Fuel Setup Questions

I have two fuel rails on my engine running individual throttle bodies. There is a lower rail that positions injectors inside the intake track where they are subject to vacuum pressures, and a second upper rail of shower injectors that are only active at wide open throttle that sit above the throttle butterflies inside the air filter and therefore aren’t subject to much if any vacuum.

So the question I have is if I want the ECU to correct for differential pressure between MAP and the fuel pressure across the injector would I set the lower rail pressure regulator settings to BARO for the reference port pressure, and set the upper rail to MAP for the reference port pressure?

Second question, when use fuel pressure sensor is enabled for the rail under the pressure regulator settings is that just correcting the injector flow rate if the fuel pressure sensor reads different than the reference pressure and assuming a linear relationship between fuel pressure and flow rate? I’m just double checking since with other ECU platforms they required me to make a 1d injector flow rate map with flow rates by pressure, but that doesn’t seem to be an option here.

Also last question, I see there is an option to use imperial units now in the latest software release, but for reference flow unit under injector setup there are only metric units available like mL/min. Will there be on option for the imperial Lb/hr at some point?

Thank you!

The option you are looking for is not currently available. We have to add it, and it will be called “Injectors nozzle side pressure” or something similar. Right now, it’s assumed that injector nozzles see MAP.

The settings you are looking at are for the fuel pressure regulator. You have to tell the ECU whether or not your pressure regulator is compensating for the intake pressure. The regulator’s reference port is usually connected to the vacuum line to the intake plenum. If that’s the case, you must select “With reference port” and “MAP”.

It will work correctly if your secondary injectors are turned on at WOT. That’s because at WOT, MAP, and all injectors will see atmospheric/boost pressure.

The ECU calculates the injector differential pressure, which you can display on the log. It uses the pressure regulator settings to do that. You can calculate this pressure from the base pressure put by hand or from the actual pressure measured by the sensor.

Using the reference flow and pressure, the ECU calculates the injector flow at the current differential pressure. It’s not linear, but yes, it is calculated by the ECU without needing a table.

The problem with injector flow is that you talk about different types of units, which can’t be directly converted. One is volumetric flow, and the other is mass flow. The volumetric flow is universal because it’s the same regardless of the fuel used. If you have injectors that have flow described as mass flow, they also have to tell you with what fuel it was measured. Otherwise, it’s not a complete description.

Since we support different fuels, we have to know the injector’s volumetric flow. We could add an option to input the reference flow as mass flow, but that would also require inputting the fuel density used to measure the flow. That’s not critical, so I don’t think we will be adding that anytime soon.