legacycentral bbs

Heya folks,

I have a 1990 Legacy sedan, awd, auto. When the car is cold, I often get the "Check Engine" light, and only on the first run of the day. This goes away after the car is properly warmed up (anywhere from 3 to 20 min). I pulled the codes today, and I got "22", which is supposed to be the knock sensor. Do these symptoms sound correct for the reading I got, and if so, how expensive and difficult are these to replace?

Any help/info is greatly appreciated.

Thanks

Rish

You're new here, so I'll give you a break and do this first search for you

http://bbs.legacycentral.org/viewtopic.php?t=50

If your car has the original knock sensor, you may want to consider replacing it with the updated part.

The original sensor had a problem where small cracks would develop in its ceramic casing, so excessive non-knock-related vibration would get interpreted as sound.

When your engine is cold it's louder and vibrates more, so it would make sense that that's when knock sensor problems would be most noticeable.

It's also possible that your connector is just loose, and when the engine vibrates it comes loose.

The updated knock sensor is Subaru part number 22060AA031 and lists for around $50. It's a little annoying to replace if you have fat arms like me, but it's doable in about half an hour or so, without removing any other parts. It's mounted on the rear driver side of the block just under the intake runner.

You can tell if yours is the old or new part by looking at the color of the connector on the sensor (you may have to unplug and clean it first): the old one has a gray connector and the new one has a white connector.

Thanks for the break.

Rish

vrg3 wrote:When your engine is cold it's louder and vibrates more, so it would make sense that that's when knock sensor problems would be most noticeable.

But vrg3, when the engine is cold, isn't it in open-loop? My Legacy is downright fast when the engine is cold, and then starts hesitating when it gets warm ....

Yes, it's open loop when cold... But it does vibrate more because the oil isn't as slick, the fuel's not atomizing as well, parts don't mate up quite as well, and so forth.

You say your car's fast when it's cold -- I hope you're not pushing it hard before it warms up! But I think the ECU does keep timing fairly advanced when the engine is cold, which may make the performance better.

Mine's much faster when cold, too, which makes it frustrating because I won't push her over 3500 until warm.

Steve

If I were you, I would just replace the knock sensor with the new one if you're getting the code for a faulty knock sensor.

My car is faster when cold, but i don't drive hard at all until the temp is up to normal. Even when the temp guage reads 1/4 if i go over 3,000-3,500 rpm i can see the guage quickly go from 1/4 all the way to the "C" line in a matter of seconds. My theory is that the thermostat or thermostat gasket isn't sealing correctly, allowing water to get pushed past at higher rpm's when the thermo is fully closed.

I figure that this probably isn't too good for the engine and could probably lead to some warpage due to the differing temperatures, so I let her warm up all the way before I "drive" her.

I should probably get a T-stat from the stealership along with a new gasket and see what that does...But i'm a broke @$$ college student looking for a job right now, so I lack the funds for that.

I don't push my car hard cold or hot , but when merging into traffic or whatever when it's cold, I definitely notice more power when the engine is cold...

I know better than to beat it when it's cold, it is aluminum after all

I go really easy on it when it's cold... But once it's warmed up, I push it hard.

But, yeah, I guess it makes sense that when it's cold it would make more power, due to the advanced timing and also the fact that the intake manifold and throttle body aren't heating the air up to 200 degrees. Maybe the slightly richer mixture helps too... I do know that one of the things the Torque Chip/ProECM does is make the ECU think the coolant temperature is slightly lower than it is, at least when warmed up.

I can solve this one for you coz its the same as I was getting a wekk or so back, take the knock sensor off and clean up the face that mates to the engine block as its probably crudded up and cant make an earth with the engine until the engines warmed up (sounds implausable but it really did cure mine straight away with no recurrance).

DOA wrote:I can solve this one for you coz its the same as I was getting a wekk or so back, take the knock sensor off and clean up the face that mates to the engine block as its probably crudded up and cant make an earth with the engine until the engines warmed up (sounds implausable but it really did cure mine straight away with no recurrance).

very interesting.....even though my sensor is relatively new....I may give that a shot as well.

So I went to Subaru and ordered the knock sensor and it's been in my glovebox since Thursday. I finally got time to install it, so I pulled out my Haynes manual, which did a great job in confusing me. According to the manual, I have to drain the coolant before I remove the old sensor. Now i haven't been able to find this mentioned elsewhere on the site, so if someone could please clarify, I would be extremely grateful. Also, the book and one other member has mentioned threads that come pre-greased so don't wipe it etc. etc. when installing the sensor. Now all I got from Subaru was the unit itself (which has no threads on it) in a small box. Am I missing any other hardware here?

Once again, thanks for any information and assistance provided.

Rish

Toss your Haynes manual aside for this procedure. I don't know who wrote it up, but most of the steps in there are entirely unnecessary. The main thing is the removal of the intake manifold. That's hogwash. All of us that have replaced ours have not so much as touched the manifold.

There is no coolant that even comes close to the sensor, you won't see a drop of it.

And the sensor is all you need, just unbolt the old one and unplug it, and take that bolt and put the new one on. Definitely have a magnetic reacher handy when you do this, as you will almost asuredly drop the bolt somewhere...

Ok, the new sensor is in! Looks like it was really needed, because the old one still had the grey connector, and was also badly cracked (guessing it was the orignal). Getting it in went pretty smoothly, aside from a few scraped knuckles, and no thanks to subyluvr's advise on keeping a magnetic pick-up tool handy. Now I just have to see if it makes much of a difference over the coming week.

Thanks to all for the information and advise given on this post.

Cheers,

Rish