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Practical Wiring - Club Level: OEM Integration and Auxiliary Connections

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OEM Integration and Auxiliary Connections

03.56

00:00 - When we're designing an EFI wiring harness for a club level track car and particularly a modified street car, it's highly likely we're going to need to integrate with some of the OEM electronics in the vehicle.
00:10 Because this topic is very application dependent we'll look at a couple of the most common scenarios you're likely to encounter but it you do have further questions, we encourage you to create a post in the practical wiring section of our forum with your particular application.
00:24 This way we can help you out there with your particular project and the other members of the forum can benefit from the conversation also.
00:31 The most common example of integrating to OEM electronics is retaining the operation of the original gauge cluster in the vehicle.
00:38 For vehicles from the 2000s onwards, most of this functionality is likely to be provided via a CAN bus network connection.
00:45 In this situation you will need to contact your ECU manufacturer's technical support department to determine if their ECU is capable of generating the required data stream.
00:55 It's often possible to capture and decode these data streams, but it's a very advanced topic and outside the scope of this course.
01:02 In the case of our FD3S example the operation of the original tachometer is controlled by the ECU via a generated PWM signal on one of its output channels.
01:13 The coolant temperature gauge, vehicle speed signal and reverse light switch signal come from senders which are mounted in the engine block and transmission respectively.
01:21 These signals are routed through the original EFI wiring harness that we are replacing, however they do not make a connection to our ECU.
01:29 We will need to include them in our design to retain the operation of these parts however.
01:35 The other gauges in the vehicle such as oil pressure, fuel level, and the various warning lights are run through separate harnesses which will be retained, so their operation is not going to be affected.
01:45 The FD3S vehicle speed sensor is a reluctor type that generates an AC wave form which the gauge cluster interprets then driving a small motor connected to the speedometer needle to the correct location.
01:57 The gauge cluster also generates a digital signal output.
02:00 The frequency of which is relative to the engine speed.
02:04 We will run this signal back to our ECU as when we have the vehicle running on the road, we can calibrate the ECU to read this signal correctly, giving us a valid vehicle speed signal input to the ECU which can be very useful for some tuning strategies.
02:18 Similar to this, the body control ECU in the FD3S outputs a digital signal when it is experiencing a higher electrical load than normal, such as when the headlights are first turned on or the rear defroster circuit is active.
02:32 Running this signal back to an ECU input will be helpful as it will let us increase the idle speed to avoid the engine stalling due to the extra mechanical load generated by the alternator.
02:41 Other signals from OEM sensors in the vehicles we will interface with are the clutch pedal position and neutral gear selection switches.
02:48 As having the ECU be aware of these situations will open up opportunities for more advanced tuning strategies down the line.
02:54 And as these sensors are already in the vehicle, their inclusion in our design is fairly trivial.
02:59 We will be retaining the original cooling fan power supply wiring and relay system as for this application they are known to be effective and reliable, and have a well thought out setup that includes multiple selectable fan speeds.
03:12 We can easily accomplish this as the cooling fan relays were controlled by the original ECU and we can replicate this control scheme on our aftermarket ECU.
03:21 Much as we have done for our network communication system where we have added two auxiliary CAN access ports to our harness, we will do the same for the sensor inputs and outputs on our ECU that have not yet been used, populating them into another auxiliary connector, located in the engine bay.