OK I am getting ready for my Sat BBQ work party and I realized the FI wont work properly unless the sensor is installed!

Does anyone know if it should be on one of the headers or should I weld it into the muffler??



Here is what I have!

The muffler not only would be tough to weld on, but it would be too cold for an o2 IMO. Btw that looks stainless. You got stainless wire on the welder?

I was going to take it to the local guy and get it done tomorrow so he would have what ever I need!

I think the original was mounted in the HE exhaust so I may just do that but I wanted to ask the collective knowledge of the board before doing it!

I would put 2. One on each collector. Then you just need an Autometer dual WB gauge or an AEM unit. Range between $200-300.

I have extra bungs and threaded plugs if you need them.

Mine is installed just after the junction on the drivers side header. By the way, the engine will run without it. The euro spec cars did not run them. Go over to the 911 tech section on Pelican and you can read for days about this subject.

Yes 2 sensors would be "ideal" but I am more worried about getting it running this weekend! So if it will run without it I will just install it in the Drivers side and deal with the added one later!!

The more collective imput the better......Keep it coming!!

If you're going to get it welded, do both. I will bring you a plug for the unused one. That way you won't have to pull it apart again.

I will look into getting another bung nut! Does the stock FI system have the ability to read 2 sensors?

nope, one sensor.
Its a stupid sensor also...narrow band.
Given I have been chasing the fluxuating idle that curses these 3.2 motors, I read a fair bit about it...wired in some gauges, monitored the output of this specific O2 on the Motronic and its really a two position sensor.
Rich or lean.
It gets heated up by the two white wires...and send the signal on the black wire.

You should be fine if you put in one sensor just before the muffler.
Just be more cautious and watch your fuel pressure at both fuel rails...put in some inline gauges to be certain...right in the engine bay is fine.

So long as the fuel pressure is correct on both banks, the O2 sensors job is to tell the ECU richer or leaner...and it flips back and forth constantly....so its always changing the ignition timing and the duration of the injector spray....
When I say its always changing...its always hunting around perfect A/F mixture, so the signal bounces up and down constantly.

One should be fine, the ECU cant read two....unless you start soldering.

YMMV I just read above that you have a 3.0 so I would not be able to tell you how the CIS system reads the O2.
I cant imaging a more complicated O2 circuit on the older CIS system, so I suspect that one will still be fine for your application.

Rich

Just to elaborate - this rich/lean dithering is done on purpose for the cars in which it was originally designed - it's the environment a 3-way catalyst needs to work its magic on both HC and NOx.

Please elaborate more.
I just figured it was the best they could do and like all the previous FI systems prior to the Motronic...it was a guess to try and keep the motor from running to lean.

Rich

One of my 911-list friends is the real expert on this subject, and I can't condense his synopsis in the time available to me right now. I'll go back and do that, I just can't right now.

Short version: a 3-way catalyst is working on 3 gasses - HC, CO, and NOx. Two of those - HC and CO - need an oxygen-rich environment to complete their chemical trip to CO2. This means lean - more air than stoichemitrically correct for the fuel. But the NOx catalyst component needs a reducing (rich) environment to disassociate the oxygen from Nitrogen Oxide and turn them back into (relatively) inert nitrogen and - ta da - an excess of oxygen available for the next oxidation (lean) cycle.

If and when you have time, point me to your friends threads on whatver board...

It was interesting to watch ( I ran a datalogger to my laptop so I could watch over time)
At Idle...it was rhythmic....lean, rich and so on.
When revved up...it went right to rich and stayed there.

Rich

Threads?
This is the dinosaur RennList (now Reutterwerk) 911 email list.
There are no threads, aside from what individual members happen to save and archive.

I've archived all the digests back 18 mos, and I also keep those individual posts I feel are of special value. So I've got the data, but I doubt any of it is available in a persistent online archive...

That is the CIS/Motronic 'accelerator pump'.
The cats are designed for steady cruise. Once your right foot calls 'More power, Mr Scott!' the emission rules go out the window and you get power - until equilibrium is again attained.

Your CIS can run without an O2 sensor connected, it goes into open loop mode does not compensate for mixture changes. You unplug the O2 to set the base mixture. O2 sensor system on this CIS is simpler that the DME system and the O2 signal is only used for mixture compensation.
I don't think any of CIS 911's ever got a heated O2 sensor (3-wires) just the single wire sensor but maybe 82 or 83. Without a heater in the sensor you might have issues with the sensor cooling off too much or taking too long to warm up, if so you can add a heater circuit and a more $$ heated sensor.
I would add a 2nd sensor so you can monitor 1 bank of cylinders while the CIS uses the other for mixture control, will give you a heads up if 1 side is richer or leaner that the other. CIS systems have multiple places for vacuum leaks so it is easy to get some cylinders that are leaner than others.

Do you have access to a exhaust analyzer to set the fuel mixture with?

Jim

No analyzer!

Your answer makes me feel more comfortable with starting the engine without the sensor installed!!

That will free up some time today to get other things ready for tomorrows BBQ work party!!

If I manage to remeber to pull it out, I'll bring my analyzer with me on Saturday.

Jim

One bung-o-doodle and sensor has worked for me so far ...

Yea thats what I was thinking about doing! I will do that after I get it running since it is not needed to start the motor!

I've got it, but it was easier to just ask - so I did.
I asked if my 1-paragraph was correct. It is. Here's some additional information for background:

" Important thing to remember is - our CIS systems are a
mechanical fuel injection at best. True fuel control is mechanical and
maintained by - fuel pressures and initial CO adjustment.

According to Porsche, they went to the Lambda sensor / TWC in '80 to save
weight. The TWC system drops the air pump and EGR.

The Feds were so suspect of this "non-mechanical" emission system they
argued that the little O2 sensor would shortly burn out, thus dropping birds
out of the air too soon. Bosch said, nein - this is one tough cookie
and can last 100,000 miles. No no said the Feds - but we'll let you bring
in your evil cars if you change out the sensor at 30,000 miles. So a gizmo
went in to the speedo that clicks on the OXS light at 30k and a warning in
the owners manuals states such. Of course this may only work for the Jimmy
Caaarter 85 mph speedos - of which there are probably 7 SC's nationwide
that still have those.

Of course after the Carrera years, the O2 sensor steps up its work load with
electronic fuel control items and now it is the quintessential gizmo that
makes our engines what they are today - powerful and clean.

Oh - the TWC system DOES need a slightly rich O2 level (14.6 to .8), but
that is set mechanically with the stuff on the engine, not the O2 sensor, as
it does today. Oh, and #2, to correctly operate - the fuel control must
operate in a very narrow band. "

So there ya go. I have personally verified that with no sensor, the box itself provides a small, constant, midrange voltage for itself. When the sensor is plugged in, its signal strength overrides the internal reference.

The dithering is done to make the cat bed work at optimal efficiency. No cat - no need for dithering... When I did my CIS-K[e] tinkering, I kept the sensor in part so I could watch the response and verify everything was working. Without it, I'd had to plug the hole in the bung with something, and I had this perfectly good sensor...

I gave Jeff 2 real O2 bungs and plugs today. That way he can put one in each collector. Plug one and use the other. I would test each side with a gauge and put the sensor in the side that runs the leanest. That way you can keep an eye on it. Let me know if you need a gauge.