O2 sensor wire

[mih0001]

This is a strange thing that I ran into. I was trying to replace the O2 sensor on in my 84 944 and while tracing the wiring i found that the black wire did not have a complete connection (see picture) Someone at one time tried to solder this piece back together, but one wire comes in (black) and two exit just like a coaxial cable one inside the other. Does anyone know if this piece has to be there? or can i just attach the black wire to the interior green wire? It looks important , in the middle where it is broken it looks almost like a thermocouple of some kind. Appreciate any help, these forums are incredible.

[NKN84944]

I was just tackling this job today myself. I am confused by your picture though, what exactly are we looking at? I just bought the universal and was going to splice into the black line right by where the oxygen sensor screws in, but found out I don't have the right size wrench. Do you know what size it is (I am guessing maybe a 21mm or so)?

As far as soldering a connection on the oxygen sensor line, I heard it should never be done as it alters the reading. Only crimp connectors should be used (my universal came with one fitted onto the small output wire of the sensor).

[mih0001]

the peice is located here on the firewall when it hasnt been removed by me (red arrow) on the right is a green wire that is a wire within a wire (blue arrow), on the left side is the black wire that comes directly from the o2 sensor (blue arrow). somehow in this piece located above, a one wire input is changed into two wires. any ideas?

[tooter884]

The green wire consists of an inner standed conductor, which is insulated, and an external braided shield. This wire goes to the DME. The braided shield is grounded at the DME; therefore, no connection is required on this end. Cut the braided shield back about 1/2 inch from the end of the green wire insulation so that it does not contact the inner stranded conductor. The black wire coming from the Oxgen Sensor is a single insulated stranded conductor without the shield. A connection must be made between the green and black stranded conductors. DO NOT solder these wires. The Oxygen Sensor uses the air gap in the stranded wires to draw clean air to the Sensor. The solder can plug these air gaps and adversely affect Sensor operation. The original DME/Oxygen Sensor connection at the firewall location was made using a male plug (DME side) to a female socket (Oxgen Sensor side, the one with the black rubber boot). If either of your connectors is broken or missing, then you should CRIMP the two wires using a crimp connector or connectors (male and female) of your choice. A removable connection here is not necessary, but is convenient if the DME/Oxygen Sensor path requires troubleshooting in the future.

[mih0001]

thanks tooter, that really helps.

[mih0001]

tooter, I had one more question for you or anyone else reading this board. I purchased a bosche universal o2 sensor from autozone that has one wire on it. However, the o2 sensor on the car has 3 wires. Do i need to purchase a 3 wire sensor from pelican? or can i use this 1 wire 02 sensor and just leave the two white wires unhooked?

[bryanthompson]

My bad, I was mistaken.

[tooter884]

You will need the three wire version. This version, installed on later model Porsches, has one wire for the signal voltage to the DME, and the other two provide a DC voltage for an internal heater in the Oxygen Sensor. The heater enables the Sensor to come up to operational temperature near immediately. The one wire Sensor does not have a heater, and the Sensor is out of the DME loop until the exhaust heats the Sensor to operational temperature. Go to Clarks Garage site at the following link to learn all you need to know about the Oxygen Sensor [http://clarks-garage.com/shop-manual/fuel-18.htm]

[nize]

you must use the 3-wires!

make sure you use the correct universal sensor;
http://frwilk.com/early944/misc/oxygen.htm

and;
http://www.clarks-garage.com/shop-manual/fuel-18.htm

[jchill]

Went to change the O2 sensor in my 87 924s this weekend and hit a snag. The sensor that was installed wasnt even plugged in. After hunting around I found an unused wiring harness attached to a loose bracket that looks like it should be bolted onto the back of the engine.

Anyway the plug from the sensor has two wide 'female' pins for the heater I assume, then a single 'male' pin for the sensor voltage. This random harness I found has three thin 'male' pins.

Haven't had a chance to dig further for perhaps another harness. Any ideas on how I can determine if this random harness should actually have the o2 sensor connected?

I will be able to get photos tomorrow.

Thanks!

[nize]

the o2 sensor harness is located at the back of the intake manifold. it is the only round harness in that area. if you are missing the half that connects to the sensor, you might have to buy the porsche factory one as that is the only way i know of to get the correct plug.

[jchill]

Thanks nize, that's where I expected it to be but the bracket was empty. After digging around I finally found the correct harness down back near the exhaust manifold. Plugged in the old sensor and tried it out... doesn't seem like its burning as much fuel but its still rich, also sluggish and slower throttle response. Thing needs to be replaced anyway.

The weird thing is this... I thought it was coincidence at first when the buzzer for the key-left-in-ignition or headlights-left-on stopped working when I plugged the sensor in. Unplugged it, and the buzzer is back. I'm hoping the new sensor will fix it, not looking forward to tracking down a weird electrical problem.