Hey guys-
I have almost everything hooked and ready to try and start the motor for the first time. I have a one unknown plug and one unknown sensor here they are.
First picture is the sensor, located right in front of the bell housing.
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The second picture is a brown, two pin plug.
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Thanks guys!

and I apologize for the grammatical errors in the above post.

you might want to identify what eng/fi we are talking about

My Bad!!! 1998 2.5 Subaru engine, using stock ECU

Real men dont wear gloves...

No idea about scooby plugs...

Rich

Trust me, if my dad didn't get them for free (he works at Stanford hospital) then I wouldn't use them. I think each box is about $20!!!!


Now back to the plugs.... anyone?

I looked at a manual for a 98 Legacy GT w/ 2.5L DOHC engine so I am not sure if it matches the engine you have.
The sensor you are showing is the knock sensor and should be plugged into a gray 2 pin connector.

The location diagram I have lists two brown 2 pin connectors, 1 for the coolant temp sensor and 1 for the EGR solenoid. If you can tell us the specific model your engine came from I can look and see if the list different connectors.

Jim

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from looking at that diagram it looks to be the EGR pin connector. I am pretty sure the EGR solenoid is a valve that is used to put fuel back into the fuel rail if it is unused during combustion.


And I did source my harness after I got the engine so I have an unused plug on the wiring harness that I think is for the knock sensor. It is the only single wire plug on the harness. And the knock sensor has a single wire plug as well. Do you think I can just clip the plugs off and make my own connection?

-Peter

Peter,
I would not be cutting any connectors off and wiring until I knew for sure with out a doubt I was connecting the correct component to the correct circuit in the harness. You got the harness separate from the engine, did you get the ECU with the harness or with the engine? There can be significant differences between an ECU and harness use in 1 model compared to the same engine in a different model. I am far from a Suby expert but I am very familiar with the subtle differences between similar engine control systems. In 1992 Audi installed 4 different ECU's running 2 different control programs in the same model car with the same engine.
I think you need make sure your ECU matches your harness and then get a wiring diagram that matches the ECU/Harness and make sure the engine is set up the same. If you have a sensor on the engine that does not match the harness connector it may not work with the ECU. I have never seen a knock sensor with a single wire, all I have seen have a ground shield that is part of the sensor and harness and connectors.

EGR is Exhaust Gas Recirculation, it is an emissions system used to drop combustion chamber temps by dump exhaust into you intake. Since exhaust won't burn and is now part of you air fuel charge you get less fuel and air and lower temperatures, also less power. If you engine does not have EGR you need to make sure the ECU you have is not expecting EGR or it will probably set a fault code and typically reduce power out put to protect the engine.

The new engine control systems are so sensitive sometimes it can be very difficult to get mismatched components to work together.

I can probably help with a wiring diagram if you can determine what year and model you need.

Good Luck

Jim

Jim-
Thank you for this information. When I bought the harness, I did buy the corresponding ECU from the same car. I then sent my harness to the guy at enginewiring.com who did the re-working of the harness to outfit it to correct the signals and run only the engine. I got the harness back but it was missing the actually engine harness (the plugs that plug into the EGR sensor, fuel injectors, temperature, camshaft...etc). So, after about a month and a half of trying to call this guy, who's voicemail was full, I never got in contact with him. It kinda felt like his business went under. So, I went back to the original company I got the harness from and ordered just the engine harness from them. This is where I am now. Do I have too many different wiring harnesses going on? I really appreciate any help, I have been very worried about the wiring from day 1. And now my worst fears are setting in. I'll try and do some research and figure out what year engine, and harness I have. Although I am almost 100% positive that it is a 1998 wiring harness and ECU. Which makes me think I may have a different engine than I thought.

-Peter

So, I went searching through the 1996 manual I have. Here's what I got. It looks as if the knock sensor is a single pin connector on the earlier models. however... it says it is a grey single pin connector but the knock sensor coming from the engine and the knock sensor on the harness are both white, single pin connectors, and look like they should fit together, but are of course slightly different.

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-Peter

how bout this...

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...
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You can probably verify the ECU you have by the part number on it, then find the diagram that goes with it. If you get a wiring diagrams you can trace the wires from the pins at the ECU connector to the to the sensor/switch/etc on the engine and make sure all is connected correct. I would probably try to find a new knock sensor that has the correct connector before I would splice the wiring because the connectors don't match. Or I might modify the connector if I though I could make it work as a test.
Maybe the company you got the harness from could provide some info on the knock sensor connector.

Good Luck
Jim