85projectZ28

I have a question as to where the wire should go from the O2 sensor. I have a 1985 Z28 5.0 TPI automatic. I had someone do my headers a few years ago and (long story short, car doesn't run now). So I just recently looked around and saw that the O2 sensor is in the driver side header towards the very end, bout 4 inches away. The wire is coming out and going up to the connecting part, but from there on... Nothing!!! Its like they forgot to plug it in on the other end! But I can't find any wire anywhere to plug it in to?!?!?!? Did they cut it off??? I know it should be a purple wire but I cant find it. Where does it run along back to the ECM? Does it go under the tranny and up on the passenger side to the ECM? Or does it go straight up from the exhaust on the driver side and then around back to the ECM? Or what else??? PLEASE HELP!

rough

Its a purple wire, and should be looped with a green wire which is the temp sensor, and purple go into the ECM while the green branches off to the gauge.

Sounds like maybe there was a narrowband 02 on there at some point and they never reconnected the sensor, or your buddy cut it, and let the other part that connects to the ecm get sucked into the wire harness, which goes over the top of the trans.

85projectZ28

Still cant find it. Got any pics of how that wire runs?

Sickboy_84

I'm having the same problem I can't find where it goes a picture would be the best way if anybody has one I looked in a Haynes manual but those pics suck

rough

A picture still wont help ya, you just locate the O2 sensor, and follow back the wire, it will be tied with 1-2 other wires, so you might have to split those looms to continue to follow it. It should chase down the the passengers side firewall where it enters and goes to the ecm

85projectZ28

ya a pic would help actually. the senser is not connected to anything! a wire comes out of the sensor and then just ends. it must have been cut off but i dont know where. i think i am going to have to work reverse and just trace the wire from the ecm to the point where it was cut. but that is going to be a mission and a half!

fervernt

I literally JUST(within the last 2 hrs) found this wire. The coolant temp sender that runs the gauge is located between the 1 & 3 cylinders, and has a green wire plugged into it. follow that wire into its loom. it will meet up with a second purple wire. this is your o2 sensor wire. if it's not there then idk lol. but it looks like it stays in the same loom for awhile so I would follow the green one for a bit and see if it meets up with the purple one anywhere. Hope this helps. Believe me I would have loved to have this info. my o2 sensor is literally on the wrong side of the engine, but has a wire plugged into it..? I don't know how the P.O. effed this up so bad, but it's just one of a looong list of problems my car has. took me a month to find the right wire because I didn't know it was on the other side of the engine.

85projectZ28

Awesome! I'm going to look there next time I get a chance. There's no other purple wires in that loom that I could get it confused with is there? And one last question... Can I disconnect the wiring harness entirely at the point where it enters the inside of the vehicle from the passenger side fender???

fervernt

as far as the wiring harness disconnecting, I have no idea. Never had to try it. And as far as I know there are no other purple wires that go into that loom. doesn't seem very likely. gm may not be the brightest people in the world, but I think they would be smart enough not to put 2 purple wires in there that close together. If you do find more than one, post it up here and I'll see if I can help identify it more. just keep in mind I'll probably be learning right along with you. I've tried to avoid wiring as much as possible lol. I hate it.

85projectZ28

ok so i looked and I'm not too sure if i found it or not. i took a couple pics. i followed the green wire that was attached to the temp sensor between spark plug 1 and 3 and followed it back to its main loom. no purple wire but there is a thicker pink wire which runs along without a break in it. i did find a purple wire a little further down but it is not running towards the ecm. it runs towards the plug in box thingy that connects to the firewall on the drivers side?!? I don't see why the O2 sensor would need to run through there. Plus, i cut the wires to my wiper motor since i took out that whole assembly, and I'm pretty sure that those wires were the ones to the wiper, so I'm not too sure if thats the purple wire I'm looking for... refer to the pics for the spots I'm talking about...

fervernt

at the bottom of the first pic, there's a small loom with a green and what looks like a purple wire. I think that might be it. am I correct in thinking that green wire goes to your temp gauge sender? if it does, that should be the right one. If you have access to it, use a digital volt ohmmeter and probe the wire. I believe you want to probe with red, and ground the black one to the body. If it's the o2 wire, it should have ~.5 volts to it. Do a search if possible and verify that voltage number because I'm not positive.

85projectZ28

ok the green wire in the first pic thats sitting on my thumb is the one that goes to the temp sensor. the other two green ones were to the a/c compressor which i no longer have, which is why they are cut. but i noticed that the green wire goes into that harness on the driver side, just the same as the purple wire i found does. so maybe thats it. i can't check for voltage because my car is stripped. no engine, no battery, no nada. but i will check for continuity when i get my tester back from my dad. I'm just gonna place one end in that wire and the other end in the wire that comes out from the ecm which i know is the O2 sensor wire. i will post the findings in a couple weeks or so when i get my tester back.

fervernt

alright keep posting when you get more info. I'm interested in what you find, but I'm about to the limits of my knowledge now. I'm hoping someone else might chime in for a sec and confirm everything

ASE doc

Since the vehicle is dismantled, one sure way to verify the O2 circuit is to locate it at the ECM connector and, with the ECM disconnected from the harness, use an ohmmeter to perform a continuity test between the corresponding terminal of the ECM connector and the cut purple wire in your harness. This way you will know that you have the correct circuit. Of course, never use an ohmmeter on a connected ECU as the trace voltage from the ohmmeter can potentially damage the ECU. However, it is standard practice to perform continuity checks on a disconnected harness.

All Data shows the O2 circuit as being pin D7 of ECM connector C2. If you look closely at the connector, you can read the numbers.

Jules Hamel

I have the same problem on 5.7 . did you find the connector. 1987 iroc z

Jimvbob

can i please ask, will i run into problems if i dont use the 02 sensor wire, it is not connected and i am installing headers, tks