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Typical causes of false knock?

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GottaBuick

Member
Joined
Dec 10, 2007
Messages
79
Good morning everyone, I have a pretty stock 87 GN with the modifications in my signature, which exception to the 340 Walboro and FPR which I haven't had time to install yet. I don't drag race at all or run the car hard very often, but do have some spirited runs through the gears and an occasional full throttle kick down onto the on-ramp. I never see any knock on the scanmaster during these runs with millivolts reading around 810 and my wideband showing 11-11.5 everytime, but when I hit recall after the run I usually see 2-4 degrees of knock at 810-815 and mid thirty MPH. Am I correct in assuming this is false knock at shifts or something hitting since it doesn't even stay on long enough to show on the screen during the run only at recall? the car runs great, only has 39K miles, running stock chip too.

If you don't think it is knock at shifts, where are typical places to find false knock causes.

Thanks,
 
Take a look at the downpipe and make sure it isnt contacting the frame rail. Make sure your motor mounts are in good order.
 
If your over 14psi on the stock chip and running less than about 95-96 octane the knock is not false.
 
I have the same issue. A little blip at 38 MPH , especially when I nail it when already moving. I thought my issues were worn motor mounts, I could see a small ding in my downpipe where it was hitting the A arm. I replaced the DS motor mount and the KR lessened. I still need to do my transmount.
 
If your over 14psi on the stock chip and running less than about 95-96 octane the knock is not false.

No, it is still stock wastegate and boost (93 oct), the highest I have ever seen the boost go is like 13 psi on a cold night (on autometer mech gauge), usually is around 11-12 psi.
 
I have the same issue. A little blip at 38 MPH , especially when I nail it when already moving. I thought my issues were worn motor mounts, I could see a small ding in my downpipe where it was hitting the A arm. I replaced the DS motor mount and the KR lessened. I still need to do my transmount.

Intresting, that does sound like mine, usually after kickdown and already moving (but not more than 30 mph). I still plan on looking at the mounts tonight.
 
Maybe you could try surrounding and wrapping the knock sensor with plumber's putty to help eliminate some external clunks and sounds that could trigger false knock detections.
 
Maybe you could try surrounding and wrapping the knock sensor with plumber's putty to help eliminate some external clunks and sounds that could trigger false knock detections.
so you have done this?
 
I have not had any issues with false knock but recall back many years ago at the GS Nationals when they used to have a turbo tech session with people like Lawrence Conley, Ken Duttweiler, etc.. on a panel answering questions and that tip was brought up then. It makes sense and is simple to give a try. In fact, at that tech session, it was said to screw the knock sensor in hand tight... so it was a little looser than normal and then wrap it with plumbers putty to help screen out noises that were not actual detonation.
 
plumbers puddy, well the logic sounds solid. that could be worth a shot, if anyone has done this with significant results please post.

Thanks again everyone.
 
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