Working with Direct Injection (DI)
Direct Injection (DI) is a method of fuel delivery in modern internal combustion engines. As the name suggests, the fuel is injected directly into the combustion chamber, rather than traditional systems where fuel is mixed with air in the inlet, or intake manifold, before entering the combustion chamber.
The advantages of DI are significant, including a greater degree of control over the timing and amount of fuel delivered, improved fuel efficiency and consumption, reduced emissions, and increased power output from delivering higher compression ratios without knocking.
These benefits usually come at a cost. DI systems can be more expensive to implement, requiring higher pressure fuel pumps, specialized injectors and many more hours work.
The additional requirements for DI
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.
DI engines have many hardware characteristics that are difficult to accurately determine without sophisticated DI-specific test equipment. As DI is not yet widely used in the performance aftermarket, there’s limited documented information, even for common DI hardware.
Initial Set-up
For initial set up, many parts of the system need accurate characterisation. Most of this is complicated and requires specialist equipment. The engine must be fitted with a degree wheel to mechanically measure the pump lobe profile (this may require engine removal and machining of adapter parts).
If you’re not using matching OEM driver boxes then the electrical signals for the pump and injectors need to be reverse engineered so an aftermarket DI box can duplicate it. This would usually require an oscilloscope and current probe connected to another car with a similar/same engine running a factory ECU, and this needs to be done under a range of different operating conditions.
The injectors then need to be characterized and all the relevant fuel and air related sensors need to be calibrated accurately. This initial setup step could take several days to a week, depending on factors like engine accessibility, the need for engine removal, and access to another engine running the same factory ECU for scoping
High-pressure fuel pump control
Once the initial setup is complete, you’ll need to tune the high pressure fuel pump control related systems, to ensure stable fuel pressure across all operating conditions. This is complex due to the many variables affecting control, camshaft position, pump dead time, battery voltage. Fuel pressure isn’t constant in DI engines, and needs to be able to change very quickly with load. This step could also take several days to a week, depending on the quality of your work in the initial set up.
‘Normal fuel tuning’
After achieving consistent fuel pressure control, you can proceed to ‘normal fuel tuning’.
Port injected engines generally have fixed fuel pressure (or a very small range of pressure), and fixed injector timing that has little consequence even if not fixed. In other words, you only need to optimize the amount of fuel injected under different RPM & load conditions to get a port injected engine running reasonably well.
With DI, fuel pressure will vary by a factor of about 25 from cranking to WOT, and this means a small error at low pressure suddenly becomes a big error when you increase the pressure 25 times. Injector timing is critical as you only have a short window of time to inject into and which varies with RPM/Load.
You will need to optimize the fuel injection in the same way as port at all RPM and Load conditions, and you also have target pressure and injector timing adding a big influence which needs to be optimised at the same time. This could triple the tuning time required for general fuel tuning. Cold and hot start tuning is also more difficult on DI engines and will require more time
If you are comfortable with the above, you can find more information about the G5 Voodoo Pro on this website including how to purchase. If you would like to discuss further, please contact our 24/6 tech support team.
