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EFI Tuning Fundamentals: Trigger Inputs

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Trigger Inputs

05.58

00:00 - As technology has advanced, the ability of the ECU and the number of tasks it's in charge of handling has also increased.
00:07 The main job of the ECU is obviously to manage fuel and spark delivery for the engine but with the processing power available in modern units, this is just scratching the surface of their potential.
00:19 It's not uncommon these days to have the ECU control cam position, electronic drive by wire throttle bodies, boost pressure, gear box shift functions, variable length intake runners and traction control.
00:32 Essentially, the capability of the ECU and what it can achieve is only limited by the imagination of the engineers and the tuner.
00:40 In this section, we're gong to discuss some of the more common inputs and outputs that you'd expect to see in a typical EFI installation and look at what each component does.
00:50 The most important sensor in any EFI system is the engine speed sensor, often referred to as the reference sensor or just ref for short.
01:01 This is the sensor responsible for telling the ECU how fast the engine is turning and often the sensor will also give the ECU some information about engine position.
01:11 This is critical information for the ECU since it uses this as the basis for all its fuel and ignition calculations.
01:19 If this information isn't accurate, then the ECU can't do its job properly.
01:24 There are a huge variety of sensor and trigger wheel designs used by different manufacturers to provide this information.
01:31 The basic principle, however, remains that the ECU must receive a signal that varies in relation to engine speed.
01:39 While we can run the engine with just an engine speed sensor, it would also be nice if the ECU also knew exactly where abouts it was in the engine cycle too.
01:49 This information can be provided by a synchronisation sensor, or sync sensor, for short.
01:55 This sensor may also be referred to as an engine position sensor.
02:00 The sync sensor works in a similar way to the reference sensor, but it tells the ECU where abouts in the engine cycle it is, or to put it another way, which cylinder is firing at any particular time.
02:12 Since you'll remember the engine completes two revolutions for each engine cycle, the sync sensor needs to receive a signal once every two engine revolutions.
02:23 To achieve this, it's normally driven off the camshaft, since the camshaft operates at half engine speed.
02:29 A sync sensor is essential, if you want to run sequential fuel injection or a coil on plug ignition system.
02:36 It's quite common for the ECU to receive some information on engine position via the reference sensor and this may be done with what's known as a missing tooth trigger disc.
02:46 These discs are machined with an even number of teeth with some of those teeth then cut off to create a gap.
02:53 There are a variety of missing tooth trigger wheels designs, but two of the most common designs are the 36 minus 2 and 60 minus 2 discs.
03:02 These trigger discs consist of 36 evenly spaced teeth with two cut off, or 60 evenly spaced teeth with two cut off respectively.
03:11 The missing tooth style of trigger disc provides the ECU with information about where the engine is relative to TDC on number one cylinder.
03:20 But if the trigger disc is located on the crankshaft then the ECU still doesn't know which stroke the engine is on since it will see the missing teeth every engine revolution.
03:31 Remembering, there are two revolutions per engine cycle.
03:35 What this means is that the engine may be on the intake stroke or the power stroke, but the ECU can't tell the difference.
03:42 To get a complete picture of exactly where the engine is in the cycle a synchronisation sensor is still required.
03:49 Some trigger inputs are better than others, and in my career many of the problems I've seen and experienced have been the result of problems with these components.
03:59 A great example of this is Nissan's 360 degree optical pick-up used on many of their engines including the popular SR20 and RB.
04:09 In this application, the trigger system is driven from a camshaft and consists of 360 slots for the engine speed input.
04:18 This is a huge amount of information for the ECU to process and it also provides very little room for error.
04:25 While the trigger system may work adequately on a stock engine, the valve train harmonics created with a more aggressive set of aftermarket cams can play havoc with this style of sensor, resulting in the ECU losing track of engine speed and position.
04:40 This happens because at certain points in the rev range, the valve train may reach a resonant frequency and at this point the optical sensor tends to oscillate and this can lead to the ECU missing some of the slots.
04:53 When the ECU loses track of the engine RPM or engine position, it will affect all of the calculations the ECU is performing and this can result in the incorrect ignition timing being delivered as well as the wrong amount of fuel being injected.
05:06 In instances like this, a different trigger system may need to be fitted to the engine.
05:13 The key points to take away from this module are that there are a huge variety of sensor and trigger wheel designs out there designed to measure the engine speed and they're usually referred to as a reference sensor or ref for short.
05:26 The synchronisation sensor or sync sensor for short works in much the same way but it tells the ECU where in the engine cycle it is and this is usually run off the camshaft.