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Thread: Loads of detonation when its hot. Can't seem to get rid of it

  1. #1
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    Loads of detonation when its hot. Can't seem to get rid of it

    Scan9495 log is here and I am attaching the current BIN.

    I have been chasing this detonation issue since this engine was assembled. This log shows that at times, its pulling 5 degrees of timing out to get rid of it, but its still there. 383, TrickFlow injectors, TrickFlow 195 heads, Cam is 224/230 .560/.544 112 LSA . 160 T-stat. Car is running 91 - which is the best I can get around here. The issue is really bad when its 90 degrees or above, and/or after the car is sitting in traffic. The trans also shifts a bit funny. Sometimes after taking off and going WOT, it'll upshift to the next gear at a low RPM

    Everything is new. New opti, wires, plugs, MAF, MAP, ECT, coil, ICM - you name it, its new.

    If anyone can take a look, I'd sincerely appreciate it. At this point, I am considering a different cam because nothing else seems to be working with this detonation. I literally have no ideas left.

    Edit: Fuel pressure is good at the rail.
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    Last edited by atlantadan; 05-19-2017 at 02:54 PM.

  2. #2

  3. #3
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    Good question, Steveo. But I know its real - I can hear it
    Last edited by atlantadan; 05-20-2017 at 04:12 AM.

  4. #4
    Fuel Injected! steveo's Avatar
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    ok, so you hear an actual noise and so does your knock sensor, and it thinks its knock and it pulls timing, and the noise still happens?

    sounds like mechanical noise to me. valvetrain noise, exhaust leaks, loose spark plugs, can all sound like knock.

    the fact it's temperature dependent also might be a clue.

    do you have any other evidence you're experiencing detonation? have you looked at your plugs?

    you can use eehack to pull up to 15 degrees of timing manually while driving to see if you can get rid of the 'noise'. if it's the kind of knock that you assume, you should also be able to add timing and make the knock worse, or remove timing and make it go away, controlling the noise like a volume knob. if that doesn't do it, it's not knock.

    i looked at your bin too and your timing advance is ridiculously low, unless this is a 5000lb+ flat windshield type vehicle. there's no way. (barring something crazy like a glowing peice of slag in your combustion chamber serious carbon buildup, or a serious lean knock)

  5. #5
    Fuel Injected! steveo's Avatar
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    i just ran your log through trimalyzer's knock mapper...

    do you feel that log is a fair representation of the symptoms you're experiencing? (did you actually take it during a knock event?)

    the events seem localized to ~2000rpm and ~60 map. your timing advance in that cell is 'bout 35 degrees. stock f-body timing table is 38. this leads me to believe you haven't really tried to correct for the knock in the region it's happening..

    if it is truly spark knock, and that log is a good one, why don't you dump some timing in that region?

    if you determine that it's false knock, you could simply disable knock detection in that 60-70 kpa range after removing a few extra degrees of timing to be safe.

    see attached.
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  6. #6
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    Quote Originally Posted by steveo View Post
    i just ran your log through trimalyzer's knock mapper...

    do you feel that log is a fair representation of the symptoms you're experiencing? (did you actually take it during a knock event?)

    the events seem localized to ~2000rpm and ~60 map. your timing advance in that cell is 'bout 35 degrees. stock f-body timing table is 38. this leads me to believe you haven't really tried to correct for the knock in the region it's happening..

    if it is truly spark knock, and that log is a good one, why don't you dump some timing in that region?

    if you determine that it's false knock, you could simply disable knock detection in that 60-70 kpa range after removing a few extra degrees of timing to be safe.

    see attached.
    Thanks Steveo. I am 100% certain that log is a good one and it was taken during a knock event. It always happens in the same range of throttle/load/RPM, so that map looks accurate too. I am certain it isn't false knock - its loud and sounds like it had a tank of bad fuel.

  7. #7
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    Quote Originally Posted by steveo View Post
    i looked at your bin too and your timing advance is ridiculously low, unless this is a 5000lb+ flat windshield type vehicle. there's no way. (barring something crazy like a glowing peice of slag in your combustion chamber serious carbon buildup, or a serious lean knock)
    Its a Caprice wagon with 3.08's, so that gear isn't helping things. Plugs didn't show any real obvious signs of detonation, but I'll pull them again to check. The car is 11.6:1 CR with a .039 quench. It didn't really start making a lot of racket until the temps got over 90 here. The IAT is usually 120+ when its knocking.

  8. #8
    Fuel Injected! spfautsch's Avatar
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    Not to diminish your report that you are hearing audible knock, but you might want to clarify what you mean by "loads". Are you hearing a lot more than the knock plot is showing? Because I would stab a man in the heart with a butter knife to have a knock plot that looked that clean.

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