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Discussion Starter #1
Can someone confirm I have the picture below labeled correctly and that I have indeed located the O2 sensor output wire and the associated wire going to the ECU? My wiring diagrams don't have it labeled well.

Thanks!
 

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On my '85 it is a thick green wire. In your picture, at 1 O'clock from the inertia switch there is a Bosch connector. That is probably for the heater wires to the O2 sensor. Trace them back - down, and you should find a single thick wire running with them. That is the signal wire from the sensor.
 

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No, I do not believe that is it. That looks more like the brake pad low sensor line. The O2 sensor is only up to 1v so has to be shielded. Green line as mentioned before. Should look like this: (The Bosch connector is for heating it up) green line is signal.
O2 sensor wire.JPG

Pull the boot apart and there should be a spade connector in there.
 

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Well, now I know why it hasn't been easy to locate the O2 output wire….it's not there. Traced back to the O2 sensor itself and there is no 3rd wire. All that is there is Bosch connector with the 2 wires. Explains how I mistakenly did this: http://www.alfabb.com/bb/forums/alfetta-gtv6-1972-1986/389090-part-fuel-injection-system-did-i-kill.html. Luckily I got off easy with some blown fuses.

I am guessing that a PO installed an earlier model O2 sensor in there, as I think those only had 2 wires. Will the 2-wire O2 sensor even operate in a later model designed for the 3-wire? That 3rd wire, the green one, is what carries the actual signal back to the ECU, right?

Seems the wires are still in the engine bay…just tucked off to the side (see pic). I have a few such disconnected wires as the PO removed the A/C. I just assumed these were some of them, but looks like not.

So do I need to get a proper 3-wire O2 sensor, or can I make this 2-wire one work?
 

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I think that the two wire sensor has one wire for signal and one for signal ground. Presumably there is a color code? The signal wire should go to your green wire and the signal ground should go to ground. You will have no heater which means that it will take longer to start working after the engine has started from cold. The corrrect sensors are not expensive.
 

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Discussion Starter #6
Unfortunately Alfa didn't call out the wire colors for the O2 sensor on the schematic (see pic below). But looking at the schematic it seems to me that the 2 wires (marked as dashed/shared on the connection) going to connector 23 in the ECU are probably the sensor heater wires. And the 1 wire going to 24 is likely the signal wire.

Sound right?
 

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I have a schematic of the BMW L-Jetronic CPU and from it it looks like 23 is the lambda sensor signal input and 24 is 12 volts but in the Alfa Spider Bosch manual 24 is the signal and 23 is the shield. I think that your diagram is like the Spider. In any case, the green wire going through the firewall is the signal.
 

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Discussion Starter #8
Well if it's green, then I'm not getting a signal. Which would explain (hopefully) why I am failing smog (which is where this all started). Hopefully running rich for however long it has been hasn't killed the cat, too.

Thanks for the help. I thought my smog fails were O2 sensor related from the beginning, but after I shorted/surged the circuit when trying to test it, I got spooked and decided to do everything else first (air leaks, timing, plugs/cap/rotor, etc.). Not a bad thing…car is new to me in the past couple years and now I know everything is nicely tuned. ;-)
 

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If you have a voltmeter set it to DC volts and measure between the two wires from the sensor with the engine running. If you see a small voltage, less than 1 volt that varies as you get on and off the gas then the sensor is working and the wire that is positive is the signal wire.

If you want to spend some money and have some fun then buy a Zeitronix ZT-3. There is an output wire to connect to our CPU in place of the existing sensor and you will have an AFR readout of what the engine is doing.
 

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Sorry if I am jumping in later to this string, but how is this different from the 82 GTV6? The PO did some hack job on the wires of this car, which I am still straightening out! One thing he cut free was a dash indicator for EXH Sensor. When I plugged it in, it lights up and won't shut off. Also the O2 sensor is a single wire one and was not connected. I did find the Green wire which I was told is for the O2 sensor, but I have not dug in too deep on this one since the other projects are my main focus. I have a new single wire O2 sensor to install, but I am guessing this car may need a 3 wire given these clues.
 

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Discussion Starter #11
An 82, as coming from the factory, had a 2-wire O2 sensor. The 3rd wire was on later models (starting 84, I think) and provides an electric heat source to the O2 sensor so that is will start operating more quickly rather. Earlier models didn't have this and instead relied on the exhaust heat to power the O2 sensor.
 

