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Knock sensor: do they go bad?

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by bsd43, Sep 27, 2011.

  1. bsd43

    bsd43 Member

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    I have an 06 with 105000 miles. Since about 95000, I've been starting to get what sounds like a fuel knock with medium-high load on the engine. Thought it was carbon at first, but a few applications of Techron didn't clear it. Higher octane does seem to solve it.

    Do the knock sensors go bad on a Prius? What's the proper way to diagnose the knock sensor on a Prius? (can't exactly bang on the block with a wrench at idle and listen for fuel adjustments on a car that doesn't idle, heh).
     
    #1 bsd43, Sep 27, 2011
  2. seilerts

    seilerts Battery Curmudgeon

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    Are you the original owner? Would you say that the oil has been changed every 5000 miles and was never run low?

    Over time, carbon builds up on top of the piston. This causes hot spots and increases compression. If you increase compression, you need to increase octane, or you get knock. Sounds like you know all this, though. 105000 seems a little young to be having this much of an effect as well.

    But, I think beating on the block is still the first thing to try. You can make the car idle by following Hobbit's procedure.

    Prius base idle
     
    #2 seilerts, Sep 27, 2011
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  3. bsd43

    bsd43 Member

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    Original owner, always Mobil 1 synthetic, never lost oil.

    Even if there's carboning, I thought that the knock sensor would immediately retard timing when it's detected.

    Thanks for the link on how to get an idling engine! But, is there even a set of timing marks to shine a timing light on? Or is that part of the diagnostic gizmo that a shop has?

    I confirmed today with another load of 91 octane that it goes away, so it's gotta be knock. Maybe it's just cheapest to buy higher octane fuel from now on...
     
    #3 bsd43, Sep 28, 2011
  4. seilerts

    seilerts Battery Curmudgeon

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    If you have a scangauge or scanner with live data, you can watch IGN and see if it retards when you have someone beat on the block.

    The only other thing I can think of is an issue with the oil control valve, which adjusts camshaft timing. Hard to believe that you are having any kind of a problem running Mobil 1.
     
    #4 seilerts, Sep 28, 2011
  5. edthefox5

    edthefox5 Senior Member

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    You are correct unless the timing is so far out its out of retard parameter. Carbon fouling is rare on a modern car at 105K miles especially on a Prius which has a pretty strict mixture program.

    I would pull the plugs first to see whats going on in the cylinders. Check the ignitor connectors too especially where they attach to the plug itself for corrosion.
    The plug condition will tell if there's a carbon fouling for sure.

    Then I would check the tiny oil filter for the Variable Valve timing system. The VVT advance is oil driven. The filter may be clogged or the VVT may be stuck in advance all the time. Its spark advance for sure if 91 octane fixes it.
    Please search back my old posts as I have a very good description on how to remove the filter. Its pretty easy to check.

    And a hot motor will ping before a cold motor. Without a Scangauge its impossible to know the engine operating temp but I would investigate that also. How's the ICE coolant condition?
    Your way overdue for new coolant and a new thermostat if there the oem stuff.
    And way overdue for Inverter coolant.
     
    #5 edthefox5, Sep 28, 2011
  6. bsd43

    bsd43 Member

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    I changed the plugs at about 100k, and the old plugs looked fine. Too bad I didn't keep them, else I'd take some pictures.

    Hm, I figure that if the engine timing advance doesn't do its job, the variance would be noted by the computer, and the CEL would come on. On my other car (BMW), where the valve timing was also oil pressure controlled, I had to change out a leaking VANOS seal so that the timing would advance properly.

    Come to think of it, it only happens in hot weather (well, Bay Area "hot"). Engine coolant is about 40k old, inverter coolant about 20k. Original thermostat.

    Maybe it's time for me to buy a ScanGauge2 so that I can see temperatures and ignition timing, among other things... New toy!
     
    #6 bsd43, Sep 28, 2011
  7. ccdisce

    ccdisce Active Member

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    #7 ccdisce, Sep 28, 2011
  8. seilerts

    seilerts Battery Curmudgeon

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    Even though there is a DTC for a clogged oil control valve filter (Ed's post), it is not clear just how clogged it has to be for a code to be thrown. Over in RAV world, a guy short blocked his main bearing knocking 1AZ for a reman 2AZ (2.0L -> 2.4L) and couldn't figure out the weird clacking sounds at idle. Turned out that the OCV was clogged with the same sludge that has plugged the oil pickup screen on the 1AZ. No code.
     
    #8 seilerts, Sep 28, 2011
  9. bsd43

    bsd43 Member

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    #9 bsd43, Sep 28, 2011
  10. bsd43

    bsd43 Member

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    Update: ran 2 tanks with Gumout Regane (which has a high dose of PEA cleaner). Now things are normal even with 87 octane. So I'm going to chalk this up to carboning and gunk in the combustion chamber, and the knock sensors were just not activated with the light knocking I was experiencing.

    I also just got my OBD-II to USB cable for PriiDash via eBay. Let the geeking begin...
     
    #10 bsd43, Oct 16, 2011
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  11. davisnc

    davisnc Junior Member

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    I am trying to diagnose my spark knock. What is the process of "beating on the engine block" at idle? I have searched but haven't been fortunate enough to find any details.
     
    #11 davisnc, Jul 20, 2015
  12. bisco

    bisco cookie crumbler

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    how many miles on her?
     
    #12 bisco, Jul 20, 2015
  13. davisnc

    davisnc Junior Member

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    Long time since I posted, but I have 175k miles now. Spark knock is much worse in summer / with warm engine.
     
    #13 davisnc, Jun 23, 2016
  14. bisco

    bisco cookie crumbler

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    sorry, no idea. maybe someone knowledgable will chime in, all the best!(y)
     
    #14 bisco, Jun 23, 2016
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