The Subaru SVX World Network   SVX Network Forums
Live Chat!
SVX or Subaru Links
Old Lockers
Photo Post
How-To Documents
Message Archive
SVX Shop Search
IRC users:

Go Back   The Subaru SVX World Network > SVX Main Forums > Technical Q & A

Reply
 
Thread Tools Display Modes
  #1  
Old 03-20-2005, 12:16 PM
NJSVX
Guest
 
Posts: n/a
Knocking Sensor

Can anyone tell me what the knocking sensor is? When I check the code on my SVX, it says its the knocking sensor. What is it linked to, what needs to be changed, and its location.

Thanks,
Adam
Reply With Quote
  #2  
Old 03-20-2005, 01:27 PM
Beav's Avatar
Beav Beav is offline
Not as old as Randy
 
Join Date: Nov 2001
Location: Louisville, KY
Posts: 3,883
Significant Technical Input
Knock sensors detect detonation, aka 'knock'. High compression, coupled with incorrect ignition timing, too low octane fuel, high combustion temperatures, carbon build-up in the combustion chamber or on the piston and an inoperative EGR system can all cause it to occur.

Knock sensors 'listen' for specific frequencies that indicate the problem. They are piezo devices that convert motion into voltage. As such, they always generate some voltage when the engine is running. What the ECU is looking for is a particular range of frequency and voltage. Once a specific threshold has been crossed the ECU will react by retarding timing in stages and watch for continuing detonation. Over a specified amount of time, if the threshold is no longer crossed the ECU will begin returning the timing to its original program.

A knock sensor code does NOT indicate that the engine is knocking. The ECU expects to see some output from the sensor(s) whenever the engine is running, as the engine will always generate some 'noise'. This 'noise' doesn't necessarily have to be in the detonation region. It is the lack of any signal that will cause the ECU to store a code.

With all that being said... The sensor used on the SVX is very similar to those found on many Nissans. They are notorious for throwing codes, both on the SVX and on Nissans. I've replaced a number of them only to later find that they continue to throw codes. I have watched their signals while back-pinning at the ECU and have watched them set codes while there was absolutely no signal deterioration. I've spoken to many other techs about this and we've all come to the same conclusion: it's a glitch in either the ECU's internals or the ECU's programming.

Additional info: a knock sensor code will never turn on the 'check engine' light. It will remain in memory until the memory is cleared.

What should you do? Hmmm... well the proper thing to do is to monitor the sensors with a graphing meter or o-scope for drop-outs. Orrrr... clear the code, start the engine and let it run for a few minutes and re-check the codes. Chances are if it immediately resets the code you have one or two dead sensors, if not the code was probably a glitch. Best bet? If you can, unplug and re-plug the sensors a few times to clean their connector contacts.

BTW, if you decide to replace a sensor Subaru issued a TSB years ago stating that the sensors should be replaced in pairs. If you need help replacing them use the search button and I am positive you'll find all kinds of help previously written.
__________________
ASE Certified Master Automotive Technician w/L1.
ASE Certified Master Medium/Heavy Truck Technician.
Certified EVT (Emergency Vehicle Technician)
Reply With Quote
  #3  
Old 03-20-2005, 08:27 PM
SVXRide's Avatar
SVXRide SVXRide is offline
Official AutoX Part Breaker
Subaru Gold Contributor
 
Join Date: Aug 2002
Location: Midlothian, VA 23112
Posts: 8,138
Registered SVX
Normally, I'd say "check my locker for pics" as I just finished replacing both knock sensors last month ...added notes in each picture and everything....maybe you can petition Chris to bring the lockers back a little sooner
-Bill
__________________
Retired NASA Rocket Scientist

Most famous NASA "Child" - OSIRIS-REx delivered samples from asteroid BENNU to Earth in Sept. 2023

Center Network Member #989

'92 Fully caged, 5 speed, waiting for its fully built EG33
'92 "Test Mule", 4:44 Auto, JDM 4:44 Rear Diff with Mech LSD, Tuned headers, Full one-off suspension
'92(?) Laguna, 6 spd and other stuff (still at OT's place)
My Locker
Reply With Quote
  #4  
Old 04-12-2005, 10:02 PM
Bxsvx Bxsvx is offline
How fast is fast?
 
Join Date: May 2003
Location: Bronx, NY
Posts: 417
Send a message via AIM to Bxsvx
What made you change the sensors, except for seeing the cracks? any sounds or anything from the engine?
Reply With Quote
  #5  
Old 04-13-2005, 12:47 PM
Earthworm's Avatar
Earthworm Earthworm is offline
Meow!
 
Join Date: Mar 2002
Location: Winnipeg, Manitoba
Posts: 11,957
Send a message via ICQ to Earthworm Send a message via AIM to Earthworm Send a message via MSN to Earthworm Send a message via Yahoo to Earthworm Send a message via Skype™ to Earthworm
He got a code.
Reply With Quote
  #6  
Old 04-13-2005, 02:14 PM
SVXRide's Avatar
SVXRide SVXRide is offline
Official AutoX Part Breaker
Subaru Gold Contributor
 
Join Date: Aug 2002
Location: Midlothian, VA 23112
Posts: 8,138
Registered SVX
Quote:
Originally Posted by Bxsvx
What made you change the sensors, except for seeing the cracks? any sounds or anything from the engine?
Dyno runs were down on power at wheels -- knock sensors close loop on ignition advance allowed -- the cracked housings and brittle wiring could both contribute to potential incorrect sensor input to the ECU
-Bill
__________________
Retired NASA Rocket Scientist

Most famous NASA "Child" - OSIRIS-REx delivered samples from asteroid BENNU to Earth in Sept. 2023

Center Network Member #989

'92 Fully caged, 5 speed, waiting for its fully built EG33
'92 "Test Mule", 4:44 Auto, JDM 4:44 Rear Diff with Mech LSD, Tuned headers, Full one-off suspension
'92(?) Laguna, 6 spd and other stuff (still at OT's place)
My Locker
Reply With Quote
Reply

Thread Tools
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off

Forum Jump


All times are GMT -6. The time now is 10:54 AM.


Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2024, vBulletin Solutions, Inc.
© 2001-2015 SVX World Network
(208)-906-1122