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Lambda Tuning


Perfect Power Articles.


Lambda Tuning and Air Fuel Ratio refers to the same unit function. It refers to the ratio of air to fuel in an internal combustion engine. Both air and fuel are required for a BANG or explosion of power in the cylinder and if the correct amount of air is provide to completely burn all the fuel, then this is ratio is known as the Stoichiometric ratio, which is normally 14.7 AFR : 1 Lambda.


14.7 AFR (Air Fuel Ratio) – 1.00 Lambda


Lambda tuning or Air Fuel Ratio is important to petrol engines, but it can be measured on diesel engines as well. The Lambda reading is simply the amount of oxygen REMAINING in the exhaust after combustion.

When the engine is not operating on 14.7 AFR, it is polluting the atmosphere. Unburnt fuel becomes air borne hydrocarbons (rich fuel mixture) and excessive air contributes to nitrogen oxides resulting from high combustion chamber temperatures.



Lambda tuning is of utmost importance to the engine because of environmental concerns (carbon emissions), fuel consumption (fuel saving) and power management. The following graph shows some fundamental relationships:

Lambda Tuning - Air Fuel Ratio Graph


Before diving into the technical details, it is important to realize that very modern direct injection engines will stretch the limits however it is safe to say that at full power the above table applies, more or less.

How is the Lambda ratio measured?

With two different types of (oxygen) O2 sensors (probes).

The one most common type is the NARROW BAND lambda (in German: Sprungsonde) probe, which is only good to confirm that the Lambda ratio is 14.7.

One may extend the range a little, but the probe is useless below 13 Lambda ratio (rich) and above 15.5 Lambda ratio (lean). Even at these limits the accuracy is well, off. The probe supplies a voltage from 0 to 1 volt, and approx. 0.45V equals 14.7 Lambda ratio. The advantage of the narrow band probe is its relatively inexpensive and that the Lambda ratio can be read off directly from the probe with a volt meter.

The other type is the WIDE BAND Lambda probe. With some technical trickier the range of this probe is extended to 10.3 Lambda ratio and 35 Lambda ratio. This probe requires a controller, and the current through the probe is the measuring criteria. Zero current equals 14.7 Lambda ratio. For the average person this probe represents a problem because the voltage is meaningless, and the current has to be compensated and is not linear. However, the probe is vital in turbo and supercharger engines.

There is a significant trend: 10 years ago, the NARROW BAND probe was common, today it is doubled up with a wide band probe (before the CAT) and a narrow probe (much cheaper, after the CAT). Every reputable engine manufacturer is forced these days to comply with emission laws, and reduced fuel consumption, and customer demands for more engine power.

The compliance is done by a closed loop system. The exhaust oxygen is measured, and then compared to some preset limits, and then the fuel injection is adjusted to meet that limit. This is performed more than hundred times a second. Actually, it is performed so fast that the Lambda is measured for each cylinder, and then the individual cylinder injection is adjusted. This is also used to test each injector by randomly switching one injection off and confirming that the cylinder goes lean for one combustion cycle. Smart technology!

The closed loop system of modern cars applies mostly to idling and cruising. From the loop adjustment during closed operation a global adjustment is computed, which then applies to the open loop operation. The exact open/closed loop parameters differ between manufacturers, but any tuner can monitor them.

Can I change the Lambda loop setting?

Yes and there are many reasons: increased engine power, less fuel consumption, better engine performance. Sometimes, but not very often, one should correct the manufacturers settings. It is not that a manufacturer makes a mistake, but rather that he bows to market (financial) forces and fixes these settings with a last minute adjustment.

Lambda in a closed loop system can be tuned to suit your needs. This is possible by modifying the probe readings. If you want your engine to run richer at a certain spot, then you ‘fool’ the probes to be leaner. The engine ECU sees the leaner reading and will adjust the fuel up. Bingo, your engine runs richer!

Of course, for every probe you need to have an adjustment circuit. Once you have installed the tuning chip i.e. SMT piggy-back, you will be able to tune every operating point of the ECU.


The following Perfect Power tuning chips will do Lambda Tuning:

SMT8 Piggy-Back Unit
SMT8L Piggy-Back Unit
SMT8T Piggy-Back Unit
SMT8-FT Fuel Tuner Unit

Other related tuning articles:

Ignition tuning
Airflow tuning
Ethanol conversion


Visit the following links for more information on Lambda Tuning:

Product Manuals
Application Notes