QwkTrip

iTrader: (23)

I'm wiring 2-wire knock sensors into aftermarket EFI. Anybody know what is the polarity at the sensor connector? I can't figure out which side is Signal vs. Ground.

ddnspider

iTrader: (26)

Many are not polarity sensitive. Some are so measure between the boss and each pin. If either pin has continuity to the boss then that's your ground pin.

QwkTrip

iTrader: (23)

That's a slick idea. Thanks!

QwkTrip

iTrader: (23)

There is no continuity between the pins or to the case. But I found the answer here, https://www.lsenginediy.com/sensors-inputs-guide/ , and then found pictures of which pin has which color wire.

This is also an interesting article for people that want to know more about how it works. http://www.wellsve.com/sft503/counterp_v12_i2_2008.pdf

ddnspider

iTrader: (26)

I'd like to know the guts of those flat response sensors. If they aren't tied to the boss, it seems like you should be able to wire them either way.

grubinski

You don't really know what's in the black box. It may well be a circuit that expects the polarity of applied voltage across it to be in a particular direction, even if it's not directly tied to chassis ground at that pin. There may be other stuff between that pin and ground that's inside the PCM. The sensor is only part of the circuit.

BBPanel

iTrader: (4)

So if one uses one of the flat response KS with a P01 PCM is there anything to do other than specify the type of sensor in the bin?

ddnspider

iTrader: (26)

pretty sure they're piezoelectric sensor...so there's not an entire circuit in them.

QwkTrip

iTrader: (23)

It is. It's explained in the wellsve article I posted earlier.

The strategy and hardware are different.

* Looks like the strategy portion is available to you in the software. (Check that box off. )
* You would need to add a ground wire back to ECM to complete the hardware portion. I don't know if the ECM has a ground pin assigned for that function or not.

I did the switch using Holley HP EFI. In that case both Gen III and Gen IV knock sensors use the same +5V reference wire, but I had to plumb in a Ground reference wire for the Gen IV knock sensor and select the correct strategy in the software.

BBPanel

iTrader: (4)

The S&P harness I have has a 2-wire pigtail (lt blu, dk blu) for the ks - if it required a ground I'd think it would have been included. Where on the sensor would a ground go?

QwkTrip

iTrader: (23)

Judging by the wire colors, I think those are the two 5V wires that go to the two 1-wire knock sensor that are typically mounted in the valley of the engine block.

If you want to change over to the 2-wire knock sensor mounted in the sides of the block then you reuse those wires and add extra wires for the ground back to ECM.

With my Holley HP EFI I tied the ground into the same common ground that all the sensors use. I don't know what you need to do for your particular ECM. You'll need to figure that out.

BBPanel

iTrader: (4)

No, the pigtail is a single 2-wire piece and the ks is also.

QwkTrip

iTrader: (23)

That's not the connector that plugs into the knock sensor. It's just a plug where you're expected to finish the harness to knock sensors.

The answer is right there in the picture you posted. Those are the two signal wires that go to the two 1-wire knock sensors, one for left hand and one for right hand. You need to buy or make your own sub-harness to the knock sensors

BBPanel

iTrader: (4)

Ok, I see now what you are saying - guess I'm having a senior moment. I even tried connecting the harness plug to the sensor and it doesn't work. I found these two pigtails:
https://www.eficonnection.com/home/product/knock-detonation-sensor-2-wire-flat-response-ls2-ls3-ls7-connector-pigtail for GM LS2 LS3 LS7 Gen IV 58x LS-Series Knock Sensors but discussion says 24x also
https://www.eficonnection.com/home/p...nector-pigtail for GM 2001-2005 4.3L Vortec engines
Looks like I have the LS2-3-7 ks - but both have a blue wire and a gray wire - so I'm guessing the gray is the ground you spoke of. Your suggestion to connect to the sensor common ground is probably correct - I hadn't noticed a common ground on the pinout table - I'll have to review again. Thanks for pointing out the errors of my thought process.