Help please changing Knock Sensor on Impreza '94 STi
 

Hi All

I have a 1994 Impreza WRX Sti recently the CEL has been coming on intermittantly and the ECU is reporting code 22 which is the Knock Sensor. The car was recently setup on the rolling road and the garage (Triton Motorsport) did not think there was any issue with knocking but that the Knock Sensor was faulty but they did not have one in stock at the time.

Anyway as its quite a trip to go back to Triton I have ordered the part from main dealer and thought I would have a go at fitting it myself.

My questions are :

1. Where is the knock sensor located ?
2. What is the best way to approach it (from above or below) and does anything need to be removed to access it ?
3. Is an ECU reset required and if so does disconeccting the battery actually achieve this ?
4. Any other tips or advice ?

Any help or advice would me much appreciated.

Many thanks,
Tim

94 Impreza WRX STi
Decat
Dawes Device
283 bhp

buried down on top of the block to the right of the throttle housing, down below the idle speed control valve.
You will need to take the intercooler off to get to it, and even then I think it's a bit of a stretch.

here's a couple of images, the Knock Sensor is No.11.
Don't be fooled by the close up image, as the sensor is buried alot deeper then it looks in the picture.

Attachment 60911

Attachment 60912

Hi Scott T.

Thanks very much for this information - much appreciated.

Anyone else changed this themselves before if so what were your experiences ?

If its buried so far down, is it a pig to get to ?

Cheers,
Tim

12mm socket and a long extension bar to remove it - the bolt has to be torqued to 24Nm when fitting it back.

IIRC that'll get it undone, but you try getting your hand in there to get it out.
Be prepared for scrapped knuckles and wrists.

I found it quite easy mate, hold onto the connecting wire and when the bolt is undone just pull it out, Lineing it back up is a little tricky but not too bad :)

Dave :)

socket and long extention bar and this is an easy job.

Thanks for all the responses - will give it a go today !

Does anybody know if a ECU reset is required after the knock sensor is changed and if so does a battery disconnect achieve this ok ?

thanks again
Tim

Battery Disconnect will do it (30 mins i think)or use the green and black connectors uner the dash to sort it out. Do a search for reseting ECU if you need full instuctions.

Dave :)

Hi, can anyone tell me what does the knock sensor do? and how necessary is it to impreza survival? my 98 sport is showing up the same diagnostics. intermittant CEL and it says knock sensor. thanks for reading!

Knock sensor fault is common on the sport. It just retards the timing when it detects det (pinking) due to low octane fuel etc...

Not as important on a non turbo as it is for a turbo, but still... i wouldnt drive a car with a faulty one.

thank you, musso. the problem is I am not altogether certain my knock sensor is bad. everything was fine until I took into my bog standard gargage for mot and oil change and was ordered a welding job was needed on the drivers side where the plastic body kit is. they did it and I noticed a new bolt fastening the plastic panel to the metal part of the body. pretty much straight after 20 min drive out of the garage was when I first noticed the CEL. yet it was intermittant and taking it back they couldnt do a thing. its not a scooby garage, merely a bog standard place. whatever error, it arose only after they were through with it. I noticed the CEL goes off when I hit 70mph. First I thought the rad coolant was low but I have topped it. I suppose I either buy a new knock sensor or take it into authorised subaru and pay the whack. and no doubt it will be a whack. I am not looking forward to it...

Remove the sensor and clean its mounting. Then tighten it back up.

Also try imprezasport.net
I am sure there is a thread on there about moving the knock sensor so you don't set any false readings.

leaky metal radiator pipe to engine
 

part 2. Found crack on knock sensor, but there's something more sustantial. The metal pipe which runs from the radiator to engine has a hole and has been peeing out fluid. The hole is oblong about 6 mm long. I've tried Quick steel but not much luck. Can anyone suggest a heat resistant metal tape adhesive of some sort?http://www.flickr.com/photos/5842122...in/photostream :wonder:

are you talking about the crossover pipe that sits on top of the engine ? tbh i wouldn't bother trying to repair mate, just replace it. If its got a hole in already i doubt the rest of the pipe will be in great condition

yeah, I think it is. Its metal and painted black, runs from rubber hose of the radiator, bolted down twice over the engine, and has a small arm going left at right angles just under the accelerator mech, while the rest of the pipe heads north to join another rubber hose. But there were so many other pipes and intake manifolds in the way, in the end I chickend out and got ripped off at local subaru dealer. They charged £35 for a second hand waterpipe, which was not exactly in great shape (is this part so difficult to obtain new?) The final bill came to £155, plus shell donax tx dexron III which they informed me was power steering fluid (but I seemed to remember checking the level was fine--unless changing it is recommended after hitting some digits in mileage). Labour was £65. The good news is: after replacing Knock Sensor (£42 from ebay) the CEL is happy. And the cooling seems fine and I cant see any leaks. All in all, this waterpipe is designed badly and it seems the main corrosion area is generally common in this pipe.

http://www.flickr.com/photos/5842122...n/photostream/

There was crack in the old knock sensor. decided to replace it anyway (£42 wasnt so bad). But that's when I noticed a hole, from rust on metal waterpipe across the engine which got bigger and bigger the more I looked.