Knock sensor plug missing from harness

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Hoff2015
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Joined: Sun May 24, 2020 5:27 am
Car: 1990 Nissan 300zx TT

Knock sensor plug missing from harness

Postby Hoff2015 » Wed Nov 25, 2020 6:55 am

I bought a 1990 na to tt conversion and found that the knock sensor was disconnected. I can’t seem to find where it plugs into the harness. I’ve checked the fsm and there doesn’t seem to be a extra plug where the knock subharness is supposed to plug into. I found a layout on concept z performance for their replacement harness that shows it in a different location than the fsm, but neither place has an extra plug. All of the plugs on the harness are accounted for. I thought about running an extra wire directly from where the knock sensor connects to the ecu and connecting the knock sensor in directly. Anybody else experience this?


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NolimitZ32
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Car: 91 AG2 2+0 TTMT swap/E39 BMW 540i6/E53 4.6is Dinan S3
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Re: Knock sensor plug missing from harness

Postby NolimitZ32 » Mon Nov 30, 2020 10:13 am

Knock sensor needs a shielded signal IIRC so if you do run your own make sure its the correct type of wire. The knock harness connector can fall behind the engine, also it runs from one of the side bundles (again IIRC). if you can trace where it's supposed to come from you may be able to find it or at least find where it may have been cut.

Hoff2015
Posts: 13
Joined: Sun May 24, 2020 5:27 am
Car: 1990 Nissan 300zx TT

Re: Knock sensor plug missing from harness

Postby Hoff2015 » Mon Nov 30, 2020 12:27 pm

Thanks for the reply. I have the engine out of the car and I’ve been up and down that wiring harness. Without completely stripping the covering I just can’t seem to find where the wire is cut. Whoever did the swap did a piss poor job and just didn’t have the knock sensor connected. So if I’m splicing into where it plugs into the ecu at the 23rd spot on the harness, I’m guessing that since the ecu is receiving a signal from the knock sensor, the other wire going to the sensor is 12v?

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VStar650CL
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2004 Nissan Altima 2.5 S

Re: Knock sensor plug missing from harness

Postby VStar650CL » Mon Nov 30, 2020 12:30 pm

No, for knock sensors just signal and a shield ground. The sensors are piezo, so they generate their own voltage.

itsa300zx
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Car: 1990 300zx NA W/TT swap
2011 Nissan Rouge S
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Re: Knock sensor plug missing from harness

Postby itsa300zx » Mon Nov 30, 2020 2:06 pm

Image

Look at middle of the pic, DET sensor is next to the blue Air regulator plug.

Note: the VTC plug looks exactly the same as the DET plug.

Hoff2015
Posts: 13
Joined: Sun May 24, 2020 5:27 am
Car: 1990 Nissan 300zx TT

Re: Knock sensor plug missing from harness

Postby Hoff2015 » Mon Nov 30, 2020 2:47 pm

Yeah I’ve seen this diagram before. It’s simply missing from the harness. I think I just have an odd harness. The wire where it connects to the ecu is supposed to be white but mine is light brown.

Hoff2015
Posts: 13
Joined: Sun May 24, 2020 5:27 am
Car: 1990 Nissan 300zx TT

Re: Knock sensor plug missing from harness

Postby Hoff2015 » Mon Nov 30, 2020 11:08 pm

OMG I just figured it out. The stupid POS who did the swap on this car had the plug for the detonation sensor going to the driver side VTC. I wonder if they ever got this car running right. :crazy:

itsa300zx
Posts: 1142
Joined: Sun May 31, 2009 9:39 am
Car: 1990 300zx NA W/TT swap
2011 Nissan Rouge S
2002 Acura MDX
Location: up North, Edm. AB

Re: Knock sensor plug missing from harness

Postby itsa300zx » Tue Dec 01, 2020 7:32 am

Lol, glad to hear. Actually pretty common mistake since both connectors are the same and same location.
So, are you missing a drivers side VTC connector then?

Hoff2015
Posts: 13
Joined: Sun May 24, 2020 5:27 am
Car: 1990 Nissan 300zx TT

Re: Knock sensor plug missing from harness

Postby Hoff2015 » Tue Dec 01, 2020 7:46 am

There is a cut wire on that part of the harness which I thought was like the egr temp sensor or something. I tested the continuity with where the VTC is on the ecu harness and it turns out that’s what it is. I labeled all the connections on the harness as I was taking the motor out of the car. You just assume that everything is correct. Lol
Thanks everybody for your help.


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