legacycentral bbs

Got a flash light and looked under the intake manifold and i can see the knock sensor is cracked. Is it possible to make the car idle a little hard, and give me only 300km max fuel mileage before i need to fill up, and make the exhaust(stock) loud? I am going to pickup a new one, but its coming in the mail. Just want to know though, thanks.

ericem wrote: Is it possible to make the car idle a little hard, and give me only 300km max fuel mileage before i need to fill up,

Yup.

I drove for a week with my knock sensor loose (the bolt apparently worked its way out so the sensor could move a good 1cm). Anyways, the idle was rough and I got ~19-21 mpg for pure highway driving. One I tightened the bolt down, all was better

exhaust being loud though is probably another issue.
loose manifold/bad mani gaskets or a rust through somewhere maybe

I hope this is also what my problem is. The idle isnt really rough, but my gas mileage is about the same and I have fairly foul smelling exhaust which makes me think its something else too.

kills wrote:I hope this is also what my problem is. The idle isnt really rough, but my gas mileage is about the same and I have fairly foul smelling exhaust which makes me think its something else too.

well, there are definitly no exhaust leaks, the sound comes right out the muffler.

Just wondering what this sensor controls, becauase if it makes the engine run rich, then im thinking it could create some extra noise.

ericem wrote:Just wondering what this sensor controls, becauase if it makes the engine run rich, then im thinking it could create some extra noise.

IIRC, it controls the timing advancing. Rich/leanness is controlled by the O2 sensor...

BSOD2600 wrote:

ericem wrote:Just wondering what this sensor controls, becauase if it makes the engine run rich, then im thinking it could create some extra noise.

IIRC, it controls the timing advancing. Rich/leanness is controlled by the O2 sensor...

oh i thought they both do the same thing So what exactly are timing advances?

you have to be carefully not to overtighten those knock sensors as they are a plastic surrond and they will crack if torqued too high

ericem wrote: So what exactly are timing advances?

on these cars you dont need to know
(unfortunately)

A bad knock sensor will play hell with the car.....replace it.

gt2.5turbo wrote:you have to be carefully not to overtighten those knock sensors as they are a plastic surrond and they will crack if torqued too high

thats what i was just about to ask now Is there a specific torque? Should i use blue locktite?

Well as off right now the car runs prertty dam good But more vibration is noticed from the engine as it revs up. Knock sensor on the way. Can this damage the engine?

no do not use lock tite, your just asking for trouble. subaru's knock sensors are known for being bad. http://legacycentral.org/library/literature/knock.htm

you said your waiting for one in the mail. after that you should be good. as to whether the knock is bad. its kind of depends on your ear. most likely not bad, if your oil light comes on i would be worried. but i think your good. any thoughts guys?

I probably drove around on a broken knock sensor for years and never heard any engine knock.

Manarius wrote:I probably drove around on a broken knock sensor for years and never heard any engine knock.

That's not the point, the point is that the cracked sensors will retard timing, which decreases any chance of knock, but also decreases power.

I've pullled about a dozen old knock sensors off these motors, and they were all cracked in the same place. The plastic on each side. I don't think it affects a whole lot. I was getting 29.5mpg with it like that for years. Now if the metal cracks, thats a way different story.

I didn't see it mentioned above...

I think there is an upgraded Knock Sensor. They made the plastic a different color (went from black to grey or vice-versa). These supposedly don't crack as easy. I haven't pulled an EJ with a stock Knock Sensor that wasn't cracked yet.

could this be why so many of us have bad fuel eco...?

I think as a group we should really find out why some of us get REALLY bad fuel eco and some get... i would say ok fuel eco (i cant see a Subie ever getting good fuel eco)

My initial guess would be no. I don't think the Knock sensor does anything to fuel until it senses a out of bound condition. If the knock sensor was constantly altering fuel then your ECU should eventually go into limp mode.

I get relatively consistant fuel mileage with all three of my cars. Two AWD and one FWD (this is my second FWD). The FWD get around 30-34 mpg (have gotten 36 on extremly long trips) and the AWD det anywhere from 23-27 MPG.

My car seems to know when the seasons change cause every spring when the weather really starts to worm up it will do what i can only describe as blipping the throttle which gives the whole car a small but sudden jerk. Could this be related to the knock sensor? It ran all winter with no problem and did the same thing last year.

I'm not 100% sure that a cracked knock sensor would be the problem. It definitley could be I suppose. I guess if it were me and my knock sensor was cracked I would replace it with the new upgraded one (if you search I think you'll find the new PN around here somewhere, I think I've seen it listed on here).

As far as fuel mileage goes, you should see a definite fuel mileage change from season to season (especially where you have a wide variety of temperatures and humidities, like here in NY). A lot of things play into it. I would think air and fuel temperature would effect the flame characteristic which is providing power. When this is degraded, so is your fuel mileage and power. I see a noticeable change when the temperature increases to around 70 degrees with very low humidity.

As far as your bucking problem goes. The new knock sensor was like $20-$30 IIRC...might as well replace it (note that you DO NOT have to remove the manifold to do this job as some manuals say - and you don't lose coolant as the Haynes manual says).

The knock sensor on my Legacy was cracked, and it would throw false knock codes all day long (espically in the rain, or if I hit a bump too hard).

Forester had the same thing happen.

I got an updated sensor from a junkyard for $10 for the Legacy and never had a problem. I had a JDM knock sensor lying around for the Forester, and that too, fixed my problems.

BAC5.2 wrote:The knock sensor on my Legacy was cracked, and it would throw false knock codes all day long (espically in the rain, or if I hit a bump too hard).

ej22t kid:
Thats kind of what I was wondering. Seems if your car started to buck from a bad knock sensor you would get a knock code (check engine light would come on). Have you ever tried pulling the codes from the ECU to see if its storing anything? Even if it isn't...like I said before, I would just replace the cracked knock sensor for the amount of money it costs.

this weekend i am putting in the td05 16g and new starter so i will check the knock sensor and see if its cracked. i pulled some codes a while back but never got the knock code

just changed the knock sensor and WOW what a difference, RPM's seem more consistant and NOOO hesitation AT ALL, runs sooooo smooth now, and feel way quicker.

now i got my new speedocable in the car shifts so nicely this is awsome!

by the way my old knock sensor looked to be cracked because it rusted, not because of to much pressure being tightened. But either way i made mine snug.