Knock sensor replacement 97 2.5

[ThosL]

I saw a youtube video, but was not clear with all the dark and a few discernable parts of the engine.  I took off the throttle body cover but could not find it.  Anyone have a clear picture of where this is? Thanks.

[idosubaru]

2 hours ago, ThosL said:

I saw a youtube video, but was not clear with all the dark and a few discernable parts of the engine.  I took off the throttle body cover but could not find it.  Anyone have a clear picture of where this is? Thanks.

It’s super easy. 

Have a good flashlight handy.
To the drivers side of the throttle body, straight down, the only thing with a 12mm bolt facing straight up.  
 

there are zillions of FSMs for free that show it and people have posted the image countless times. 

[idosubaru]

Found these, first search, took 30 seconds:

https://images.app.goo.gl/rWRZ1Zx73dhzDwJv5

https://images.app.goo.gl/c5EhBsFre8x9bBN1A

Edited October 12, 2020 by idosubaru

[ThosL]

It was relatively easy on a 2.2 EJ22 due to better access.

 

This one on an EJ25 was a royal pain!  #1 access is highly problematic.  If the plug on the old unit won't pull apart you will have big problems as the core unit could get damaged.  If you get it apart, and then access the bolt with an extended access ratchet, you still have a lot of problems left.  So presuming you are able to pull the bolt up, you still have to align the new knock sensor correctly.  Then you have to lower the ratchet with extender and bolt correctly through the sensor donut at just the right position through the mounting hole.  I used tape to keep the bolt in the ratchet extender, still it fell out and there is no way to reach it with your hands unless you have fingers like a child.  All in all an underrated job better left to mechanics.  As the do it yourselfer may not have the right tools to do it.

[idosubaru]

9 hours ago, ThosL said:

It was relatively easy on a 2.2 EJ22 due to better access.

 

This one on an EJ25 was a royal pain!  #1 access is highly problematic.  If the plug on the old unit won't pull apart you will have big problems as the core unit could get damaged.  If you get it apart, and then access the bolt with an extended access ratchet, you still have a lot of problems left.  So presuming you are able to pull the bolt up, you still have to align the new knock sensor correctly.  Then you have to lower the ratchet with extender and bolt correctly through the sensor donut at just the right position through the mounting hole.  I used tape to keep the bolt in the ratchet extender, still it fell out and there is no way to reach it with your hands unless you have fingers like a child.  All in all an underrated job better left to mechanics.  As the do it yourselfer may not have the right tools to do it.

Yep, You’re right. I was answering your question about location - it’s easy to find.  

 for replacement the dohc EJ25 is far more cramped than an EJ22.  disconnecting the ancient plug can be tricky, dropping something down there is a time sucker. 

[ThosL]

What tools make this job easier?  Also does the orientation and torque matter that much?  Why did this unit come about in the development of the engine? Is it a necessary part of most engines? Are there any tell tale signs of a failed knock sensor?

[Rampage]

Link to the FSM just for the knock sensor. Scroll down for the 2.5. Torque spec is very important.

http://jdmfsm.info/Auto/Japan/Subaru/Legacy_Outback/1997/Service Manual/ENGINE SECTION/FUEL INJECTION SYSTEM/MSA5TCD97L3521.pdf

Orientation-- Mainly wire length. One of our EJ 22 had a ridge on the block where the wire comes out of the knock sensor and caused it to crack the plastic housing on it. I turned it towards the Left headlight.

If the engine begins to knock (low octane gas) it will send a signal to the ECU and it will retard the timing.

The ECU needs to see it is connected, otherwise it will set a code.

The knock sensor can retard the timing soo far that the engine will die and not set a code.

[1 Lucky Texan]

^^^^^ that, good post.

[ThosL]

I'd point out that a lot of these knock off units are coming from China, may not be quality, not sure.  Just check ebay, units are around ten bucks delivered.  Went to Auto Zone yesterday to find the code and sure enough knock sensor still.  So I checked the connection and made sure the connection was good, car ran better.  I disconnected the cables later to reset the code and now the car has zero juice even with jump cables connected.  Will start another thread on that.

[nipper]

1 hour ago, ThosL said:

I'd point out that a lot of these knock off units are coming from China, may not be quality, not sure.  Just check ebay, units are around ten bucks delivered.  Went to Auto Zone yesterday to find the code and sure enough knock sensor still.  So I checked the connection and made sure the connection was good, car ran better.  I disconnected the cables later to reset the code and now the car has zero juice even with jump cables connected.  Will start another thread on that.

