hernanca

I started this thread after a good amount of searching (relevant threads listed below). I made the subject such that others with this problem could more easily find it among the similar topics competing with it: e.g., that OTHER Green Wire, the O2 sensor itself and associated wiring found mostly OUTSIDE the car.

This thread is about an INTERIOR plastic-encased connector for the O2 signal wire coming from the O2 sensor. This plastic-encased connector is found inside the car, under the CE Panel (you likely have to unbolt the bottom-most part of the CE wood paneling to find it). It takes the O2 signal wire from the O2 sensor and connects it to the fuel computer (in my case, LH 2.2). A green wire goes from the male side of this plastic-encased connector to the computers. The green wire contains a shielding layer not visible from the outside.

If you've handled this interior plastic-encased connector under the CE panel, you, unfortunately, probably know that it has become brittle with age and falls apart and breaks in ones hands. Below is a picture of mine after I tried to pull it apart. The challenge in repairing it is that the green wire attached to it is shielded. As I understand it (I have not taken mine apart), there is a stranded (probably) wire in the middle which is soldered (?) to the male part of the connector, then an insulating layer, then wrapped wire creating an interference shield, then the final (green) insulating layer.

I can't help but wonder if they aren't all brittle now. I could not find a part number for the male side of this connector (with the green wire coming out of it) in PET, but the Sensor side options, containing the female side of the connector, are as follows:

911 606 123 00 (80-, Oxygen Sensor; US 78-82 PET; M157 option?)

928 606 124 00 (Oxygen Sensor; US 83-86 PET; no M157 description)
928 606 128 00 (Oxygen Sensor, heated; US 83-86 PET; no M157 descript.)

928 606 128 01 (Oxygen Sensor, heated; US 87-91 PET; M157 option?)
928 606 128 01 (Oxygen Sensor, heated; US 92-95 PET; M157 option?)

For those of us who have had (or will have) this connector fall apart in our hands, I have the following questions to the electronic and chemical folks:

1. Does the plastic surround matter? It seems separate from the wire "shielding" which is part of the green wire. Do I need to worry that the plastic surround is now compromised?

2. Can I just use something like Super Glue/Krazy Glue to put it back together and seal it back up (if it matters), or maybe wrap it with electrical tape? I believe epoxy is petroleum based, would that be OK to use for this connector to the O2 signal wire?

3. If I DO find an intact green wire with a good male connector at the end of it, how difficult is it to swap the whole thing out? It looks like the green wire traces back to both the EZ-F and the LH computers. (Thanks to Alan's fine primer for me even being able to figure that out!)

4. Are all 928 Green Wires a potential PITA? (rhetorical )

5. What is the shielded green wire shielding? I am assuming it has to do with the intense maze of wiring in and around the CE panel, since from this connector to the O2 sensor itself, there is no shielding. Is there a different way to provide this shielding?

6. What would be an ideal solution to fixing this brittle connector which I suspect we all now have? I don't want to buy a whole new harness just for this wire and connector. Finding a used green wire with the male connector attached is like finding hen's teeth. Splicing a shielded wire (the green wire) is a PITA to do right, and you still need to find a non broken plastic connector to splice in.

Related threads (I will link some of these to here, as appropriate):


A. Ladybug83's fix (splicing):
https://rennlist.com/forums/928-foru...ug-repair.html

B. Another thread. Some talk of solutions in this one. I believe there is some confusion however about which wiring side of the plastic encased connector we are talking about:
1) the "Sensor side" signal wire (from the sensor in the exhaust, then through the floor/tunnel grommet and ending at the female end of the brittle connector in question)
vs.
2) the "CE Panel side" wire (shielded green wire from male end of brittle connector in question up into the computers:
https://rennlist.com/forums/928-foru...lded-wire.html

C. Closeup of what an intact connector looks like in CoachTom's 86.5:
https://rennlist.com/forums/928-foru...ese-wires.html

D. Topic not directly related, but contains good pics of an intact connector and description of associated wiring (for heating the O2 sensor) on another 86.5:
https://rennlist.com/forums/928-foru...computers.html

E. JobeJoe's 1980 L-Jet car:
https://rennlist.com/forums/928-foru...or-really.html

F. Warning not to solder the OUTSIDE 02 sensor wiring, found in 944 forum:
https://rennlist.com/forums/944-turb...r-wires-2.html

G. Warning about using Silicon anywhere it can get to O2 sensor:
https://rennlist.com/forums/928-foru...o2-sensor.html

H. Another warning about Silicon anywhere near O2 sensor:
https://rennlist.com/forums/928-foru...e-to-find.html

hernanca

OK, so with my new "skills" of being able to better read wiring diagrams, I traced the O2 sensor wiring using the factory workshop manual (FWM) wiring diagrams for the 1986 model year. The Model Year 1985 looks exactly the same for the O2 sensor wiring. 1987 is slightly different with the green shielded being replaced by a white shielded wire instead. And 1984 is more different and does not tell me what color the shielded wire is (though pictures from a 1980 model seem to show it as being green).

On my car (1986.5) the brittle plastic barrel connector of interest is only used for the O2 signal - nothing else. This is likely also true for 1985 and early 1986). (On my car,) there is one black wire for the O2 signal coming in from the O2 sensor to the female side of the barrel connector and one shielded green wire coming out from the male side of the barrel connector and going to the LH 2.2 (pin 20), among other things. The brittle barrel connector is represented by the male/female connection point shown right at the symbol for the Oxygen Sensor (But the connector's male/female is opposite of what is implied in the wiring diagram: male side goes to computers, female side goes to O2 sensor - see diagrams, below).

