Sources of knock (false?) - GM Forum - Buick, Cadillac, Chev, Olds, GMC & Pontiac chat


1992-1999 Series I L27 (1992-1994 SE,SLE, SSE) & Series II L36 (1995-1999 SE, SSE, SLE) and common problems for the Series I and II L67 (all supercharged models 92-99) Including Olds 88's, Olds LSS's and Buick Lesabres Please use General Chat for non-mechanical issues, and Performance and Brainstorming for improvements.

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Old 09-12-2005, 08:04 PM   #1
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While I still had some toluene on my gas from Friday, i got some scanning done. The toluene should have given me ~95.5 octane. Scans just now around town and on the highway revealed similar amounts of knock retard as with 93 octane, at most, I saw 5 degrees of retard. However, going 70 mph on the highway, floor it so it shifts to second, I saw 17 DEGREES for a moment, dropped to 11 then dropped off.

Now I think I have some false knock. What are the sources of false knock retard on a Series I L67?
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Old 09-12-2005, 08:05 PM   #2
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wow.

perhaps your knock sensors are bad?
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Old 09-12-2005, 08:08 PM   #3
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I replaced the knock sensor last summer (there is only 1 on a 92 L67)
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Old 09-12-2005, 08:10 PM   #4
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i have also read that metal on metal may set them off.

also, perhaps it is knocking. you seafoam lately?
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Old 09-12-2005, 08:21 PM   #5
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I'm hoping some people know of some common places to check.

Keep ideas coming...
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Old 09-12-2005, 10:32 PM   #6
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I know you said false but,
Oil. I'm convinced that my heads were leaking oil causing predetonation.
Does you car loose a noticeable amount of oil between oil changes?
Other stuff:
exhaust leak or tick
Anything loose in the engine bay
Have you checked your plugs?
One cylinder might not be firing as well as the others, sending unburnt fuel past your O2, and could cause your engine to run lean.
Or maybe a clogged injector?
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Old 09-12-2005, 10:36 PM   #7
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Looses lots of oil, only visible leak is the LIM
Exhaust leak maybe
Plugs are a year old, haven't looked at them recently
I'd notice if a cylinder wasn't firing
Injectors were cleaned/rebuilt last year
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Old 09-12-2005, 11:06 PM   #8
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Exhaust leaks are a big suspect on the S1 due to cracks. Or the knock sensor itself rattling. Did you use any kind of goop to put it in? What makes you so sure it'* false? Octane alone cannot kill all KR. If you have an exhaust restriction, no amount of octane will save you.
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Old 09-12-2005, 11:14 PM   #9
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I figured it was false cause it didn't change with higher octane. I guess I could be wrong. What could cause the massive KR at the top of second? I installed the knock sensor dry, except for the red threadlock that was already on it.

I'm starting to get the feeling it will completly disapear when I swap the heads, LIM, and manifolds.
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Old 09-12-2005, 11:16 PM   #10
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Yeah there'* really quite a few things that could cause it. Make sure your trans tube isn't rattling, tighten down your exhaust, wiggle the idlers to make sure one isn't going crazy at high rpm'*, and make sure you didn't overtighten the knock sensor when you installed it. That'll make it overly sensitive.
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