[Diy_efi] Making a fake O2

[Bernd Felsche]

On Sunday 29 May 2005 14:12, Mike wrote:
> mmm,

> I seem to recall someone on this list talking about storage cat system
> and EFI some 2 years back,

Could've been me.

It applies to engines with stratified charge and lean burn
operations that produce higher NOx because they operate in excess
O2. The storage cat collects the NOx.

> ie. The EFI ECU drifts rich and lean to force the catalytic convertor
> to do its job properly for a storage type cat, I'm not familiar with the
> precise algorithm or even the cat cycle but I recall that even for
> optimum air fuel ratio the ECU will force lean/rich/lean cycle over
> a longish period of time to most effectively use the cat...

The rich cycle is triggered by (at least) the level of NOx passing
through the storage cat during lean burn being excessive (i.e. the
storage is full). To that end, there's a NOx sensor at the outlet of
the storade cat. NOx sensors have a much smaller inherent output
voltage than O2 so their "smarts" (uC) to convert that to something
that'll be used directly by the ECU are typically embedded in the
plug of the sensor.

I'd lend you my green Bosch book but it's in German so probably of
limited use to you.

-- 
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