EFI Tuning Fundamentals: Oxygen Sensor
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Oxygen Sensor
03.59
| 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. |
