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.

Click on images to enlarge Brucato Pro Control Unit.  Note Steamwheel interface.

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.

Click on image to enlarge PCU Internal Potentiometer Layout

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%.

Click on images to enlarge Left: PCU with cover removed. Middle: Internal bi-directional serial interface. Right: PCU adjustment potentiometers.

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.

Page Three: Fuel Mixture Theory, and Fine Tuning the PCU