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Discussion Starter #12
Ed-

That's a cool diag tool. And not really much more $$ than the OEM Bosch sensor. And it fits in where the existing O2 sensor goes without any mechanical adaptation needed?
 

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That's a cool diag tool. And not really much more $$ than the OEM Bosch sensor. And it fits in where the existing O2 sensor goes without any mechanical adaptation needed?
It fits in place of the existing sensor. You have to run the supplied cable to the "black box". Mine is under the glove compartment. Then you have to supply switched 12v and GND to the box. I picked up the 12 volts that was for the heater of the old sensor. You could pick it up from the combo relay.
 

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There are times when you need a wiring diagram and there are times that you do not. This is one of those times that you do not.

Unfortunately Alfa didn't call out the wire colors for the O2 sensor on the schematic (see pic below).
Uh, you were told it is green. Why are you concerned with the wiring at the ECU? It's pretty clear some genius clipped the O2 sensor wire and tied it off at the fender.

What you need to do is get under the vehicle, drop the exhaust by disconnecting some exhaust hangar donuts, locate the O2 sensor forward of the cat but before the downpipes. See if wire has been clipped totally (if so, replace O2 sensor - get unit with proper pigtail for 3-wire [also, you may need special Alfa tool to remove collar]), if not, and the O2 sensor has a wire harness going up towards the firewall, give it a yank. If it falls to the ground you have just located the O2 sensor wires. If not, trace to where it is probably tied-off.

What Ed was saying was that THIS part of the wire is where you can test for voltage coming off the O2 sensor (iz what they do). If you get 0-1v and/or oscillating voltage bouncing back and forth, after engine is warm, then your O2 sensor is working. But I wouldn't bet my lunch-money on it.

From your first pic it appears that your heating element is intact and I would gamble that your signal wire to ECU is as well. I would advise you stay away from the harness and the ECU.
 

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Discussion Starter #15
Yep - have already done that. Actually, it looks like someone installed the earlier model O2 sensor because the one currently installed only ever had 2 wires. There's just enough mystery under my hood that a properly marked diagram would just remove some guesswork with the various other disconnected wires (from the removed A/C) and the fact that I've never seen one of these wires in its proper form before so not 100% sure what I was looking for. Alfa marked the color of pretty much every wire BUT this one in the diagram, which indicates to me that it could be a color besides green. Ultimately the green seems to be it.

At any rate, help here is appreciated. Even in the best circumstances I'm no electrician, so making this as variable free as possible improves chances for success.

Thanks!
 

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Since the signal wire (grn) is disconnected and tied-off at the fender, I wonder what the PO connected this 2-wire O2 sensor to?

My guess would be the heating element. You can see from your first pic where it is circled here in white.
02.jpg

Remove 2-wire or whatever they have installed. Order the proper 3-wire unit which will look like this:
3-wire O2 Sensor.jpg

Run pigtail up firewall, keeping distance from exhaust manifold. Connect Bosch connector to lead I circled and thin Black wire with boot to green input wire - which hard to say because of the electical tape on it but it may still have the proper (tan) connector on it like in my first pic..

Move-on to next issue.
 

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Discussion Starter #17
Yep, the PO connected it to the heater wires (the Bosch connector). Wonder if that in itself would fry the sensor? Doesn't much matter because I am going to either re-install OEM or the gauged sensor that Ed posted.

I, however, don't think that green wire in my picture is the sensor wire after all. I traced it back into the main wiring harness at the firewall which terminates in the fusebox. I think if it were the sensor wire it would go into the ECU. So the green wire may actually be one of the old A/C wires after all.

I am cleaning up all the grounds in the L-Jet system, which will lead me into the ECU anyway. So when I am in there I'll take a look and see if I can locate the sensor wire from that side. As far as I can tell, it was snipped.

It's an otherwise well-sorted car, but this will take a bit of noodling to get figured out.

Thanks for the help.
 

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Discussion Starter #18 (Edited)
Seek and ye shall find (below)…traced from the fuel injection wiring harness and found it stuffed up under the dash.

Thanks for everyone's help. If you all hadn't shown me what I was looking for it would've been much harder to find…and would've easily mistaken the green disconnected A/C wire (from my previous pics) for the O2 sensor wire.

Mystery solved…and hopefully my smog test woes as well.
 

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