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EFI Tuning Fundamentals: Injector Drives

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Injector Drives

03.35

00:00 - The other main job the ECU is in charge of is delivering fuel to the engine.
00:04 The ECU does this with an injector driver that controls the voltage supply to the fuel injector.
00:10 Like the ignition drives, the number of injector drives available will depend on the ECU, and this is another aspect you need to consider before purchasing and ECU.
00:20 The number of injector drives will dictate how many injectors the ECU can operate and how they can be controlled.
00:27 There are a few different ways that the ECU can operate the injectors, so let's discuss these methods now.
00:33 The simplest is batch fire, also known as group fire.
00:36 This is where all the injectors are pulsed together at the same time.
00:41 With batch fire, the injection event can't be timed to happen at a particular point in the engine cycle.
00:47 Some injectors may inject while the intake valve's open, while others will inject against a closed valve.
00:53 With batch fire injection, the ECU doesn't need to know where the engine is in the engine cycle.
00:59 This is a nice, easy way of operating the injectors, but it does have some drawbacks.
01:04 Since we can't control specifically when the fuel's injected relative to the intake stroke, we may find discrepancies in the mixture preparation on different cylinders dependent on if the fuel was injected against an open valve or a closed valve.
01:18 This can affect the air fuel ratio cylinder to cylinder and is most apparent at idle and low RPM or load.
01:26 This can make it difficult to achieve good idle quality, particularly with engines that have been fitted with large injectors.
01:33 A better approach is to use sequential injection where each injector is operated individually.
01:39 This lets the ECU time the injection event on each cylinder precisely, ensuring consistent mixture preparation and an even air fuel ratio across all of cylinders.
01:50 Sequential injection requires a sync pulse so that the ECU knows where the engine is in the engine cycle or in other words, which cylinder is on the intake stroke at any time.
02:00 We also need an ECU that has enough injector drives available to suit our engine.
02:06 This means if we want to run sequential injection on an eight-cylinder engine, we need an ECU with at least eight injector drives.
02:13 The last option we'll look at for controlling the injectors is staged injection.
02:19 This is used on some specialised race engines and rotary engines that have very large fuel requirements.
02:25 If these engines were only fitted with a singly injector per cylinder, or rotor, the injector would need to be extremely large to supply enough fuel to cope with the required fuel flow at high RPM and load.
02:37 The problem is that these large injectors may not offer great control at the very small pulse widths we're likely to need at idle and cruise.
02:45 This can make it impossible to achieve a stable and consistent air fuel ratio under these conditions.
02:51 The alternative is to fit the engine with two injectors per cylinder.
02:55 Here, a small injector is normally used at idle and cruise where the engine doesn't need much fuel supply.
03:02 At higher power levels, a larger injector also begins to operate to add the required fuel in order to keep the air fuel ratio under control.
03:10 This allows the engine to make very high power, yet retain great drivability and idle quality.
03:17 So to sum up, the three techniques available for operating the injectors are batch fire, sequential, and staged injection.