What Are These Parts?

[ben_t]

The first picture is a socket situated at lower-left side of the engine bay.
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I was looking for the O2 sensor socket location.

The second picture is the same socket with the plug removed.
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As you can see it has 4 pins. So I don't think it is the O2 sensor as it is 3 pin.

The third picture is the plug for the socket.
[attachmentid=20764]

Does anyone know what this socket is for? It looks pretty important.

Does the O2 sensor plug into a socket infront of the cat? I thought it did but I can't find it.

[attachmentid=20768]

One last one. Is this the temp sensor? It has a stray wire leading out from the bottom of it. I thought it might be the ground wire, but I get the temp sensor reading on the OBC so what is it?
It is situated in front of the radiator between the aux fan and the left fog light.
[attachmentid=20769]

Thanks all

[nukeduster]

That 4 prong plug-in is for your fuel rail, if my eyes are not mistaken. You can't really tell where in the engine compartment that connector is located, but the o2 sensor, fuel rail, and ECU diagnostic port all use similar connectors like that one pictured.

By left side, do you mean drivers or passenger side? Are you thinking from a drivers or mechanics point of view?

The outside temp sensor, at least on e30 3 series is located in the left brake ducting.

[ben_t]

The 4 pin plug pictured is situated lower-left side of the engine bay when looking forward from the rear eg. sitting in the seats.

[machinehead]

The external temp sensor on the E34 is, as far as I know, behind the pull out panel next to the left-hand fog light (reference: sitting in looking forwards)- there's where I found the cable when I did my retro-fit of the OBC. It has two wires, your mystery wire seems to be just one?