911SC Oxygen Sensor

[GaryDG]

These questions apply to an '83:

Can the Oxygen Sensor be replaced without the special tool described in Bentley's?

Is the box underneath the driver's seat the Oxygen Sensor Control Unit?

The process for testing the Oxygen Sensor, described in Bentley, is unclear to me. How can one apply a voltmeter to test, without disconnecting the Oxygen Connector Harness? That is, how does one go about testing the Oxygen Sensor?

[vizail]

Start with This

http://www.pelicanparts.com/911/technical_specs/911_cis_troubleshoot.htm


Vic

[vizail]

And here is a great site

http://members.rennlist.com/jimwms/CIS/CIShome.html

Vic

[vizail]

Malfunction: Usually the O2 sensor itself. A good one produces about 500 millivolts at 14.7 air/fuel, The sensor actually detects free oxygen in the exhaust gas

Vic

[vizail]

I hope I can be of some help.
In my four year's(4) to date long restorarion this forum has been of great help . the data and procedure library in this forum is great . Just search in the forum and the rest is history.
You can contact Mr. Wayne and he can be of great help.
Is my understanding that you can obtain a reading from the CO2 sensor .
While the engine is running and at operating temp., Connect a Votimeter and select the millivolts setting. After the engine is hot connect the red + wire to the OXC sensor Cable (green) and the Black - negative to ground .If OXC sensor is operating properlly
you will have a reading in a range betwen 500 to 950 millivolts.
Malfunction: Usually the O2 sensor itself. A good one produces about 500 millivolts at 14.7 to 1 air/fuel, The sensor actually detects free oxygen in the exhaust gas. Needles to say, I just disconect the damed thing and operate the CIS in what is called Open range. The control units are located under the passseger seat. You will find the OXS Control Unit ,Rellay, and the Acceleration Enrichment Control (Check the photo)
Malfunction: Usually the O2 sensor itself. A good one produces about 500 millivolts at 14.7 air/fuel, The sensor actually detects free oxygen in the exhaust gas

Vic

Here is my 1982/ 911SC System Check

[GaryDG]

Vizail, the links are really helpful. I wish I had seen the Trouble-shooting guide and the Rennlist stuff when I first started trying to debug my CIS.

In your post above, you refer to the red and black wires - I presume you are referring to the multimeter's wires.

Also, would you know:
if a disconnected air pump would cause false readings on the Aire Sensor test?
if the air sensor could be removed without the special tool?

You mentioned you run your CIS system "Open Range" ie the O2 sysem/Lamda not engaged. In reading the Rennlist stuff you referred to I found:

"On Disabling O2 sensors:
Disconnecting the O2 sensor electronics box (and not just the O2 Sensor) on CIS engines designed to use them will reduce the cold start enrichment, and the full throttle enrichment. The engine may also probably lose some gas mileage."

Do you find this "reduced enrichment" and decreased gas mileage?

Thanks again

[fireant911]

Originally Posted by GaryDG

... Do you find this "reduced enrichment" and decreased gas mileage?

Thanks again

GaryDG,
I have been tracking my mileage religiously. The first seven months of ownership involved driving with a disconnected Oxygen Sensor. After finally discovering this, the remainder of time (3-1/2 years) was with the 'loop' connected. My mileage improved 22.8% - so yes, the decreased mileage, at least in my case, is well-documented and proven.

[vizail]

Yes

Tha OXS sensor is desing to produce a voltage output wich varies from 0.1 millivolts (high oxigen lean mixture )to 0.9 millivolts (low oxige rich mixture).
The PCM constantly monitors this variable voltage to determine oxigen to fuel in the mixture. This is in the electric type fuel Injectors. If you have CIS System on a 3.0L engine with mechanical fuel Injector just disconect the thing and used it open loop.
As I said before the Ideal mixture ratio is 14.7 parts of Air to 1 part of fuel.
Do not disconect the control unit under the seat ,just disconect the OXS sensor( Green wire on the engine bay close to the fuel filter and the fuel pressure accumulator.
Be careful with the vacumm lines and hoses, Air leack's on this engines become a Brain Storm ,so keep them working .Carefull inspection is a must and if necesary replace them

Hope this can be of some help.

Cordially

Vic

[LM3929]

If you disconnect the O2 wire out of the connector and slip the correct sized box end wrench (not the open side ) you can remove the O2 sensor without damaging it.
If you use the open face you distort the sensor and it will fail.

LM

[MarcoPau]

Hi everybody, this is my first post after I just made my dream come true and bought a 1982 911 SC :-) I have problems at cold engine idleing, thus I decided to check the o2 sensor and I found its wire to be disconnected.

