The knock sensor is located under the left rear intake manifold runner for cylinder No. The knock sensor monitors engine vibration caused by detonation.
Basically, a knock sensor converts engine vibration to an electrial signal. When the knock sensor detects a knock in one of the cylinders, it signals the PCM so that the PCM can retard ignition timing accordingly. The knock sensor contains a piezoelectric material, a certain type of piezoresistive crystal, that has the ability to produce a voltage when subjected to a mechanical stress.
The PCM doesn't respond to the knock sensor's input when the engine is idling; it only respons when the engine reaches a spesific speed.
Install the new knock sensor, using the same position the pigtail harness should be at approximately a degree angle to the back of the engine, but using the mark you made is fine as the old sensor. Replacing the knock sensor looks reasonably straight forward but was the engine a twin turbo?
Garage has told me that my knock sensor needs to be replaced and have quoted mega bucks to do the job. They say it's not the cost of the part but the fact that they have to remove so many "bits" before they can get at the sensor. I've trawled through posts on various sites and it does appear that replacing the knock sensor is more difficult on a TT than for a NA car. All you will really need to remove, is the intercooler, its easy to get off Use brute force!
Getting to the sensor isnt easy at all, but it does not require anything else to be removed. Took me and a mechanic mate about an hour to do the whole job. We did have a wireless camera dooberry though, which helped locate it. Then was just a case of removing the old one carefully, and gently popping the new one in the same position. After lots of head sratching and not wanting to undo any water hoses and let air into the heater matirx. I eventually took off the ICV and main intake valve to give me a little bit more room with squeezing pipes out of the way.
I then zip tied a few things and forced them out the way to give me the room to put a spanner on it but only just. The best way for access would have been to remove the black air pipe between the two turbos but this looked very very complicated.
Took ages to get the bolt to rethread as it wanted to go in at an angle, and it's an aluminium head so easy to stip out. This image may help also You can see by this image its impossible to get at that securing bolt without removing a couple of coolant pipes. Socket on a long extension is how I have done this.
Just hold the extension close up against the manifold so you don't burr the bolt. I'm just about to attempt this on my BH5 GTB, but ive found the thread is a little confusing might just be me , do we have a guide how to remove the intercooler? I found when removing mine when it had the standard hard pipes, once everything is loose, brute force is the medicine needed. Gettin them back on can be troublesome too,.
You can post now and register later. If you have an account, sign in now to post with your account. Paste as plain text instead. They are easy to get to. CHECK your oil, these cars use it. Engine Build - Click Here.
I wouldn't be surprised if the hesitation was due to the oxygen sensor Still can't locate the knock sensor, might have to stop by the subaru dealer on monday and ask a technician to point it out to me. I found the knock sensor Just an update Ok, so the knock sensor is located on top of the block towards the back.
It's right under the throttle body. It's visible once you remove the top mount intercooler. After the replacing the knock sensor the engine light has gone away and hasn't come back after a week now. So it looks like a good fixed. How is everyone managing to get this thing out without removing the IM?
I can't seem to be able to wiggle even my wobbly socket over the bolt that holds the sensor to the block without the throttle body getting in the way. The vacation pics say simply to remove the TMIC, and then remove the sensor. Yeah right. I can't comment on the legacy one, but I changed the knock sensor on my 2. I actually had more trouble getting the new one in and threaded than I did getting the old one out. Here's the thread I followed. I also took the advice of some of the responses, and used a 9" extension.
It worked, but I'm pretty sure I broke the damn wrench since it doesn't ratchet anymore. Zoints SEO v2. So you got a P Chances are if your Subaru has over k miles, you're gonna have to deal with this at some point, if it's not the reason you're reading this now. But what the hell is a knock sensor, and where is it, what's wrong with it, and why is it making my engine run like crap?
The knock sensor senses knock. Knock or spark knock, is defined in the automotive world as Detonation. Instead of one combustion, now you have two. This creates a massive pressure spike as the gases expand much more rapidly than intended for the design of an internal combustion engine.
