How can an SC run w/o an OXS system?

[Dogbreath]

I am discovering even more crazy things that the PO has done to my 1982 911SC.
I was trying to track down where some loose wires belonged and confirm the functionality of CIS system.

Some things I have found...the OXS Control Unit had no power from the fuse panel.
The O2 sensor is not connected. The WU relay had no power.

I am not sure how the car can be running at all.
How is it possible that the car can start and run with the OXS system disconnected or did they use some type of bypass to fool the CIS into thinking the O2 sensor was there?

Even after I attached power to the OXS Control Unit and replaced the relay, removing it has no affect on the idle of the car.
There are times when I start the car after 5 minutes of very hard cold start it will run and idle flawlessly, other times it runs very rough and idles very poorly.

Does anyone have any suggestions about where to start. I assume I need to get the OS sensor re-wired and connected and then confirm that I have power to the Frequency Valve, WUR and Cold Start valve.

Thanks

[tirwin]

My understanding is that the O2 sensor is unique to US models -- it was required to meet U.S. emissions standards, so ROW models didn't have it. That says to me that it's not required to make the car function.

When the O2 sensor is disconnected it has the effect of running continuously in open-loop.

The net effect is you won't get as good gas mileage with it disconnected.

I would like to hear more discussion about pros/cons. The PO disconnected mine and it seems to be fine. He believed the car runs better with it disconnected.

[kjchristopher]

They start and drive with the system disconnected. You just have to adjust the meter to get the mixture right. But, you won't get fuel enrichment without the computer, as it uses the flutter valve to enrichen. The O2 sensor itself is only used part throttle, and its absence won't shut the computer down.

Some people unhook the O2 sensor. Personally, I run it.

[psalt]

I would start by hooking up a dwell meter to the test port and diagnosing the system. Sounds like you have a failed FV and the PO has bodged the system. The Lambda CIS 911SC will run without the OXS ECU, but the fuel curve will be incorrect in many places and you cannot expect anything like OEM drivability without it. Most people with no knowledge of the system do not understand the difference between a disconnected/failed O2 sensor and a closed FV. The K Basic part of the system is calibrated way too lean and the FV needs to be pulsing at the default values for the fuel curve to be anywhere near correct. If the dwell meter shows no pulsing, you need to test the FV and the ECU.

[javadog]

One mistake people make is assuming that all CIS cars are largely the same. The fact is that Porsche made changes to the design of the system each year, and an '82 is quite a bit different than an '80, for example. An O2 sensor may not be required to make an SC run properly, if you also change all of the other related components. The assumption that some people make that A ROW car is largely the same, excepting the O2 sensor, is wrong.

The best way to learn how these cars work is to study the service training documentation that Porsche provided to the dealers each year, that described all of the changes that were implemented since the prior year. You can find these booklets on eBay if you watch carefully.

I'd definitely hook up the O2 system on an '82 snd fix all the other issues that are probably present.

JR

[tirwin]

One mistake people make is assuming that all CIS cars are largely the same. The fact is that Porsche made changes to the design of the system each year, and an '82 is quite a bit different than an '80, for example. An O2 sensor may not be required to make an SC run properly, if you also change all of the other related components. The assumption that some people make that A ROW car is largely the same, excepting the O2 sensor, is wrong.

If I remember correctly, the primary differences between US and ROW models are about 3 or 4 things: O2, cat, decel valve and I can't remember the other(s). What are the other differences?

In regards to the OP's question I was merely trying to point out that Porsche seems to have designed the car without an O2 sensor, so technically it is not required (and the point about the other differences that go along with no O2 is a good one).

The OP asked a good question. But sometimes statements made on this forum are nothing more than folklore -- repeat it enough times and it must be true, right? And it's really hard to tell the difference sometimes.

I certainly don't want to be guilty of that. I'm just another poor owner who loves trying to wrench on his car trying to figure things out.