The marked diagram below shows the trace of the green wire (marked with green). The german word "Schirm" seems to mean "shield" because the 1985 wiring diagram says "Shield" in the same spot that the 1986 diagram says "Schirm". That green wire shielding is shown connecting to three brown wires, and so the shielding is grounded, as has been suggested! One of these brown wires goes to pin 11 on the LH computer, another goes to what looks like the low octane wires on the EZ-F computer, and the third goes to the common ground point MP IX. (See diagrams)

Also coming from the O2 sensor, in addition to the signal wire, are two more wires for cars so equipped (I don't know if this was always an option). One is brown and the other one is BLUE (Edit: had previously misread diagram as indicating black). I believe one or both of these wires are used for heating the O2 sensor (aka, the "three wire O2 sensor"). On my car, these two wires also come in through the tunnel/floorboard grommet, but then have their own separate destinations once inside the car:

1. The BLUE wire (I marked with yellow) goes to the fuel pump relay XX (which I suspect is what triggers the O2 heater to come on).

2. The brown wire (I marked with red) goes to common ground point VIII (MP VIII).

According to Alan's (928 electron wrangler) electrics primer, brown is usually unswitched ground for 87+ cars. From the 1986 workshop manual wiring diagrams, this looks to be the convention for the 1985 and 1986 Model Years as well.

The shielded wire is grounded in the 1984-1987 wiring diagrams I looked at, but in different ways. In the 1984 and 1987 diagrams, the shielding is grounded by simply being connected to an appropriate pin next to the pin where it connects to the control module (The LH in 1985-1987).

I am curious to see how the shielding is connected to the brown wires! Anyone have pictures?

I would also be curious to see what the 87+ (brittle?) plastic connectors look like.

Randy V

Yo, Carlos - what up, dawg?

Smoke any good cigars lately?

M. Requin

Nice job on those diagrams- very easy to follow.

hernanca

Randy, how did you guess!? I had to type the above v-e-r-y carefully - I kept brushing the screen with my column of ash!

Thank you, M. I took a cell phone picture of the diagram then used Microsoft Paint. I figured if I was going to go through the trouble of tracing it, I might as well save the effort!

John Speake

Hi Carlos the 87 and later O2 connectors don't go brittle and they are a hard rubber material.

They are Dura seal connectors.

hernanca

Thank you, John. Very good to know. So it seems, these brittle connectors are only a malady for 1980-1986.5 cars with catalytic converters. (I am not sure if non-cat cars have Oxygen (O2) sensors as well).

I could not find an O2 sensor in the 1979 wiring diagram, but maybe it's there and I just couldn't find it!

Attached are some pictures taken from other threads. The first three are of the intact 86.5 signal wire connector and the separate O2 heater wires connector. They all look like correct 86.5 wire colors for the wires going to the computer (green signal wire containing shielding), fuel pump relay (blue wire), and ground points (brown wire) inside the car. The last one I believe is the Dura seal connector for 87-95 cars which John indicates and which connect all three wires using just this one connector (last pic is from one of Wayne's tutorials on an '87 car).

hernanca

I could not find a good picture showing the wiring orientation on the pre-87 O2 heater connectors so I wanted to create my own. The 86.5 automatic wiring is a bit hacked, so I went to the 5-speed and found what I needed.

iklln6

I hate being that guy that resurrects a thread 8 years young, but I have a PhD in mechanical engineering with concentration in sensor design and robotics...and can maybe help tie off this loose end at the end of the thread thread with the mystery of the shielding being at one end only. No I do not know Mr Porsche or his official design rationale here - this is a literal educated guess.

Short answer: the shielding exists only where there is a source of interference known by design - the area with all the other signals and noisy power lines converging at the connector. Outside there are no significant sources of interference (at least, none in the 944 designs) for that particular signal line (likely high impedance as mentioned earlier, but not THAT high).

Expanded discussion: Shielding is intended here to be a shield between the signal and sources of interference. It's nice to have shielding grounded, but not completely necessary (it can still offer beneficial shielding by just existing as a floating conductor, it just may build up a small charge). Best practices nowadays would likely require a couple pages of explanation as to why it wasn't used despite the Holy word blessed upon us by IEEE, and that hassle would be incentive enough for a modern engineer to just design in a grounding point, albeit an unnecessary waste of materials and manufacturing steps, ultimately costing over a million dollars' worth of materials labor and time over the production life of the car and repair parts for decades following; drawing a line on a blueprint/computer screen is less work for the engineer than writing a properly formatted couple of pages explaining why it's unnecessary, and the lifetime cost is unquantifiable. And this, ladies and gentlemen, is how 'best practices' policies destroy the planet. F* best practices policies without simple ways to deviate that properly allow the engineer to create the best design for the project when the generic company-wide best practices policies won't/don't.

This minimally and seemingly nonsensically-shielded cable is a throwback of a bygone era when engineering had a different purpose than it does today: to create a good product, not a simple product.

That said, is this a good design? It's good enough. It's effective enough for its purpose and no more. Extending the shielding to the cat with it grounded at both ends would have required another grounding point at the cat-end which may or may not have required additional design elements. May have introduced safety issues. May have been its own source of interference if the ground itself is noisy. I don't know enough about the 944 or the catalytic converter or the mechanical area to speculate on how simple or complicated the situation would have been in grounding the outside end. I'm just assuming it would have been trivial to ground at either side and that the ground is a clean path for absorbed EM radiation converted to electrical charge to discharge and that the choice to shield the whole thing would have resulted in no more or less effort relative to the choice not to shield the whole thing thus not a factor and the decision was solely based on what was necessary and no more.

hernanca

Hey, killn6 - Thank You!!

Not because I was waiting for an answer these past 8 years, but because I had forgotten this is where I documented this O2 sensor information, which I will need soon enough when I start to Sharktune my 86.5 Automatic 928!

Good to know that the ground point for the shielded wire may not be absolutely required also!