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Practical Diesel Tuning: Air Fuel Ratio Sensor

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Air Fuel Ratio Sensor

02.07

00:00 - Traditionally, air/fuel ratio and lambda sensors haven't been a common addition for those tuning diesel engines and instead the EGT gauge has been the primary means of monitoring the state of the tune.
00:09 The reality however is that an air/fuel ratio meter does tell us a lot about what's going on with the fuel delivery and it also responds much faster than an EGT sensor.
00:19 Particularly if you're tuning an engine that's fitted with a DPF, monitoring the air/fuel ratio can be a real advantage.
00:26 For the majority of a diesel engine's operation, it will be running significantly leaner than stoichiometric, as you'll recall that with a diesel engine we modulate fuel delivery in order to control engine torque.
00:36 In this regard, it's only when we're really asking for maximum power from the engine and consequently injecting more fuel then our air/fuel ratio may start to approach stoichiometric.
00:46 Even under these conditions, we're typically going to be running leaner than stoichiometric.
00:51 There are a variety of air/fuel ratio meters available from a huge number of manufacturers so your options here are almost endless.
00:56 If at all possible, we really want to choose a wideband meter that allows us to output the data to our dyno or our datalogger or scanner so we can overlay the air/fuel ratio with other aspects of engine operation such as RPM, fuel delivery, boost pressure.
01:11 This will allow us to make accurate changes to the fuel delivery in specific areas of the table in order to correct overly rich conditions or take advantage of lean conditions.
01:21 This is going to be much more powerful than just viewing the AFR data as we perform a dyno pull or drive down the road.
01:27 There are two ways that a wideband gauge or meter will generally transmit AFR data to an external device.
01:33 The traditional method has been to transmit the information via an analogue 0 - 5 volt signal with the voltage relating to the air/fuel ratio.
01:40 In the logging device, we can then calibrate this voltage to display the AFR data.
01:43 The issue with this technique is that the output is easily upset by ground offsets and this can dramatically skew the reading in your scanner.
01:51 For this reason, my preference is to use a wideband meter that can transmit the AFR data via serial or CAN.