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Practical Wiring - Club Level: Sensor Design

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Sensor Design

07.20

00:00 - With the power supply and grounding schemes of our wiring harness designed, we can move on to the sensor, actuator and network communications design.
00:07 These sections are typically much more straightforward and consist of us identifying the remaining EFI components, how we're going to interface to them, and any particular wiring requirements that they might have.
00:18 The first sensors I consider are the engine position and speed sensors.
00:22 If they're a digital signal type, either optical or hall effect, they will require either power supply and power ground or sensor supply and sensor ground.
00:31 Most OEM sensors require a power supply and a power ground, with many aftermarket triggering systems using threaded hall effect sensors which need the lower voltage sensor supply and sensor ground.
00:42 If your sensor is a variable reluctor type, it will not require a power supply, but you will need to confirm its polarity.
00:48 Either from documentation or testing as described in our wiring fundamentals course.
00:54 Regardless of whether our engine position and speed sensors are digital or reluctor based, we will always use shielded wiring to interface to them.
01:02 This gives us an added factor of safety against electrical noise contaminating such a critical signal.
01:08 In the case of the reluctor based sensors fitted to our FD3S example project, we will interface to each with twin core twisted shielded pair wiring.
01:16 With the shield braid being connected to ground at only one end, an ECU power ground pin near the ECU connector in this instance, your ECU will most likely have dedicated pins for engine position and speed signals and these pins could differ depending on whether the sensors are a digital signal or a reluctor type.
01:35 You will want to confirm the correct pin connections with your system designer or the person that will be tuning your vehicle.
01:41 Next we will look at the analog signal sensors fitted to our engine.
01:44 Usually consisting of a throttle position sensor, manifold pressure sensor, and other pressure sensors, oil and fuel being common examples.
01:52 These sensors will all require a connection to the sensor supply and sensor ground pins of the ECU.
01:58 And they will then have their output signals connected to an analog input pin of the ECU.
02:03 Shielded wiring is not typically required for these sensors as they usually have relatively high signal strength and internal filtering within the ECU helps to reject any noise.
02:13 Closely linked to our analog signal sensors are the temperature sensors fitted to our engine.
02:18 Primarily being coolant temperature and intake air temperature.
02:22 These sensors have two pins and are connected to sensor ground and a temperature input channel of the ECU.
02:28 Once again, the signal strength and internal filtering the ECU uses, means we do not need to use shielded wiring for these signals.
02:35 Although they are less common, sensors that output a digital signal do come up from time to time.
02:41 Ethanol content sensors for example output a digital signal, or a switch the driver uses to select a particular mapping option, like desired boost, can be thought of as a digital signal sensor.
02:51 These sensors will often require a sensor supply and a sensor ground with their signal output being connected to an ECU digital signal input pin.
02:59 This input will usually then have a pull up resistor enabled within the ECU software to give the signal a known default high state when the sensor is not connecting it to ground, ensuring that it is only ever one of two values.
03:13 Most modern EFI ECUs include a knock sensor interface and it is wise to take advantage of this if possible.
03:19 When we're wiring in a knock sensor we will always use shielded wiring, as the signal they output is quite weak and is very susceptible to noise.
03:27 Most of the time we will use twin core twisted shielded pair wiring to make the connection to the knock sensor with one knock sensor pin connected to sensor ground and the other to a dedicated knock signal input pin on the ECU.
03:41 Knock sensors come in various different styles though and interfacing to OEM knock sensors this way can sometimes cause issues.
03:47 Make sure you measure the continuity between the knock sensor connector pins and the body of the sensor where it interfaces to the engine block.
03:55 Often one of these pins will be connected to the body of the sensor and this can cause issues when we then connect that pin of the sensor to the sensor ground at the ECU.
04:05 As we're then in turn connecting our sensor ground to our power ground, the engine block, which is something that we want to avoid.
04:12 If you strike this issue, you are best to swap your knock sensor for an aftermarket motorsport item as their signal pins are isolated from the body of the sensor.
04:20 We're omitting a knock sensor all together for our FD3S example as their usefulness on a forced induction rotary engine is somewhat limited.
04:28 Given the way rotary engines respond to ignition timing and the speed at which damage is done if knock is encountered.
04:33 Most EFI system designs will include a permanently installed wideband O2 sensor.
04:39 Either interfacing directly with the ECU or via an external sensor controller.
04:43 If your ECU has a direct wideband sensor interface, this will typically take up five pins on your ECU header.
04:50 What these pins do and the actual operating of a wideband O2 sensor is outside the scope of this course.
04:56 But your ECU documentation will have details on how one should be wired up.
05:01 If you're using an external wideband controller, this will most likely interface to your ECU via an analog input pin.
05:07 Important is that the wideband controller and the ECU are grounded to the same location as this will help limit any ground level offsets in the output signal from the controller.
05:18 The Link Fury ECU we're wiring into our FD3S has an onboard wideband sensor interface so we will be wiring a connector for a Bosch LSU 4.9 sensor directly to this.
05:29 Following the connection documentation available in the PC Link software.
05:33 As we are going to have to connect our sensor supply and sensor ground ECU pins to multiple sensors, we are going to need to perform splice connections, and we'll need to play in where these splices are to be located.
05:44 I locate my splices directly behind the ECU connector and run an individual wire out to each sensor that requires a supply or ground connection.
05:52 This does mean that we will be running more wires than strictly necessary through the main trunk of our harness, but locating a splice behind the ECU connector ensures that we will be easy to strain relieve and locate if it ever needs repair.
06:06 We have omitted working out the current draws of all the sensors as they are typically very small and the limiting factor for the wire size we choose becomes the robustness of the wire itself and getting a reliable crimp connection to the terminals.
06:19 For most designs including this one, I will run all sensor wiring, including supplies and grounds, using 22 AWG wire.
06:26 This should cover the majority of sensors you'll need to interface with at the modified street car or club day track car level.
06:33 For our FD3S example we will be using the original reluctor sensors that read a trigger wheel attached to the front eccentric shaft pulley.
06:41 We will have analog sensors in the form of throttle position, intake manifold pressure, oil metering pump valve position, fuel pressure, and engine oil pressure, we will have temperature sensors monitoring engine coolant temperature and intake air temperature sensor, we are omitting a knock sensor, but we are installing a Bosch LSU 4.9 wideband O2 sensor, interfacing directly to the Link Fury ECU.