Emissions/Catalytic converter with standalone

In our country we have a yearly technical inspection that includes measuring CO and HC values and you have to be lambda1 +/- 0,03. Two measurements are carried out at idle and at ~2500rpm.

I have the feeling that it is slightly more difficult to get the required CO and HC values with standalone ECU vs OE ECU. I do not have a good direct one-to-one comparison, but the tendency is still that you need to heat up the cat and fiddle more than with OE ECU.

If we take a simple engine without vvt, there is only ignition timing and injection angle (besides injection pw) that can have an effect on the emissions.

As I understand correctly the operating principle of the catalytic converter, it requires the mixture to oscillate between slightly rich and lean to work efficiently.

With standalone we are targeting Lambda 1 but there is no oscillation similar to what you get with narrowband oxygen sensor as in most OE applications.

Has anybody struggled with this? Is it possible that without this oscillation it is more difficult to get the correct readings?

Is there something else I might be missing?

You should be fine, an aftermarket ECU "may" hold to the target more effectively, but that's a good thing.

For the most part, you're just copying what the the EOM ECU is doing.

The only reason OEM toggle between slightly rich and slightly lean, is because they have narrow band sensors, and may have a simple algorithm, if sensor indicates rich then remove fuel, if it indicates lean then add fuel. To it just bounced around the lambda 1.0 point even in steady state operation (ie. idle).

Is this incorrect that the catalytic converter works better with slightly oscillating AFR?

My understanding has been that this oscillation (or the lack of oscillation on the post-cat oxygen sensor) is how the catalytic converter efficiency is being measured in OEM application and this is how it works most efficiently. This made me think if this could be the difference in OEM and Aftermarket ECU that I get with exhaust gas analyzer.

Henrik

Oscillation at 0.1 Hz around a time-average stoichiometric point yields a higher hydrocarbon, NO and CO conversion than steady state. This is also referred to as dithering.

If idle and 2500 rpm operating points are your only concerns, then you are in a fairly comfortable spot and your vehicle will very likely pass this simple test. Obviously you must precisely calibrate those operating points.

If, on the other hand you would have to pass a homologation drive cycle, dithering is unavoidable.