[javadog]

Regarding the fuel system, when a CIS car has an O2 sensor, there are also several other components that are different. The fuel distributor is the first one that comes to mind. Then there's the airflow sensor, control pressure regulator, etc. Ususally, these components were different between cars with and without O2 sensors. You almost have to go year by year to chart the changes, as there were so many of them. In addition, ROW cars of that era had different pistons, cylinder heads, intake pipes, cam timing and other things. Generally, starting in 1980, ROW cars had more compression, larger intake ports, etc. The cam timing had two different settings and both the US and ROW cars used each of the settings at one point or another, often though they were different in a given year. Then there were things like the pre-muffler used in place of the cat and differences in the minor details like the ignition timing, or vacuum limiting valves, evaporative emissions plumbing, etc.

JR

[psalt]

In regards to the OP's question I was merely trying to point out that Porsche seems to have designed the car without an O2 sensor, so technically it is not required (and the point about the other differences that go along with no O2 is a good one).


This is a bad assumption. The US 1982 911 SC was in fact designed with an O2 sensor. The ROW engine was designed to run with a constant lower chamber pressure. The US engine was designed to run with a variable lower chamber pressure which is how it accomplishes the fuel mixture trim.

[javadog]

Yeah, you can run without an O2 sensor, if the rest of the system is changed, too (or at least several of the major pieces). And, a US car will run with the O2 sensor unplugged. It won't run as well as it did with the sensor plugged in, and everything adjusted correctly, but it will run. It's also easier to do this with an early car ('80, '81) than a later car ('82, '83) because of some of the detail differences in the CIS systems.

There are a lot of these cars now that run poorly, because of owner's "re-engineering them", or failing to fix them when they break, and even by well-meaning shops screwing them up by fixing them improperly. There are guys that know these systems well but there are also guys that should never get near one. I've seen a lot of components that are disconnected, or plugged off, wrong control presure regulators or fuel distributors fitted, etc.

I think most people are far better off leaving them alone and keeping them stock. If you were into 911's when these were new cars and got to drive them when they were fresh off of the boat, you'd remember that they drove really well, if they were adjusted properly.

Y'all have fun,
JR

[tirwin]

Thanks for correcting me. As I said, it is sometimes hard to know what to believe.

[Dogbreath]

I think I have the WUR and the AAR sorted out and now I was thinking about putting the deleted O2 (OXS) sensor back in my car. It appears that the PO replaced the catalytic converter with one that did not have a connection for the O2 sensor.
Has anyone put the O2 sensor back onto a catalytic converter? Can I just drill a hole in the Cat and weld a nut over the hole and screw the sensor into it or is there more to it than that?
I bought another wire harness so I can probably run the O2 sensor wire directly back to the OXS Control unit. I just need to figure out how to get the O2 sensor back into the equation.
Thanks

[Kraftwerk]

Is the '83 OXY sensor is somehow connected to the odometer? Light goes on after a certain number of miles, it seems is that possible? coincidence?

[spuggy]

Originally Posted by Kraftwerk

Is the '83 OXY sensor is somehow connected to the odometer? Light goes on after a certain number of miles, it seems is that possible? coincidence?

On the '77, the EGR warning light is run by a counter box behind the instruments in the dash that the transmission sensor pulse goes through. Once this counts enough pulses, it lights up the bulb as a reminder. There's a reset button on the side...

[mikesride]

My 82 SC Has back dated exhaust with ssi's, no cat and no O2 sensor. Adjusted mixture and idle and she runs better than before....that being said what do the experts suggest I should further change out?

[Jesset100]

Originally Posted by spuggy

On the '77, the EGR warning light is run by a counter box behind the instruments in the dash that the transmission sensor pulse goes through. Once this counts enough pulses, it lights up the bulb as a reminder. There's a reset button on the side...

So, where is the reset button?

[James Brown]

Originally Posted by spuggy

On the '77, the EGR warning light is run by a counter box behind the instruments in the dash that the transmission sensor pulse goes through. Once this counts enough pulses, it lights up the bulb as a reminder. There's a reset button on the side...

behind the tach, pull ti out

[Jesset100]

My mistake was thinking the big white thing was the button. Well, moving some of the wires around is when I saw the little white button in the lower right corner. The button is recessed so using a chopstick is the easiest was to push it in.