Reconnecting O2 w/ Rich mixture - CO

[schoward]

My 81SC is currently set with the mixture rich with O2 disconnected as many around here do. My CIS is stock and in good working order and I've run the O2 sensor in years past with no issues. Its where it is now simply because my wrench put it that way last time it was serviced and Ive had no time to mess with it in the past 2 years - and it runs damn good. He likes the 'rich and no O2 setting' which I know is always up for debate lately.

Emissions question: If I reconnect the O2 with mixture set rich (say 3%), will the lambda pull the mixture back to near stoich from its rich setting (in open loop after warmup and below 35% throttle) and put the CO emissions in intended range? Or does the rich setting throw it out of wack so badly that the sensor does not get mixture and CO back to range at any point?

I guess I'm curious to know if reconnecting the O2 with mixture set as is will squeak me through NJ emissions this month (CO limit of 1.3 I believe), or must I get out the Gunson and go to work to get the CO down.

[mike635]

Not sure if this is helpful but I recently spent some time experimenting with the 02 system on my '81. You can learn a lot by monitoring the frequency valve via the diagnostic port using a dwell meter (or an oscilloscope, which is what I used) I was almost convinced that the lambda system wasn't working correctly because I could not get the duty cycle (simlar to dwell) to be 50% with the O2 signal fluctuating.

I discovered that the mixture was set too rich (probably by a previous owner/mechanic) for the system to compensate. 1/4 turn of the mixture adjustment (towards lean) and the system started worked perfectly.

My car runs better than ever and the mileage is about where it should be for the short city driving cycle I (unfortunately) do, about 17 which is what was on the original window sticker.

mike

[mickey356]

Intresting. My wrench likes rich w/ no O2 as well. That's the way it's currently running but I don't like the 13 mpg much. I've considered hooking it back up so I'll be following this thread for info. Thanks

[grahamkissack]

I'm in the exact boat and not liking poor mileage have reconnected my O2 sensor. Just starting reading the required Bosch and Porsche CIS manuals to become more familiar with the system and how to best tune it. Lots of knowledge here to help but I think you need to ask the right pointed questions since CIS can be complicated. I'm not to that point yet!

[psalt]

Emissions question: If I reconnect the O2 with mixture set rich (say 3%), will the lambda pull the mixture back to near stoich from its rich setting (in open loop after warmup and below 35% throttle) and put the CO emissions in intended range? Or does the rich setting throw it out of wack so badly that the sensor does not get mixture and CO back to range at any point?


Yes, it will. You need to hook up an analog dwell meter to the test port and actually see what the system is doing. If you have a good cat, it will still pass emissions with the mixture set to 20-30 dwell.

[onemark]

Hmmm, I'll be watching this thread too...
My 80SC is running great with no O2 sensor, no cat, very open muffer, timing advanced, no decel valve.
I'm changing from stock heat exchangers to SSI which happen to have a O2 sensor in place, so I'll be able to plug that in and see what it changes (and what I have to adjust to cope with the sensor in the loop)
I'd like a few more mpg too, but not at the cost of my current throttle responce.
;-)
Mark