'73 w/3.2, o2 sensor?

[E Sully]

I installed an '86 3.2 in my '73.5. The wiring harness that was supplied with the engine seems to be from a federalized car. It has no o2 wiring. Instead it had one of those boxes that are hacked into the wiring. The engine and DME are US models. I removed the offending box and repaired the wiring harness to stock.
I finished breaking in the engine after a top end rebuild. It runs great, pulls hard and clean to redline, no oil leakage, not a hint of smoke on startup. Compression test shows 185lbs on all cylinders. Plugs look good.
I am using backdated '73 SSI's into a Bursch turbo muffler. I would like to add an o2 sensor back into the system. Any suggestions on where to weld the o2 bung on the SSI's? Also, I dont' know how the Carrera's o2 sensor heating circuit works. It appears that I would just tie it in to the DME relay accoring to the wiring diagrams, but I see that a separate relay, 821-951-253-M14, is listed for 1980-89 cars. There is no sign of it in the wiring diagrams. Is it used in the 3.2's?

[Dantilla]

My 1973.5 coupe is powered by a 1987 3.2.

The O2 sensor is located on the driver's side SSI, just aft the 3-into-1 collector

[jlpintl]

I have a 77 911 that has an '84 3.2 with the 3 wire oxygen sensor located as described and yes, I have been over the wiring diagrams and cannot find where to locate the oxygen sensor relay. I've looked under both seats, in the engine compartment and in the trunk. If you find out where to locate it...I'd like to know.

I replaced the oxygen sensor not more that 20,000 miles ago just as a routine maintenance item but now there is a light on my instrument panel (with no lens) that is glowing - it is just above and between the tach and speedo. I was told it is probably an oxygen sensor warning light but the lense was missing when I bought this vehicle. It has never lit up except when starting like all the warning lights do so I never paid much attention to it.

I read somewhere else that it is possible that this light will come on if the relay is bad but the sensor can still be OK and that it's more common than one would expect so I bought a relay - 0 332 019 150(it costs 10 times less) so I thought I'd try that first since the Oxygen sensor is supposed to last at least 60,000 miles. I know, I could have got some contaminated fuel or something and will go ahead and replace the sensor if I can't locate this relay. I guess it's possible that the guys who built this car up never installed the relay and just went straight into the DME or there is not even supposed to be a relay even though it shows up at the parts store lookup but cannot be found in the wiring diagrams.

[E Sully]

I found this regarding your light. Seems as though the counter for your cars original o2 sensor needs to be reset every 30,000 mi. I found the relay in an '80 SC wiring diagram.
Do you know where your oxygen sensor is grounded? Any chance you might have a picture of the DME and relay wiring for the motronic?

[jlpintl]

Thanks Sully, Someone else had suggested the "counter reset" method you suggest but with no specific instructions as you have provided...now I'll have to figure out how to remove the speedo but that's what I'll try next.

The car runs great so I really doubt there is a problem with my O2 sensor.

There is nothing under the passenger seat except for a "pansonic" box that seems to be wired into the sound system. No relays or such. I think my O2 sensor is just wired directly into the DME with no relay at all. That's kinda what the wiring diagram I have indicates. I took a picture of the DME control unit, DME relay and altitude correction box under my driver's seat and will attach the picture for you. You can see the blue tape where the relay is connected into the harness.

Also, I looked into the engine compartment where the three wires come up from the o2 sensor and they plug into a cable (part of the harness) that appears to be heading into the cockpit seemingly towards that DME located under the drivers seat.

In my wiring diagrams, in the Bently service manual for the Carrera it shows the 1984 ground distribution for the O2 sensor to the "ground engine" as are the 5 grounds coming out of the DME (10, 5, 16, 17, 19) , the ground from the altitude correction box and DME control unit relay.

[jlpintl]

I will have to send three replies to include all the pics

[jlpintl]

As you can see by the tattered "under seat" this is a 77 vehicle :-)

[E Sully]

Originally Posted by jlpintl

As you can see by the tattered "under seat" this is a 77 vehicle :-)

All Porsches are beautiful, and they all have something else that could be "fixed".
Thanks for the info. The items that you don't have under the passenger seat are I believe for the 80's lambda system for their o2 sensing system.
I guess I'll just run 2 wires to hook up to the dme relay for the heating circuit, and the DME connector for the o2 signal, and a ground in the engine compartment.
Thanks Jlpintl