I do not know what knock or false knock feels like, however, when my car is at idle, sometime the rpms will dip about 100 or so and the lights will dim a bit, (almost sounds electrical). In addition, when cruising around when I accelerate the car is real bumpy until 2500 rpms or so, but it is pretty much unnoticable after that.

Could this be false knock?


I have shorty headers, and a catback exhaust... ive heard and seen through searches that has been the cause of many knock issues through the lt1 module.

Anyone have any take on this?

 

You need to scan your engine while driving (Diacom, Scanmaster) to see if your knock sensor is detecting knock and pulling timing. Headers can cause false not; you can use race gas (100 octane) to see if the knock goes away. If it goes away then it's true knock; if it doesn't go away, then it's false knock and you can desensitize the knock sensor or try a LT4 knock sesnor.

 

yeah, I am aware of the lt4 KM...

This only happens when it is Warmed up as well...
and only when I push the gas down a certain amount, if I lightly press it and kind of ease into it, the shakyness can usually be avoided... but if I get on it.. or put it half way it feels real bad.

 

Sorry to jump in and sound like a laymen, but can somebody explain the difference between true knock and false knock?

I think I have it right I'm just not quite sure.

And if it is true knock, would running a higher octane be safer until the problem was fixed?

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And back to the original poster, do you have any exhaust leaks? I was experiencing something similar to that around 1.3 to 1.7k rpm, and just tightening my header bolts seemed to eliminate that completely.

 

Octane provides a controlled burn so using higher octane helps to eliminate pre-ignition. If you have true knock (pre-ignition) then higher octane gas can eliminate the knock. Of course, you can't afford to drive around all the time on high octane gas so you need to solve the source of your knock (tune up). False knock will not go away by boosting octane. The knock sensor is a microphone that listens for knock. Additional mechanical noise caused by headers and RRs can be "heard" by the knock sensor as knock. The LT4 knock module was tuned to listen for a different frequency of knock as the LT4 engine came with RRs.