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Practical Standalone Tuning: Fuel Configuration and Testing

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Fuel Configuration and Testing

04.22

00:00 Configuring the fuel system means telling the ECU about the size of the injectors fitted as well as how they should be operated.
00:07 The Motec M150 is quite advanced here, and allows the complete characterization data for the injectors to be entered.
00:14 This provides very accurate control of the fuel delivery, but also requires detailed information about the injectors fitted to the engine.
00:22 If we go to the fuel injector sheet in the initial setup workbook, you can see we have a number of settings that need to be configured.
00:29 Firstly, we have minimum volume, reference flow, and reference pressure for the injectors.
00:35 The critical part though is the linearization table which is a 4D table that defines injector flow based on pulse width, fuel pressure, and battery voltage.
00:46 From these parameters the ECU knows exactly what pulse width is required to provide the required fuel flow.
00:53 The way the M150 deals with the injector setup is quite advanced and still not too common.
00:58 So we're going to look at the settings in a more conventional Motec Hundred Series ECU too.
01:04 In the Hundred Series the injector operation mode is defined partially by the trigger mode the engine uses.
01:10 Where possible we want to use sequential injection where each injector is operated separately, and this requires that the ECU has a sync input to tell it where in the engine cycle it is.
01:22 When configuring the fuel system, we start by setting the type of injector that we are using either pick and hold, or saturated drive.
01:30 Motec defined this with the injector current and peak and hold ratio.
01:35 Be aware that some ECUs are not compatible with low impedance peak and hold injectors without adding a ballast resistor.
01:43 The next setting we have to adjust is the injector dead time table.
01:47 This is a simplified version of the injector linearization table in the M150.
01:52 Motec referred to this table as injector battery compensation while it's also known as injector dead time, or injector latency in other ECUs.
02:02 This table required some detailed injector data so you can fill it in properly.
02:06 Fortunately, this data is available with most quality aftermarket injectors.
02:11 If your ECU uses a millisecond-based main fuel table, you'll need to set a base injector pulse width which basically calibrates the fuel output.
02:20 This isn't necessary with the M150 since it uses a proper volumetric efficiency-based fuel delivery model.
02:27 In Motec's Hundred Series ECU, this base pulse width is referred to as injector scaling.
02:33 The number here refers to the injector pulse width supplied with a number of 100 in the fuel table at 100 kPa manifold pressure before any compensations are applied.
02:45 We want to select this number to give us good resolution in the main fuel table.
02:49 The correct number will depend on the size of the injectors, the fuel pressure, and how much power we expect to make.
02:56 While you can calculate the likely pulse width using an estimate of engine VE, and the calculations we learned in the EFI Fundamentals course.
03:04 It really isn't necessary since we can tweak this later as we will see.
03:09 I will normally start with a master pulse width of around 10 to 12, and adjust this later once we have the engine running.
03:16 Once we have the fuel configuration complete, we can test the injector outputs.
03:21 Most ECUs provide a test output mode which can be used to drive an output and test it's working correctly.
03:29 The M150 has a special test mode where the test RPM can be set, and each output can be tested as if it was operating at the test RPM.
03:38 We can use this to test each output individually.
03:41 We're going to start by selecting a test RPM of 2000, and we can use the test output to select each injector output.
03:50 When you do this you want to make sure that the fuel pump is not operating as otherwise you'll end up injecting fuel into the engine.
03:57 While you're testing the injectors, you should be able to audibly hear the injector operating, and you can isolate and confirm the correct injector is operating.
04:07 You can confirm this by unplugging the injector.
04:10 This is a great way to confirm the injectors have been wired in the correct firing order.