Can anybody point me where it should be plugged in? I don't know the car at all so please consider me as a complete newbie, at least for the moment ;-)

Thank you guys!

[Autoban]

As far as the tool. When I needed to replace the sensor on my '86 I found out that our local Advanced Auto Parts store had a loaner tool.

[MarcoPau]

I think this is the broken connector... Do you think I could solder the wire to it? I guess I could stick a small piece of MIG welding wire in it to better support the soldering.

How about testing the sensor? I tried to use a voltmeter (+ on the wire, - on the sensor's shell) and warming it up with fire, but it didn't seem to give any tension...

Thanks a lot

[psalt]

how does one go about testing the Oxygen Sensor?

Gary,

The best way to test the system is to hook up an analog dwell meter to the test port and observe the FV pulsewidth with the engine running open and closed loop. This will give you an indication of condition of the sensor in action, the ECU and allow you to make mixture adjustments. Search for "lambda CIS" and you will find all the details. CIS lambda will talk to you , much better than uninformed guess. The O2 sensor is irrelevent during cold starts, acceleration and loads above 35%. It has no effect on WOT performance.

[MarcoPau]

Psalt, my problem is actually this one: cold start is perfect, engine idles at around 1500 rpm in the first half minute or so and runs well, then gradually revs slowlier and below 1000 rpm starts wobbling and misfiring. In a minute or so it'll set as low as 500 rpm or even less, wobbling and running really bad, a lot of misfire if I run the car.

After 5 minutes of warming up the car will start working properly, good response of throttle, less misfiring and higher idleing rpm. Eventually, when the engine is well heated, the car will run absolutely perfectly and idle at standard 8-900 rpm.

Do you have any hint? I'm soldering the o2 sensor wire in the meantime.

Thanks a lot!

[Bob Kontak]

+1 on what psalt says


Can the Oxygen Sensor be replaced without the special tool described in Bentley's?
I think a 7/8" box end wrench fits.

The process for testing the Oxygen Sensor, described in Bentley, is unclear to me. How can one apply a voltmeter to test, without disconnecting the Oxygen Connector Harness? That is, how does one go about testing the Oxygen Sensor?

Get a wire that is stripped at both ends and stuff one of the strand ends of wire into the O2 sensor female connector and plug it in to where it plugs in normally. The other end of the wire is where you connect the multimeter.

[Bob Kontak]

MarcoPau - Do you know that you are hijacking this thread?

That connector is the connector you need to connect to. Make it happen best you can but this is not your thread.

[psalt]

MarcoPau,

My advice is to check the FV pulsewidth with a dwell meter, and the control and system pressure with a CIS gauge. Your problem is a cold running or warm up issue. Most cold running problems are because the mixture is too lean. Once the key is off "start" the CSV is irrelevent, so you can eliminate that and the O2 sensor is ignored during warm up and is also irrevelent. The control pressure regulator (WUR) is supposed to lower pressure to enrichen the mixture during warm up and the AAR allows extra air to boost the idle when cold. Even if these are working correctly, you can have your symptoms if there are vacuum leaks and the mixture is incorrect. It sounds like they are working, but when they start to lean out the mixture and reduce the idle, the engine is not ready and the lean condition causes poor running. The emissions vacuum retard can also make this worse. I would hook up the O2 sensor, a dwell meter to the test port and start the car and verify that the lambda system is working correctly. Then I would disconnect and plug the vacuum lines to the distributor, check the ignition timing at 950 and 4000 rpm, then reconnect the advance and leave the retard disconnected and plugged, and reset the hot idle to 950 rpm. Set the hot closed loop mixture to 25-35 dwell with an allen wrench. Check for vacuum leaks around the injectors and boots with a unlit propane torch while wiggling them. If the injector Orings and sleeves are original, they are leaking. You will never get OEM drivability off idle with vacuum leaks. You also want to check the added cold acceleration enrichment system on your engine. Porsche struggled with the cold start and running part of the emissions test during this period and the cars are calibrated very lean with new compression and no vacuum leaks. As the engine ages, compression and vacuum drops and the original calibration gets even leaner and a compromise of adjustments is needed.

[Bob Kontak]

Originally Posted by vizail

,just disconect the OXS sensor

Why would you tell anyone to disconnect the O2 sensor? What benefit is there to doing this? What are you thinking?

Edit: I think a more kind way to say this is since there is reduced gas mileage and no increase in performance why kill the function of the O2 sensor?