Thinking of Tuning a Direct Injection Engine?

What is direct injection?

Direct Injection (DI) is an advanced method of fuel delivery in modern internal combustion engines, where fuel is injected directly into the combustion chamber. This contrasts with traditional port injection, where fuel mixes with air in the intake manifold before entering the chamber. The benefits of D.I. are numerous, including enhanced control over fuel timing and volume, increased fuel efficiency, reduced emissions, and improved power output due to higher compression ratios without engine knock.

The DI system includes a low-pressure fuel pump, a high-pressure camshaft-driven pump, high-pressure fuel lines, a fuel rail with a pressure sensor, and high-pressure injectors. The ECU and/or DI Driver module controls the injectors based on various engine parameters to optimize combustion. Some vehicles like the Toyota 86 or later model Golf GTIs employ both port and direct injection systems, where the low-pressure pump serves both the high-pressure pump and a separate low-pressure rail for the port injectors.

If you are considering installing and tuning an aftermarket ECU, such as the G5 Voodoo Pro, on a DI engine, it is important to be aware of the additional time and work required compared to a port injection engine. For an unsupported DI engine, there may be several hundred hours of additional work. You must have precise and detailed information about the vehicle’s components and system behavior, this data is referred to as "Characterisation". This can be categorised into two types, Injector data (current profile and flow characteristics) and Fuel Pump information (cam profile, pump control tuning, and target pressures).

As DI is not yet widely used in the performance aftermarket, there is limited documented information, even for common DI hardware.

Before you start, here’s what you need to know:

ECU Compatibility: Ensure your ECU and/or DI Driver can manage your specific type of injectors and high-pressure fuel pump. Systems like Link’s G5 Voodoo Pro ECU and DI Driver-4 module are typically required.
Injector Type: Identify whether your injectors are Solenoid or Piezo, as most aftermarket ECUs cannot control Piezo injectors.
Access to Tools: If you need to create your own characterisations, you will need tools such as an Oscilloscope, Current Probe, Direct-Injector Flow Bench, Dial Gauge, and a Degree Wheel.
Time Commitment: Full characterisation can take one to two weeks, which is feasible if tuning multiple engines but less so for a one-off project.

A full characterisation includes:

Injector Current Profile: Analyze the waveform generated by the injector using an oscilloscope to determine the peak and hold currents and response times.

Injector Flow Characterization: Requires a specialized flow bench to measure injector dead times, and flow rates at various rail pressures.

Fuel Pump Type: Know whether your pump is normally open, normally closed, or uses Pulse Width Modulation (PWM).

Camshaft Profile for the Fuel Pump: Measure the lift and duration of each cam lobe with a dial gauge and degree wheel.

Pump dead time and injector timing: Information on pump dead time and injector timing can usually be obtained from the factory ECU. If unavailable, these must be derived through reverse engineering.

Support from Link Engine Management

At Link Engine Management, we aim to facilitate your tuning process. We offer pre-characterised Injector Current Profiles and Cam Shaft Profiles for some popular engines, saving you the effort of reverse engineering these components yourself, which can significantly cut down on your preparation time. To see if your engine, or components of your DI system are characterised, we have an up-to-date list here.

With all the necessary information in hand, you are set to begin tuning your direct injection vehicle on the dyno. While similar to tuning traditional port injection with modeled fuel, it includes additional considerations like injection timing and fuel rail pressure management.

For more details, and resources, please visit the support section of our website, join our forums, or reach out to our 24/6 Tech Support team. Happy tuning!