Ash Webster

Can someone with a v3 sti show me their knock sensor wiring from the knock sensor and also coming from the ECU... Trying to figure out how /why /where the shielded wire is grounded, if the knock sensor is 1 wire output amongst other stuff!

Big thanks in advance!

Don Clark

If it's anything like the UK MY97 the shielding is not actually connected at the sensor connection but has it's own connection pin where the wiring passes from the engine loom ( connector E1) to the main bulkhead loom ( connector B20) on the RHS (drivers side) of the engine. The shielded wire then runs with others into the cabin and the shield is separately terminated (from it's ECU connection) at a 22 pole shield joint connector (B83) next to the ECU. A number of these 22 connections connect to other wire shields and engine sensors and to the ECU providing a route to earth.

Basically the shield only has to be connected at one end to be effective.

Ash Webster

thanks don - appreciate your time.

how would you advise (an electrician) to rewire it?

remove the sensor wire fully (yellow wire), and then find where the shield wire goes into the B83 connection. i just need to figure out which of the connections into the b83 and b20 is the ground (shield) wire no?

the reason im asking this is im getting constant knock readings even when the knock sensor wire into pin 4 is cut!

am i on the right wavelength?

Don Clark

B83 connects to ECU B136 pin13.

AFAIK (my best guess)
Being single wired, the early OEM knock sensor itself, earths via its mounting bolt/mounting face on the block. The shield of the loom cable is just there to protect against stray electrical signals (noise) whilst in close proximity to other wires in the wiring looms.

Later models have a 2 wire knock sensor , the second wire being part of a common sensor 0v to the ECU

The ECU, from the ECU pinout, appears to require a "carrier" signal of 2.8V at pin 4 (assuming the pin out is the sames as a UK MY97) and should always have 0v at pin 13.

Knock is detected by the piezo electric effect mV generated/detected above the 2.8v threshold. I would think that if pin 4 is disconnected then you'll get knock all the time as it is basically at 0v.

MY97 UK turbo pinout page 2

1509joe

iTrader: (2)

Don iirc the earth is the shield as well cause it goes right into the sensor. I seem to remember working on a classic with a broken shield and it threw a knock sensor code.

Don Clark

If the shield went to the sensor the connector would need to be double pole which it isn't. It's not shown as such in any wiring diagrams.

If the shield became disconnected from earth then it would not be doing its job of shielding the signal cable so yes you could get "noise" producing knock symptons.

1509joe

iTrader: (2)

Looking at that picture you must be right in what your saying but could you tell me what year wiring diagram that is cause I have a notion the v5 and v6 changed to two wire !!!

Ash Webster

thanks for the info !! massive help i can show this to the auto elec (unfortunately booked up until next Sat but luckily i can drive without a knock sensor). The car has been plagued with false knock sensor codes for years it will genuinely be a massive relief to finally be able to run it how it should be.]

Final questions as i think im actually clued up on this now! - what is J, and b4 on the pictures?

(i found a page which tells me the colour codes of the wiring etc, LW = blue / white, sb = shielded outer)

Don Clark

Wiring diagrams are for MY97/98 (v3/v4)

As previously mentioned

b4 is pin 4 on connector B136 of the ECU
J (in the octogon) is the link wire from the shield to the Joint connector which goes across two pages of the wiring diagram.

Download this below and read the first section and keep for reference - It's for a MY01 but the basic diagnostic section is universal.

http://ken-gilbert.com/wrx/01impreza/imp01_wir_1.pdf

Should by some chance the screen from the sensor does actually cross the first connector and is used as the return feed, then you should be looking at whether the plug/socket has any corrosion in it (The red part shown in the photos is the waterproof seal).
Similarly where the Engine loom connects to the Main loom and where the main loom connects to ECU and Shield joint connector.

Ash Webster

thats the one i found the wiring colour codes on

thanks again. now i just have to be patient and wait a week :/

1509joe

iTrader: (2)

That would add up ok as I pretty sure the car I was working at was a v5 type r and the outer sheath was broken/disconnected as some one had tried to fit an unknown year sensor to it