O2 Sensor question……..

[schubee]

I was working on my car this weekend and I noticed my O2 sensor was not hooked up. Hmmmmm.....what to do, I hooked it back up and took it for a spin. Prior to this, the car was running excellent. Now, I’m noticing a surge when driving in low gears around 2500 – 3500 rpm’s. It kind of hesitates, hard to describe. It’s not as smooth as it was before, it’s like the timing is off or plugs are miss firing. When I unhooked it, everything is fine. Is this an indication that my sensor is bad? Thanks in advance for your comments.

One more Q: Do you disconnect the O2 sensor when you do a timing?

Forgot to mention, when down shifting, I'm experiencing excessive back firing whereas before I wasn't.


------------------
John
'81SC Targa

[This message has been edited by schubee (edited 08-05-2001).]

[Jamey]

John, my '82SC had an annoying rpm occillation at idle. At the advice of many on this board, I disconnected the O2 sensor. RPM's are a steady 900 now and the car performs great. Perhaps yours was disconnected for similar reasons.

[N11Porsche]

Let's see: the car ran perfect before you connected the O2 sensor back up. Now it runs poorly. My suggestion would be to disconnect it again and don't worry about it.





------------------
Bill Carcot
1979 911SC
Diablo Region, P.C.A.

[pwm74]

i would invest in a new one, then try it.
prior owner disconnected it because it was the reason,maybe.

[Jim Smolka]

I remember a similar post regarding a disconnected O2 sensor. Turned out, the reason for the disconnect was to mask a faulty Fuel Injector.

[mm86911]

I had teh same situation with my 86 (autothority mass air meter/chip) and find that the car idles and revs much better with the sensor disconnected.

[twin plugged targa]

mm86911, I have heard many SC owners state that their car can run fine without the O2 sensor hooked up.
However the post '84 Carreras are a different 'kettle of fish'.
Here you are dealing with the DME-Motronics system where, when you inplug the O2 sensor the whole system runs far too rich.
In our system, unplugging the O2 sensor masks the problem and does not solve the problem.
This is fine for the short term, but if you really want your car running at optimum performance - Plug it in!.
Ageing electronic cars can be a pain to get running right, due to the mutlitude of electric connections any one of which can go bad and send bad info back to the DME brain send your system out of whack!.
I have recently found that after weeks of trouble shooting my car with an ignition problem that the car once running was still not perfect- revs oscillating.
This was cured by cleaning the O2 sensor and adjusting the CO screw to lean out the engine.
Incedently I found the best setting to be 7 turns out (factory is rich at 5 turns).
I know this was an SC related thread but I would not want Carrera owners to start de tuning their cars on the basis of what is right for SC's.
Hope this helps
Rgds Ben

[nhromyak]

I am under the impression, from reading Bruce Anderson's articles both in Performance Handbook and Excellence, that disconnecting the O2 sensor can cause the engine to run a little more rich, usually with better power and a little smoother acceleration. However, Bruce goes on to specify how the '84 - '89 3.2s suffer from valve guide wear when the cars were running rich. Apparently, too much fuel in the combustion chamber has washed away the oil on the valve guides, possibly causing premature valve guide wear. Hence, I am running mine WITH the O2.

I have noticed with O2 sensor disconnected;
MORE fuel consumption,
NO power gain,
Better steady idle at 850 RPMS.

with O2 sensor connected;
surging on acceleration,
better Gas Mileage,
little lower IDLE ~800 RPMS (sometimes fluctuating when hot).

I have a chip and recently removed my Catalytic converter, which SEEMS plugged, hoever no performance gain with CAT removed.

If I were you, I would have my CO percentage checked, and have the engine put on a computer diagnostic machine (BEAR or SUN diags). You could go to the local community college with an automotive department and have them run some tests, usually for free!
These computer diags can tell you if you might have a weak ignition, fuel injector or low compression cylinder.

Good luck, Have FUN!

------------------
Nick Hromyak
'85 Carrera 7 & 9 Fuchs
Havin' Fun in Sacramento

[gslater]

John -

When I dropped the engine out of my '80 SC last fall, I noticed that my O2 sensor was disconnected (wire was broken, probably unknown to previously owner, who then had someone adjust the mixture and such because the car wasn't running well). After putting the engine back in, I fixed the wire and reconnected it to the sensor. The car ran VERY rich after that, and kind of screwy as far as idle speeds and such were concerned. Probably because other adjustments had been made after the wire broke long ago. I read up on O2 sensors, learned how to test mine, and decided mine was bad. Bought a $25 (or so) generic replacement at Pep Boys, and all was well again after a slight idle speed adjustment.

My point in all this? I think that anyone who reconnects their not-worn-out O2 sensor and then has running problems has some other problem besides the O2 sensor. Since the purpose of a normally functioning O2 sensor and corresponding computer is to "fine tune" the mixture ratio, I have a hard time seeing how having the sensor connected can be a bad thing, unless you're trying to optimize the mixture one way or the other.

[Early_S_Man]

There are several links to O2 sensor information in the following thread:
http://www.pelicanparts.com/ultimate/Forum3/HTML/011757.html

------------------
Warren Hall
1973 911S Targa

Over rich mixtures = death to catalytic convertors.
Before removing O2 (Lambda) sensors take the time to read one of the following booklets that cover the injection systems as used by Porsche.

Bosch has several technical instruction booklets covering the different injection systems.
1. Motronic Engine Management
2. ME-Motronic Engine Management
3. Gasoline Fuel-Injection System K-Jetronic
All around $15.00 plus shipping from
www.bentlypublishers.com or from Pelicans book section

Bosch also has other books covering other areas of automotive systems. And the Automotive Handbook which is about 900 pages of reference.
Also there is a book by Charles O. Probst
"How to understand, service and modify Bosch fuel injection & engine management"
from Robert Bentley Publishers
Just a thought
Chris

[This message has been edited by cwood (edited 08-06-2001).]

[Superman]

The O2 sensor is part of a system that gets the engine to run REALLY LEAN. With everything working properly, disconnecting the O2 sensor has the effect of subtly improving idle and driveability, including the subtle surging you report. I made the very same observations on my car and my O2 sensor stays unplugged now.

I'd agree that a richer mixture can tax, or plug, a CAT. My CAT has been, ahem, 'ported,' so plugging it is no longer a worry at all. Happy motoring.

------------------
'83 SC