The harder the part is to get to, the better off you are getting an OE part from a subaru supplier.

[ThosL]

Would always pay a reasonable premium for an OE.  Auto Zone quoted over $90 for a knock sensor they were selling!

[nipper]

5 minutes ago, ThosL said:

Would always pay a reasonable premium for an OE.  Auto Zone quoted over $90 for a knock sensor they were selling!

Sheesh online Subaru dealers list it as 72.95

[nipper]

Also keep in mind OE has lasted this long odds are OE replacement will last just as long

[ThosL]

2 hours ago, nipper said:

Sheesh online Subaru dealers list it as 72.95

I have nearly 280K on the car, makes no sense to pay crazy money on this one as OE units should be a lot more reasonable than that.

[nipper]

Look used then as personally I would get oe even at that mileage

[ThosL]

CEL went out, so I will monitor the timing related issues which the knock sensor seems to affect.  

[ThosL]

There are plenty of OEs on ebay, etc. for under $20 delivered.  https://www.ebay.com/itm/22060-AA061-New-Front-Knock-Sensor-for-Subaru-Legacy-Forester-Impreza-2-2-2-5L/402339281418?_trkparms=aid%3D1110006%26algo%3DHOMESPLICE.SIM%26ao%3D1%26asc%3D20140131123730%26meid%3D8036857877cb4ae8aee917033980a4d3%26pid%3D100167%26rk%3D3%26rkt%3D15%26sd%3D192926413511%26itm%3D402339281418%26pmt%3D1%26noa%3D1%26pg%3D5411%26algv%3DDefaultOrganic%26brand%3DUnbranded&_trksid=p5411.c100167.m2940

 

It makes no sense to pay $50 plus as Auto Zone quoted me, plus the unit I got is working at this point.

[ThosL]

Also many of the OE parts on cars from the 1990s, etc. are gathering dust looking for buyers, just check ebay listings for OE parts of various types.  I would not buy from the box stores if you can get the same ones elsewhere.  On my knock sensor, no performance issue, was throwing the code.  How common is it for the codes thrown to be inaccurate?

[1 Lucky Texan]

I have had 'spurious' codes thrown 3 times on my 2 soobs, (even put my WRX into 'limp' mode) bad batteries everytime but, I suppose other issues like charging system or poor grounds or 'dirty' connections, etc. could cause the same type of problem.

And often codes are thrown due to issues unrelated to the 'official' definiton/description of the code's involved. That is, just because a rear O2 sensor has 'catalytic converter efficiency' in it's description, doesn't necessarily mean the catalytic converter is bad.

[nipper]

1 hour ago, 1 Lucky Texan said:

I have had 'spurious' codes thrown 3 times on my 2 soobs, (even put my WRX into 'limp' mode) bad batteries everytime but, I suppose other issues like charging system or poor grounds or 'dirty' connections, etc. could cause the same type of problem.

And often codes are thrown due to issues unrelated to the 'official' definiton/description of the code's involved. That is, just because a rear O2 sensor has 'catalytic converter efficiency' in it's description, doesn't necessarily mean the catalytic converter is bad.

Yes the trick is to look for a common denominator when you have multiple unrelated codes.

 

I often wonder how many cats have been sold wrongfully.

Something else to look for, on csrs with start/stop they have a second battery that can throw all sorts of unrelated error codes when its bad. Same for EVs.

[ThosL]

Ok, timing seemed off today so knock sensor is apparently not working right.

Someone said I need to go to the dealer to have them reset it, I have not heard this before.  1997 2.5.  

[1 Lucky Texan]

If the system is working correctly, it is 'self adjusting' . This is a very common failure on 15+ year old cars. Many people have fixed this. Of course, it's possible to have more than one problem, it's possible to get a bad new part, but, it is not anything special, expensive or requiring a visit to a dealer.

[ThosL]

That's what I thought as when replacing one on a 2.2, code went away.

I ordered another one will see if it makes any difference.  I was thinking I might have damaged the core wiring when I pulled the unit out initially.  A mechanic's quick change has turned into a major headache.

I changed out the coil yesterday, a ten minute job.

The old unit had corrosion dust in the wire plug holes!

[1 Lucky Texan]

you may need to pull the battery cable for a few minutes or clear the code with a scanner. Or, you may not see the code clear for 5-6-7 drive cycles.

[ThosL]

Performance still indicates bad knock sensor, ordered another one.  I reached in there a few days ago to make sure the connector was solid which seemed to address it but the problem of power lag came back.  I ordered an apparently oe unit.