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86ragtop
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Oxygen Sensor

When I plug in the oxygen sensor the revs are not stable. When I unplug it the revs increase slightly and are stable. Under all conditions the car seems jerky at low speeds (parking lots/slow moving traffic).
I either have a problem with the oxygen sensor and or the DME.
I figure the oxygen sensor seems the cheaper bet to start with!.
Is there any way to test the oxygen sensor? or is it just a case of replacing it and seeing if the problem is solved!?.
-86 Carrera
PS new fuel pump did the trick for 'dead 911'
now to iron out the other problems!
rgds 86ragtop
Old 11-27-2000, 04:00 PM
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Jim Smolka
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There are ways to test an O2 sensor. However, unless you are @ a factory it is difficult to test them IMHO. For an O2 sensor to start working, the tip of the sensor must be above 300 degrees F.

However, you can buy a cheap Bosch (I recommend Bosch only) O2 sensor for a Ford or similar 3 wire sensor (or 1 wire depending on what type you have) and see if it solves the problem. The connectors are different, so just splice the wires together. There is a good bit of information on a previous post regarding O2 sensors

------------------
Smoke Daddy

[This message has been edited by Jim Smolka (edited 11-27-2000).]
Old 11-27-2000, 04:13 PM
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ewr1
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Jim is correct about using any old 3 wire Bosch O2 sensor. I bought one for a Buick at Pep Boys for 29.95.! Just splice on your connector. One warning - it might not solve the problem...

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E. William Reinecke
1988 Carrera Targa
Old 11-27-2000, 06:24 PM
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stlrj
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My 86 does the same thing when the air flow meter is set too rich, so it probably has nothing to do with your O2 sensor.

But if you wanna know more about that sensor, here it is:
http://mr2.com/TEXT/O2_Sensor.html

Joe
Old 11-27-2000, 06:37 PM
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Early_S_Man
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There is a way to test the O2 sensor ... it requires a digital multimeter, or an oscilloscope to monitor the low-level, DC Voltage signal to the DME control unit after the engine has warmed up. The really dificult part for the owner/mechanic is getting at the wiring to monitor the signal without breaking the circuit to the DME! A breakout box, which fits between the DME and wiring harness ... and gives probe access points to all DME pins, is used in the Bentley test procedure. A high-impedance multimeter or oscilloscope probe MUST be used or the O2 sensor will be destroyed!!! Do not, under any circumstances, use a traditional analog multimeter, and do not short out the sensor lead to ground!!! After engine has run two minutes after startup, and with fully warmed-up engine, the O2 sensor signal should vary between 100 milliVolts, and 900 milliVolts, DC (0.1 to 0.9 Volts DC) as the DME 'controls' the mixture.

------------------
Warren Hall
1973 911S Targa
Old 11-27-2000, 07:40 PM
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86ragtop
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Thanks guys,
I think I will opt for the buick sensor as a cheaper and less technical option. Thanks for the test procedure, but that one is a bit above me (plus i do not have the equipment)
If a cheap sensor does not work I shall try the air flow meter.
i really do appreciate all this help without which my porsche would be sadly sitting by the side of the road!
rgds an appreciative 86ragtop
Old 11-28-2000, 04:01 AM
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stlrj
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The fact that the rpms change when the 02 sensor is disconnected tells me that it's working.

Hey, the sensor I'm using is a 4 wire gizmo out of a Dodge Caravan which I got for free, thanks to our local auto recycler. And the only one who knows the difference is my wallet.

My motto is: if you're experimenting, you better make it cheap because most experiments fail to produce what you want anyway.


Joe
86 Carrera

[This message has been edited by stlrj (edited 11-28-2000).]

[This message has been edited by stlrj (edited 11-28-2000).]

[This message has been edited by stlrj (edited 11-28-2000).]
Old 11-28-2000, 07:40 AM
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I'm having the exact same problem as described by 86ragtop. I 'think' my O2 sensor is working.
Can someone tell me more about the air flow meter? Where is it located and how do I test it or tune it? Thanks much!
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Old 07-30-2007, 04:38 PM
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Here's an excerpt of a previous thread of mine on alternate O2 sensors...that thread got ugly due to a Bosch rep saying some incredible ( technical) things..but this paragraph should still be valid -->

O2 Sensor.. Alert ! ..and new info

--------------------------------------------------------------------------------

Guys:
I've had a lengthy exchange with a rep from Bosch-USA on
the various types of O2 sensors. My primary concern was trying to get
economic alternatives to the very expensive Porsche ( Bosch) units, as well
as understand the various differences that might exist..and also if there
are any caveats. Some interesting things came out of our discussions.
Summary follows:
- the various O2 sensors pretty much act the same way, in terms
of output signal vs input readings, however...
- there are various ceramic types, and for the three-wire
heated systems , various heater strengths ( 12W and 18W)
- for the mid 80's , 3.2L Carrera's, using DME control... you
may substitute:
Bosch 13913, 3 wire unit originally intended for
Ford applications. I believe this has an 8" lead, and you must splice -in
the original Porsche connectors ( more on splicing caveats later).
Bosch 13953, similar 3 wire unit for Fords, but
with ( I believe) 16" long connectors.
Bosch 15725, Bosch "universal" , with universal
connector kit that avoids certain problems compared to using generic
connectors ( again, more later).
Bosch 15726... an alternative to 15725....also OK
to use for 3.2L Carreras.
Bosch 15715, 4 wire .. NOT OK to use ( more on 4
wire later).
By the way , the "long" and "short" Bosch part numbers relate as
follows. The short number ( ex. 15725) is the last 4 digits of the long
number with a "1" in front of it ( long number .... 0258005725 ).

- Wil
Old 07-30-2007, 05:09 PM
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I think I used the 15725 part, and have had no problems with it since installation.
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Old 07-30-2007, 05:17 PM
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"A high-impedance multimeter or oscilloscope probe MUST be used or the O2 sensor will be destroyed!!!"

Not totally correct. Yes the O2 sensor is a high impedence voltage source which
requires a high impedence test instrument, but it won't be damaged by using
a low impedence test instrument or even having its output terminal shorted
to ground.
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Old 07-30-2007, 07:59 PM
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