One of the key sensors we rely on when tuning any engine is an air fuel ratio sensor, often in the form of a wideband oxygen sensor, or lambda sensor, as it may also be known.
These are typically fitted in the exhaust system somewhere after the turbocharger in a turbo application or after the collector in a naturally aspirated engine. There's nothing necessarily wrong with this, however it is important to understand that this actually gives us the average air fuel ratio of all of the cylinders feeding into the collector which means that we may
have one cylinder that's running too rich, another cylinder that's running too lean,
but the average air fuel ratio will still read right on our target.
The reason we see this situation is that in most engines we'll see some small variations in air flow between the various cylinders. In a normal road going engine or even a light to moderately modified engine, these air flow differences don't normally present too much of an issue.
Once we start heavily modifying the engine though where we can run higher power levels and boost pressure, the tuning envelope becomes much tighter so that one cylinder running lean could quickly result in damage and or failure. The most accurate way of dealing with this is to monitor the air fuel ratio or lambda on each cylinder via extra sensors.
In this particular application we're looking at here on Boyd Auto Racings Mitsubishi 4B11 powered EVO X 2018 Pikes Peak entry, the engine is turbocharged so the sensors have been fitted to the exhaust manifold pre turbocharger.
In this installation the wideband air fuel ratio sensors are being monitored by an AEM Electronics four channel UEGO system. This monitors both the air fuel ratio as well as the exhaust gas back pressure, which the unit to compensates for, ensuring that the air fuel ratio data is accurate.
This data can then be transmitted either by analog voltage or via CAN allowing the tuner to then monitor the individual cylinder air fuel ratio to trim tables in the ECU evening out any errors or variations.
Using a system like this to optimise the individual cylinder tuning, can result in a more reliable engine, and in some instances, we may also see a small but noticeable improvement in engine power as a result.
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