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-   -   Sensor Question (http://forums.pelicanparts.com/porsche-924-944-968-technical-forum/105391-sensor-question.html)

Roger Hall 04-06-2003 08:55 PM

Sensor Question
 
The green wire is the O2 sensor where it connects to the ECU. The bear coper wire with the black sheild is how Porsche decided to jump the wire from one connector to another. Is there any reason (other than poor wiring or dirty connector) why the copper wire would read less voltage (1/2 to 1/3 less) than the green wire? It doesn't make any sense to me. I think that booth of these wires should read the same voltage from the O2 sensor. Next weekend I am going to connect a new jumper and see if I can correct this problem. I was just hoping that someone would be able to tell me why its set up this way.http://forums.pelicanparts.com/uploads/RogerHall.JPG

todwic 04-06-2003 10:05 PM

Mr. Wilks told me that the outer wire is just shielding. Keeps out EMFs and other nonsenxe. he told me not to hook it to anything.

Roger Hall 04-07-2003 05:57 AM

Quote:

Originally posted by todwic
Mr. Wilks told me that the outer wire is just shielding. Keeps out EMFs and other nonsenxe. he told me not to hook it to anything.
I you are talking about the insulation right? Did you remove your's? Or did you disconect the wire?

I have heard other people talk about the sheilding on other parts of the 02 wiring harness. It just seems a bit of over enginering to me. I admit the O2 signal is not very strong, but did anyone else besides Audi and VW do stuff like this?

awilson40 04-07-2003 10:06 AM

That copper brade is the shielding, It shouldnt read any voltage. When disconnected from the DME its not connected to anything. When plugged in, its shunted to ground. Any yes...most CO's use shielded wire on O2 wire where it might run near an EMF source. This is a very low level signal and you dont want to pick up noise.

Roger Hall 04-07-2003 02:16 PM

Since the O2 sensor gets its ground from the exhaust pipe the signal will remain after the connector is removed. Ground one end of multimeeter to the door stay and mesure the voltage. The reaction in the O2 sensor will continue for a few minutes while it cools off and the exhaust gases disapate.

I doubt that the copper is an EM sheild. The schematic shows the O2 sensor jumped to pin two, and it is not set up as a sheild. It appears that instead of jumping the wire Porsche decided to try this way of splitting the wire to two different connectors.

Thanks for the input.

I am still not sure about this yet its just my .02

Roger Hall 04-07-2003 06:00 PM

I am not knowledgable enough to know if this is correct but here is my best reasoning. Its actually a guess.

When mesuring the frequency valve using a dwell metter I get a steady solid 45 degrees without the O2 sensor conected. This is normal and is the default when the O2 sensor is disconected. With the O2 sensor conected the dwell metter reading fluctuates 42 to 48 degrees. It is causing a fluctuation in the idle. About 50-100 RPM. I can feel it at low speed. Also the air/fuel metter goes leaner than it should. If my guess is correct the signal to the frequency valve is bad. The signal is something like 10 pluses per second. Is it possible that one wire trigers the plus and one wire is conected to the timing circut. Could then the difference between between the two signals confuse the frequency valve?

Roger Hall 04-07-2003 07:47 PM

I rechecked the current flow diagram and I belive you are correct, it is a sheild. Since the conector for the O2 sensor is cracked and falling apart it must be causing a short or allowing interference. Could the interference be causing the fluctuations in the frequency valve? Guess I will have to find a replacement someday. This explains that large plastic connector on the the end of the O2 sensor wire. It must be to sheild the conection.


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