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Thread: Knock retard 'feel'

  1. #1
    Lifetime Member Cougar281's Avatar
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    Default Knock retard 'feel'

    For the experts out there... How much knock retard under power does it take to 'feel something'? I just bought a 2019 CT6 3.0TT that I strongly suspect was filled with 87, while it requires 93. I haven't worked through that tank yet (getting there), and of course when I get it down to fumes, I'm going to fill it with 93 like it's supposed to get and I suspect the issue will go away, but I've noticed a 'shuddering' under load, and when I set up some PIDs to log with my V2 and did so, and marked the logging when I felt it, when I reviewed the logs, there was knock retard where I marked the log when I felt 'something'. It was only about 3*, which doesn't seem like much, but it was there. Is 3* of KR actually enough to 'feel something'?


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    Last edited by Cougar281; June 21st, 2022 at 02:54 PM.

  2. #2
    Joe (Moderator) joecar's Avatar
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    Don't drive it like that, but rather mix in some 100 or 120 to bring the octane up.

  3. #3
    Lifetime Member Cougar281's Avatar
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    Quote Originally Posted by joecar View Post
    Don't drive it like that, but rather mix in some 100 or 120 to bring the octane up.
    Welp, that tank was run down to near fumes while being gentle (No idea where I'd even get 100 or 120 around here, and most out there said as long as you stayed out of the boost, it would be fine, so that's what I did - it is a low static compression motor, unlike the 3.6 that was in the CTS I had before this that was 10.5:1 or 11.5:1 and called for 87, so boost is really where the need for 93 comes in), and then loaded it up with a full tank of 93. After that and a decent amount of time to ensure that the 93 (or probably 92.6 or something based on the the amount of fuel added vs amount in the tank), it's still pulling the same amount of timing. I did some more logging, using the T87A for the transmission since EFILive doesn't support the T93 in any way, not even just scanning, and based on what it showed, I suspect the problem is in the transmission. In the attached log, looking at the 'TCSLIP' PID, which according to the description, is 'Transmission Clutch Slip', not 'Torque Converter Slip', the spikes of slip EFILive logged is exactly what it feels like. Further, I logged using GDS2, which doesn't seem to have any PIDs related to slip other than the Torque Converter, which when logged and I was getting the 'shuddering', the GDS2 graph showed zero Torque Converter slip, so I have a suspicion that the problem is in the transmission :(. I'll have to get it to the dealer and see what they have to say.
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