2008 February

Wideband Lambda

First you need to know what Lambda is. Here's what the Innovate manual says about it.

For gasoline-driven engines, the theoretically optimal air fuel ratio is 14.7
pounds of air for every pound of fuel. At this ratio, theoretically, all available oxygen in the air
combines with all available fuel. This ratio is called the stoichiometric ratio. Stoichiometric for
different fuels are as follows:
Gasoline 14.7
LPG (Propane) 15.5
Methanol 6.4
Ethanol 9.0
CNG 17.2
Diesel 14.6
The measurement Lambda is the actual air fuel ratio over the stoichiometric ratio. A Lambda
measurement of “1” equates to the air fuel ratio of 14.7 (for gasoline engines). When Lambda is
less than 1 the engine runs “rich”, i.e., unburned fuel exists in the exhaust stream. If lambda is
greater than 1 the engine runs lean, i.e., free oxygen (02) is present in the exhaust. Depending on
the engine, maximum power is typically delivered when the engine runs slightly rich (for example
at lambda values of 0.8 to 0.9 for most engines). This instrument provides a means to measure
the actual air fuel ratio or lambda in the engine in operation directly from the exhaust. For this a
special wide-band oxygen sensor is used to measure the lambda value derived from the oxygen
content (or lack thereof) of the exhaust gases.

Modern cars have at an air/fuel sensor inserted into the exhaust before the catalytic cobvertor that measures the amount of oxygen in the exhaust gases after combustion. Some also have a second sensor after the cat. The signal from the sensor is sent to the ECU where the program adjusts the amount of fuel injected. Most cars have what is called a narrow band "oxygen" sensor which can only read a narrow band of lambda values and the signal is used for adjusting the fuel when the engine is idling. Wideband sensors can read a much wider range of lambda values and the signal can be used to adjust fuelling at all revs. With a standalone system the signal can also be used to drive a gauge to display lambda values or the air/fuel ratio.

I toyed with the idea of a wideband setup for a while. The MoTeC PLC is prohibitively expensive so I looked at the Innovate and the PLX Devices wideband. At JAE 2007 I noticed that Dawsey (Lee Dawes) had an Innovate wideband gauge on the dash of his 3S-GTE engined Corolla GTi. Another mate has a Honda CRX with the PLX - recommended for his Hondata ECU. Having talked to both of them I decided on the Innovate.

On my trip to Florida last October (2007) I picked up an Innovate Standalone XD-16 Gauge Kit from
Titan Motorsports in Orlando. There were a couple of places in Orlando I could have gone to, but choose Titan because they use Innovate stuff themselves and they specialise in Toyota Supras. Also they answered my email enquiry but the other place didn’t - no contest. They gave me a discounted price and combined with the good exchange rate (good for me anyway) I picked up a bit of a bargain. The standalone kit comes with sensor, a controller that is programmable from a laptop computer, all required wiring and a gauge to display the lambda values. It can also be connected to an engine management system, in my case the MoTeC M4.

The manual says that before fitting the sensor it has to be calibrated in “free air” and that means connecting it up to a power supply. The power supply for the system needs to come from an ignition switched power source and the plan is to do all the wiring and mount the gauge before I install the sensor. Dawsey has used the same power feed and earth that is used for his MoTeC M4. This is a good idea as then there should be no ground voltage differences between the two if I ever get them connected up for closed loop lambda control.

I spoke to Mark Harrison from Owen Developments at the Autosport 2008 Show (he fitted and mapped my MoTeC) and the good news is that the MoTeC does not need any upgrades, I just need to get it remapped and Mark is happy to do that.

PICTURE OF KIT