No O2 sensor on my SC??

I’ve been struggling with high oil temperatures and vapor lock during the summer months on my 82 SC, so removed the engine to clean the oil cooler and test the thermostat. In doing this, I’ve found that my motor does not have an o2 sensor. Is it possible for the car to run without one? What will it run like? I checked my Bentley manual and it shows that the o2 sensor should be screwed into the cat converter. My cat converter has no brackets or screw ports of any kind. Anybody have any ideas? Thanks,

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Bruce
1982 SC

My 83 runs fine with it disconnected. Idle hunts a bit with it connected. Probably should replace it one day. Not a high priority since it seems to be running fine.

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Robert Stoll
83 SC
83 944

I understand the SC used O2 sensors for "fine tuning" emissions. Not really for driveability.

Nick

Both of the replies above are accurate and on point, according to my understanding. You don't NEED the O2 sensor. Some folks disconnect them deliberately.

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'83 SC

SC's didn't come with O2 sensors until '83 I believe.

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Leland Pate

___79 SC Targa

I had a new '82 SC - it came with an O2 sensor.

Charlie '87 Carrera

My dad's 80 has an O2.

Nick

Bruce, the O2 sensor provides the feedback to the fuel injection control unit. Some people remove the sensors to stop the control unit from battling against a rich basic setting (a cw half turn of a 3mm allen key in the hole between the fuel distributor and funky rubber boot will make it pretty rich).

Unfortunately, if your basic setting is too lean and the O2 sensor is missing, the control unit is not battling to enrich the mixture. This can lead to a very hot running engine (and valve/guide damage).

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Graham Archer
83 911SC Cab

US cars started having O2 sensors in '80. ROW cars got them later, not sure when.

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Bill Krause
'79 911SC Euro

US cars started having O2 sensors in '80. ROW cars got them later, not sure when.

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Bill Krause
'79 911SC Euro

Alright, I've got an opinion on this one.

The O2 sensor on the SC started in the 1980 model year with the addition of the K-Jetronic-Lambda CIS system. The CIS system on the earlier SC is basically the same as this one, except w/o the o2 sensor and fuel pressure modulator on the fuel distributor.

The function of this system (on the CIS engines) was to alter the fuel pressure to lean out the engine to control emmissions (esp at idle). It has little to do with the actual function of the injection system.

Most of these cars with a little wear in the system WILL run much better with it disconnected at no cost to the system's proper function.

They will also run cooler with it disconnected as things are a bit more efficient when the engine is allowed the proper amount of fuel/air that it needs to run steadily at idle and low speeds.

However, the car MAY not pass a smog test with it disconnected. So hook it back up when you go in. In Colorado, we also have a visual check for an o2 sensor present, so I'd leave it in!! Big fines if you are w/o.

THIS IS NOT TRUE FOR LATER ENGINES (ie DME and MOTRONIC, ie 84 and later)

Just my $0.02

Nick.

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Nick Shumaker
1982 911SC Coupe



[This message has been edited by Nickshu (edited 01-12-2001).]

What is your VIN? If it starts with WP0ZZZ then you have a ROW (grey market) car. My 83 ROW did not come with an O2 sensor.

George Wroclawski
83 911SC Cab/Euro

Whether your '80 or later SC has an O2 sensor now, or not, if there is a Bosch control unit under the passenger seat ... you can bet it had a sensor when it left the factoy!!!

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Warren Hall
1973 911S Targa

Hmmm very interesting topic..quick question here though...so is the 02 sensor only working at idle?? I know on American cars it is pretty critical to have a working 02 sensor because it keeps the fuel mixture at 14.7 to 1 (I think)..So this does not apply to our SC's??? If that is the case then do the test pipes they sell help performance??

The O2 works differently on different cars. On new cars, it has a much greater role in regulating mixture. Most new cars would not run well with the O2 diconnected.
On an old CIS car, it was really for fine tuning for emissions purposes only.

The 02 sensor works at idle, as well as at other engine speeds. As far as keeping fuel mix proper, this would be the case for pulsed injection systems such as those on Porsche's after 84, and most all other cars after somewhere around that year.

But NOT for the CIS system.

On the CIS system in the SC and earlier 911's, the fuel/air mix is modulated by the mechanical mechanism in the mixture control box consisting of a venturi which modulates the amount of air entering, and the fuel distributor which alters fuel pressure to adjust the amount of fuel to this amount of air. The 02 sensor added to the CIS in 1980 functions only to further modulate (or lean out) the fuel pressure at idle and at what ever other speed it detects excessive emissions via an electronic valve that can bypass the distributor at a given pressure, and lower this pressure.

On newer Pulsed injection systems, the o2 sensor is a VERY integral part of mixture control because in these systems the computer directly controls mixture AND emissions with input from the o2 sensor, as well as other sensors, rather than the mechanical mech. that is in the CIS system.

Hope this helps!!
Nick.

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Nick Shumaker
1982 911SC Coupe

[This message has been edited by Nickshu (edited 01-13-2001).]

Thanks to everybody for the advice! Does Graham Archers thoughts make sense to folks? It does to me because my overheating problems appeared after my car failed emissions tests. I had a local Porsche independent adjust the engine so that it would pass emissions. After that it passed but started getting hot quick. The dial just steadily progressed up to 250 in about 25 minutes of driving on days above 90. When I took it to another guy he put it on a machine and tested the emissions and everything looked good on the computer but the car still ran hot. He said everything was fine. I’ve taken the intake system off to clean out possible leaves, mouse nests, etc. The upper engine was clean. (Although some mice have now filled up my right side heat exchanger with dog food! I’ve since killed the bastards.) By the way, my cat. converter does not have any brackets to mount an o2 sensor…and my VIN # is WPOAAA so I guess it is not a gray market car. Thanks again to everyone.

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Bruce
1982 SC

The O2 sensor does not mount to a bracket. It is threaded into a fitting, bung, or welded mounting flange near the end. If your cat. does not have an O2 sender mounting, it is most likely a generic replacement!

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Warren Hall
1973 911S Targa

Could it be that you have the "auxillary" muffler or a test pipe?
As stated above, for the '80 on SC CIS system the Lambda loop was an add-on for smog purposes. If your mechanic tuned your car to pass emissions without the sensor in place he tuned it too lean, causing an easy overheat situation. He should have known better than that. I'd think about finding another wrench. At least take it back and have him tweek it richer before damage is done.

[This message has been edited by RarlyL8 (edited 01-14-2001).]

I'd agree with the above. He probably leaned out the mixture control adjustment (to do so you often use the CO reading from an emissions testing device as a guide)--probably just screwing it down until it read favorably. I would go back and have someone set it optimal. I think you can do this using a Bosch CIS fuel pressure tester, rather than the emissions testing equipment. Probably a better measure of the optimal setting at given throttle positions, regardless of emissions.

Best of Luck,
Nick.

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Nick Shumaker
1982 911SC Coupe