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EFI Tuning Fundamentals: Oxygen Sensor

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Oxygen Sensor


00:00 - The EFI systems fitted to most factory cars will include an oxygen sensor, or lambda sensor, fitted to the exhaust.
00:07 These sensors may also be referred to as a Universal Exhaust Gas Oxygen sensor or UEGO sensor for short.
00:15 The aim of fitting one of these sensors is to sample the content of the exhaust gases.
00:19 And from this, the ECU can deduce the air-fuel ratio.
00:23 There are two styles of oxygen sensor that you'll come across though.
00:28 Narrowband and wideband.
00:30 By far the most common in an OE installation is the narrowband sensor.
00:35 As its name implies this style of sensor is only able to effectively measure across a narrow band of air-fuel ratios and is only effective at the stoichiometric air-fuel ratio.
00:46 Narrowband sensors are common in factory engine management systems as they allow the ECU to make small changes to the fuel delivery in order to maintain a stoichiometric air-fuel ratio at idle and cruise.
00:58 This is done because the engine produces minimal emmissions at the stoichiometric air-fuel ratio and to ensure the catalytic converter operates correctly.
01:07 In order for the catalytic converter in the exhaust to work effectively the air-fuel ratio actually needs to swing back and forth across the stoichiometric air-fuel ratio, moving slightly rich and then slightly lean off stoich.
01:20 A narrowband sensor can be identified by the number of wires it contains.
01:25 The sensor itself only requires two wires and outputs a voltage that varies between 0 and 1 volt.
01:32 Most narrowband sensors will use four wires though because they also include a heater element that's used to bring the sensor up to temperature and get it working faster from a cold start.
01:42 Since the narrowband sensor is only effective at the stoichiometric air-fuel ratio they aren't particularly useful for us when it comes to actually tuning the engine.
01:52 For this purpose we need a wideband sensor which is able to accurately measure across the range of air-fuel ratios that we may end up running our engines at.
02:01 Wideband sensors can be identified by the fact that they'll usually contain 6 wires and are quite a complex device in comparison to a narrowband sensor.
02:11 Requiring a specialised controller circuit in order for them to function.
02:15 Some after-market ECUs include onboard wideband control circuitry while others will need you to use an external, standalone wideband controller that can then send the air-fuel ratio data to the ECU as an analogue voltage or via CAN.
02:30 While the wideband sensor is an essential input for tuning the fuel delivery, adding a wideband sensor to your ECU installation can also speed up the tuning process in some ECUs by allowing the fuel table to be auto tuned.
02:44 In addition, many ECUs will also make use of the sensor input to allow closed-loop operation which then allows the ECU to make alterations to the fuel delivery to account for any errors compared to our desired target.
02:58 We're seeing more and more late model cars also now including a wideband sensor in place of the older narrowband sensors.
03:06 And the temptation is to rely on the information from the factory unit while tuning.
03:11 While undoubtedly some of these sensors will provide accurate information, equally, I've seen a number of factory wideband sensors that varied considerably in their reading when compared to my own wideband fitted to my dyno.
03:24 For this reason, I'd always recommend at least comparing the output of the factory sensor with a known and trusted wideband meter before relying on the reading.
03:34 So in summary, you need to understand there are two different types of oxygen sensor.
03:39 And for our purposes we need to use a wideband sensor.
03:43 Remember, you can identify the sensor by the number of wires it uses.
03:47 If you're using an aftermarket ECU that's capable of taking input from a wideband sensor it's a very useful addition which can help speed up your tuning.

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