That spike in pressure creates a resonant "shockwave", for lack of a better term, that "rings" throughout the engine and creates a sound most refer to as a "Ping". Any damage and there can and will be damage in certain cases from this "shockwave" will be limited to the cylinder in which it originated, but the noise it creates, the "Ping", which is similar to a hammer strike, will pass through the entire engine, and can be clearly heard outside of the car if the "knock" is bad enough.
This sound is always the same frequency, and so a knock sensor is "tuned", in a way, to "listen" for sounds within a range of frequencies in order to react to knocks and provide data, in the form of an AC voltage wave, for the cars ECU. What causes knock? Octane is a main contributor to engine knock. Octane controls gasolines ability to resist combustion.
Why would you want to resist combustion of gasoline? This is why high compression engines require higher octane fuel In order for the engine to run properly, create as much power, and as few harmful emissions as possible, we need the gasoline to combust at the RIGHT time.
Timing is everything in an engine. Spark timing is wrong, it won't run. Injection timing is wrong, it wont run. Valve timing is wrong, it won't run. Another major contributor to knock is spark timing advance. As the engine spins faster, the time between sparks has to be reduced in order for the spark to occur when the pistons are in the correct position for optimal power production.
The cars ignition system controls this based on inputs from the ECU. The engine spins faster, so the ignition system advances the timing of the spark in order to compensate. The problem is advancing the timing too far will lead to knock under certain conditions.
When the ECU gets a signal from the knock sensor that a knock has occured, it will immediately back off, or retard, the spark timing in order to prevent more knock from occuring and causing severe damage to the engine internals.
What kind of damage? Mostly cracked pistons or broken spark plug electrodes, but in severe cases such as with high HP or forced induction it can be catastrophic fracture of piston crowns, wrist pins, or connecting rods. Cracks in the cylinder head or engine block. Or it can lead to a condition known as pre-ignition.
Which generally is identified after the fact by a hole melted through the center of the piston. Ok, the crash course on knock out of the way, What exactly is wrong with this sensor that it demands my attention to replace? Most of the time, it is corrosion on or inside the sensor that is creating a false voltage reading, or no reading at all. The ECU relies on this sensor to keep the engine healthy, so if it does not receive the signal it expects from the sensor, it concludes that there must be something wrong and it will then set a code, and illuminate the CEL.
However sometimes the sensor can send false data, and the ECU may not catch on right away. It may tell the ECU that knock is occuring when it is not, or that no knock is occuring even when it is. This tends to result in driveability issues ranging from random power surges during acceleration, to misfiring and even stalling of the engine in some cases, even at idle engine speed.
And this can happen even with no CEL, depending the type of failure of the sensor. Subaru Knock sensors look something like this:. Depending on your year and model yours will be similar but the designs did change slightly every few years. The one pictured above fits 95 and 96 EJ Then somewhere around ish the design changed to a type that has a plug directly on the sensor body.
Not sure. It still lives in the same place on your EJ engine though, from all the way up to at least from what I can find. It is hidden below the intake manifold at the rear of the engine. Now that you've found it, you have to have a 10" extension or a few extensions stacked together to get to it.
It has a 12mm bolt holding it to the block. Loosen the bolt, and cram your hand down in there from the back side of the throtle body to fish the sensor out from under all the hoses and wires down there. On later models it helps to remove the air box that is attached to the TB. Unhook the wire connector by fiddling with the locking clip, and you can remove the sensor from the car. What generally goes wrong with this sensor? Most of the time the housing cracks due to heat cycling.
The plastic dries out and splits like this:. Out with the old and in with the new! But wait The section of the sensor housing with the wire sticking out must be turned to the proper angle. Why is this important? Better sensitivity? Lower chance of inteference? Could be any number of things, but the primary reason I beleive is because it won't seat properly and the sensor housing will be damaged if Subaru's instructions are not adhered to.
The area of the block around the sensor is not flat, there is a hump about a half inch away from the sensor mounting boss,and there is a structural ridge in the block towards the bellhousing that can also interfere with the sensor. This area is very difficult to photograph, but I have outline the areas in question in this pic:.
The blue area is the "hump", the red is the ridge, and the green area is the "safe zone" where the sensor housing will not be damaged. Vs one that was installed at the proper angle: looks familiar don't it?
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