition to fuel injection, these components are needed:
- 36-1 Trigger Wheel: $25
- Bosch BIP373 coil driver transistors: $8 each (V8 engines need 4 drivers) or “QuadSpark Four Channel Ignition Module” (~$89)
- IGN-6 Six-Tower Coil Pack: $75
- Trigger Sensor: (Mercedes Vito trigger sensor is a possible option) ~$50
A MegaSquirt Simulator w/ Wheel Simulator ($59 – $88) is a valuable tool for testing and troubleshooting the system before installation in the 280SL Benz. A Wideband Oxygen Sensor ($199) is highly recommended for tuning the EFI system, providing real-time AFR data. While it can be removed after tuning, it significantly simplifies the process.
Installation Considerations
The MegaSquirt relay board is optional but highly recommended. It simplifies wiring by providing a central point for connecting sensors, injectors, and the fuel pump, housing relays and fuses, and offering a single grounding point to minimize electrical interference.
MegaSquirt can also control an electric cooling fan (via a relay), allowing for precise temperature-based fan activation and deactivation. It’s also compatible with various types of idle stepper motors for improved idle control.
For ignition upgrades, MegaSquirt provides a 12V square wave tachometer signal output, directly compatible with many aftermarket tachometers, simplifying the connection. If using the relay board, it includes a fuel pump relay, simplifying the fuel pump wiring by utilizing the existing fuel pump relay socket.
A recommended approach is to initially install the MegaSquirt system, wiring everything except the injectors, and verify its functionality before physically removing the K-Jet system. This allows for testing and configuration before committing to the full conversion. Once verified, the K-Jet system can be removed, the new fuel rail and injectors installed, and final connections made.
Choosing MegaSquirt: Community and Support
The MegaSquirt EFI system is a popular choice for DIY conversions due to its strong community support, affordability, and proven reliability. Numerous online forums and resources are dedicated to MegaSquirt, offering invaluable assistance and guidance. Even individuals with limited prior experience in fuel injection have successfully installed and run MegaSquirt systems, highlighting its user-friendliness and the robustness of the community support network.
Conclusion: Elevate Your 280SL Benz with EFI
Upgrading your 280SL Benz to MegaSquirt EFI is a transformative project that brings a classic car into the modern era. It offers tangible benefits in engine responsiveness, tuning flexibility, and long-term reliability. While requiring a DIY approach and some technical understanding, the wealth of community support and readily available components make it an achievable and rewarding endeavor for any 280SL Benz enthusiast seeking to enhance their driving experience. Consider embarking on this journey to unlock the full potential of your classic Mercedes.
