• Brucato Pro Control Unit Overview

    For most people reading this article, an introduction to the Electronic Control Unit (ECU) or Electronic Control Module (ECM) of an electronically fuel injected engine is not necessary. Automobiles have been equipped with these units for over twenty years now, in varying levels of sophistication.

    Essentially, the ECU or ECM is an onboard computer system that receives input from various sensors and actuators on and in the engine and delivers the programmed amount of fuel based on this input. As computer technology has increased, so has the ability to more accurately monitor engine operations. The result is more performance from less fuel.

    In most applications, these computer systems fall into two basic categories: "Intelligent" and "Non-Intelligent". ‘Intelligent’ EFI control systems have the ability to receive input from advanced onboard sensors such as Manifold Absolute Pressure sensors, and adjust themselves based on these constantly changing variables. ‘Non-intelligent’ systems differ in that they are usually not equipped to receive and process complex progressive electronic inputs, and therefore, offer less efficiency and performance potential than their more advanced counterparts. Mechanical and early analog fuel injection systems would be examples of non-intelligent systems.

    Although a ‘non-intelligent’ electronic fuel injection system can meter and deliver fuel much more precisely than carburetors, digital fuel injection systems take this much further. Unlike the early analog EFI systems, digital fuel injection systems operate on a more adaptive global model, with the ability to process more data concurrently from a variety of changing parameters.

    The Mercury fuel injection control systems implemented in 2.4 and 2.5-litre V6 outboard engines are somewhat adaptive, although on a very limited scope. They include analog control units and more advanced digital systems. These ECU’s are the basis for the sequential multi-port injection systems designed for these high-performance engines, and are capable of monitoring basic engine functions to a varying degree, depending on the engine model and year.

    Any computer system can be programmed and reprogrammed, however, the ease and level of programmability depends on the sophistication of the computer system’s architecture. For most users, the ECU that the 2.4 and 2.5-litre Mercury engines are factory-equipped with offers the reliability and performance they were designed to deliver in most general applications. Most importantly, the factory ECU offers only basic, limited linear fuel enrichment adjustments. If any further adjustments are required, the ECU can indeed be reprogrammed to remove RPM limiters and alter the fuel mixture, however this involves sending the unit to a specialized facility, which involves cost and downtime. Further, with advanced engine modifications and race applications that demand “on the edge” tuning capability, the importance of easily adjusting the fuel delivery process throughout the entire RPM range becomes clear.


    Brucato PCU System Architecture Explained

    Brucato Machine and Tool introduces the new Brucato Pro Control Unit (PCU), which is a completely user-programmable, “intelligent” digital fuel injection management system. Rather than adding functionality to the existing EFI computer system, the PCU starts on a clean slate by replacing the Mercury ECU entirely. Although the PCU itself is a plug-and-play affair that installs in about fifteen minutes, it offers the user the ability to adjust and program most aspects of the fuel delivery process, utilizing a variety of methods that reach far beyond the programming capabilities of the factory ECU.

    Before we get more in depth, let us look at some of the features of the Pro Control Unit itself:


    • Fuel injectors are fired sequentially in pairs, like the original Mercury ECU. This assures injector firing timed to crank case pressure for accurate fuel delivery.


    • Onboard Manifold Absolute Pressure (M.A.P.) sensor. This allows the PCU to automatically adjust the proper fuel delivery based on engine load (which is determined by intake manifold air pressure) and throttle position. This M.A.P. sensor also performs the function of the Throttle Position Indicator (T.P.I.). On older analog ECU-equipped engines with a T.P.I., and on ProMax or XRI engines that used an external T.P.I., the PCU eliminates the need for the original T.P.I.


    • Expanded Fuel Map. The Brucato PCU utilizes a ‘24 X 16’ fuel map for an accurate calibration of fuel at all levels. What this means is, fuel delivery can be adjusted at 24 RPM levels and 16 different vacuum levels at each RPM point.


    • The PCU automatically compensates for fluctuations in air temperature and battery voltage.


    • The PCU can add or subtract up to 15% fuel delivery to separate pairs of injectors for the ultimate in precise adjustment ability.


    • The PCU can operate up to 13,000 RPM. The rev limiter can be adjusted up to 13,000 RPM in 10-RPM increments.


    • The PCU plugs into the standard Mercury ECU harness on most EFI engines, excluding the 2.5 280-horsepower model and 3-Litre engines. There are plans to adapt the PCU to these engines in the future.


    • The PCU features Acceleration Fuel Compensation, which can be user-adjusted for volume and sensitivity. This feature allows easy adjustment for crisp holeshots.


    • The PCU is capable of interfacing with a Windows-compatible computer via an internal, bi-directional serial connection for advanced-function editing and uploading/downloading fuel curves.


    • Optional Steamwheel module for plus-50% rich to minus-40% lean remote adjustment of the fuel mixture.


    • Optional extension harness to allow remote operation of the PCU for easy adjustments from within the boat while running the engine.



    The PCU is the first such EFI system to simply replace the Mercury ECU, while directly plugging into and using the existing Mercury wiring, including the injector harness. It may be used as a replacement ECU, or more importantly, for fine-tuning the performance of your fuel injected engine.

    Opening the aluminum case of the PCU reveals 31 encoding potentiometers and a serial port. The potentiometers allow manual adjustments of the fuel curve and Acceleration Fuel Compensation. The fuel adjustment pots are labeled from 500-10,500 RPM. The internal encoders, and other components of the PCU are encapsulated in silicone to seal out moisture and protect against continuous vibration.

