[Diy_efi] Closed loop fuel and Cats ...

urq urq
Wed Mar 8 06:16:36 UTC 2006

... I'll bet if you look long and hard enough you can find at least one of 
every possible combination ...

My 1978 Audi Fox had straight K-Jetronic (no lambda) and a cat.  Since it 
was a California car it had EGR ... but that was it ... i.e. no OXS feedback 
That was my first new car, and when compared to its contemporaries was 
extremely simple.  Just about every other car I looked at had a carburetor 
and enough plumbing to make you think it was cracking its own fuel!  The 
other thing that was surprising was to see how much better a "little" 1.6 
liter engine could do compared to the others with their larger chemical 

I know the '79 Audi Fox was identical to my car, but I'm pretty sure that 
when they went to the "80" model in the USA in 1980 that it had lamba 
feedback ...

Steve B
San Jose, CA (USA)

> There were some early cat-equipped cars that did not use closed-loop, 
> instead there were two catalyzers and a air injection connected between 
> them. The engine was tuned to operate with a slightly rich mixture (always 
> lambda < 1), so it would produce much HC and CO but not much NOx 
> emissions. The first catalyzer then effectively cracks the NOx, and the 
> second one, which operates with lean mixture due to the air injection, 
> will burn the HC and CO.
> Of course, the two catalyzers often were combined to one unit with the air 
> injection tube connected at the middle.
> This system was abandoned when gas became expensive in the early eighties, 
> as it gave bad fuel economy.
>>>and thinking about it anyway, with a CAT fitted
>>>running closed loop is mandatory.
>> I believe that the first wave of cat-equipped cars had
>> a few without an O2 sensor.  I know that there have
>> been a number of motorcycles, largely Kawasakis, of
>> recent vintage that have a high-flow cat and no O2
>> sensor.  They clean up emissions *enough* to keep them
>> within standard requirements, which have only just
>> increased substantially in cleanliness.

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