    The Main encoder knob controls the overall fuel delivery. Essentially, this is a linear adjustment for all of the fuel delivery encoders – all encoder knobs below this are relative to each other, however the Main encoder controls the overall metering of fuel by the PCU.

    Accel-Comp Volume (Acceleration Compensation Volume) allows the user to determine the volume of extra fuel delivered during acceleration, while Accel-Comp Sensitivity adjusts the minimum amount of throttle movement required to activate the Acceleration Compensation function.

    The Part Throttle encoder knob allows a +/- 15% mixture adjustment in the 1800-7000 RPM range, without affecting the Pro Control Unit’s full-throttle fuel calibration.

    The Idle adjustment knob allows a +/- 15% mixture adjustment in the 0-1800 RPM range without affecting full throttle calibration.

    ‘Group 2’ and ‘Group 3’ Adjustments

    Mercury’s electronic fuel injection system is based on a sequential, multi-port design. What this means is that each cylinder is fed by a dedicated injector, but the fuel injectors are grouped and fired sequentially, in pairs. In some applications, it may be desirable to adjust these groups of injectors individually. The PCU is capable managing separate fuel curve adjustments for each pair of injectors. This is where the Group controls are utilized.

    Group 1 controls the injectors at cylinders 1 and 2, Group 2 controls cylinders 3 and 4, and Group 3 controls cylinders 5 and 6. Groups 2 and 3 can be adjusted separately from the Main adjustments +/-15%.

    Although modified engines will ultimately benefit the most from the tuning abilities of the PCU, stock engines will see performance as well as economy improvements. The PCU is simply capable of a finer level of digital EFI implementation than the stock ECU.

    The ‘chemically ideal’ air-fuel mixture, by weight, in which air and gasoline are used, occurs at approximately 14.6 parts air and 1 part fuel. This chemically ideal air/fuel ratio is known as a stoichiometric mixture. Mixtures with more air are identified as lean mixtures, and tend to occur with an air/fuel ratio of greater that 14.7 to 1. A lean mixture results in increased combustion temperatures, which allows for a more complete burn of the fuel. The result is increased power output, however, the risk of severe engine damage looms overhead for those seeking to gain engine performance by venturing into this risky domain. Mixtures with less than 14.6 to 1 ratios are identified as rich burning mixtures. Generally, the rich burn limit for an engine at a normal operating temperature is about 6:1, whereas the lean burn limit is about 22:1 for electronic injection engines, and 18:1 for carbureted engines. The 'ideal mixture' is a model for fuel efficiency - for performance applications, the best mixture will not be the 'chemically ideal' mixture.

    The ideal air/fuel ratio for a particular RPM range in a performance engine is determined by many factors. Some of these factors are compression, ignition timing, octane rating of the fuel, RPM, engine load, and air temperature. Remember, the cooler the incoming air charge, the denser it becomes. The result is that more air molecules can enter the engine at a given time, which has an effect on the fuel mixture. A small alteration to the air/fuel mixture will have a significant impact on engine performance. This is where the PCU’s adjustability plays a central role in precise engine tuning.


    Fine Adjustments Using The PCU

    By allowing precise adjustments to the fuel mixture at all RPM levels, as well as individual pairs of injectors, the engine can be tuned according to many factors, including weather conditions. For example, the advanced user might want to increase the fuel volume (richen the mixture) when operating the boat on an especially cool, dry day to compensate for the increased air entering the engine and potentially avoid a lean condition. The result would be increased performance, although this type of fine adjustment should only be attempted by the experienced user, with the aid of exhaust gas temperature monitoring devices installed.

    Setting up and tuning the Pro Control Unit is a straightforward process, which we will detail in Part Two of this series. The PCU arrives with a baseline fuel curve for your engine already preloaded. It is highly recommended that baseline exhaust temperature readings are recorded before installing the PCU. The tuning process then begins with a +20% rich setting on the Steamwheel or the internal Main encoder, then gradually and carefully leaning the mixture down at the required RPM ranges. The idea is to cover broad RPM ranges at first, and then work your way down to smaller RPM ranges for an accurate tune.

    The Brucato Pro Control unit is a godsend to those that seek to fine-tune their fuel-injected Mercury outboards with uncanny precision. This type of custom programmability has been available to car enthusiast for years, and now it is available to the outboard enthusiast. It is the first such system to offer plug-and-play installation and a level of digital sophistication previously unheard of for the engines it was designed to work with.

    The Pro Control Unit itself costs $1000 US, which is significantly less expensive than replacing a new factory ECU. When you consider the PCU's level of adjustability, quality, and options available, its a real bargain, and an extremely useful tool in the performance boater's arsenal. For pricing on accessories and special pricing on PCU packages with popular accessories, visit the Brucato Machine and Tool website.

    Part Two of this series will focus on installation, setup, complete tuning, and testing the PCU. These tests will be performed on two engines: a modified Mercury 2.5, 260 horsepower (stock rating) EFI with a modified digital ECU, and a mildly modified 2.4, 245 horsepower (stock rating) Bridgeport EFI with a stock analog ECU.
    Comments 2 Comments
    1. Sjefen's Avatar
      Sjefen -
      Is there a part two of this series yet? If it is, where can i find it?

      Thanks
      Christian
    1. Sjefen's Avatar
      Sjefen -
      Any news regarding the Part 2, Greg?

      Thanks
      Christian
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