I use a Snap-On scanner for T&T on my 87' GN.
At an idle the scan tool says "yes" for knock, but at WOT there is no retard. I have certainly heard knock on occasion but the Snap-On tells me otherwise. I beleive I may have read that the knock feature is a problem for the Snap-On scanners? I thougt it may have been one of the chips I was using, but they all register yes for knock. Reason is I want to get a knock gauge, but I am not sure it will work if I am getting conflicting readings. HELP
Ken, I will dump the Snapper and buy the Turbolink if you help me figure this one out! ( I was going to get one anyway
Hmmmm ... I wonder if all they really are looking at is the ESC counts. The knock sensor can register "events" and the ECM may or may not choose to retard timing in response.
Basically, the ECM filters the knock signal and decides, based on duration and load whether to retard timing or not.
There's nothing explicitly in the datastream that says "Knock" from my experience.
Thank you for your reply Ken. If this sheds any light the display on the scan tool looks something like this. ( forgive my ignorance. i'm sure you have seen one )
KNOCK....YES.............RETARD (in degrees)...0
Sometimes even at full get out there is no retard.
I just want to make sure I do not blow this engine. I have never seen the tool register NO for the knock.
Bruce Plecan wrote this on the mailing list:
Actually the ESC module does the filtering and frequ check.
The ecm is really in repitle brain mode, with if there is a voltage (or lack of) at pin so and so, I'll drop timing hoping to restore the input to the previous state. The ecm has attack and decay rates for responding, and then returning to normal.
Bruce
So basically, KNOCK = YES probably just indicatest he ESC is counting up and RETARD = 0 means that the ECM doesn't think it is a significant event.
I am having the same situation with the snap-on scanner,only in feild service mode.If I put it in daignostic mode it say no for knock and if I take a cresent wrench and tape on the rear of the intake it say YES and retards the timing.So that verifies its working properly.
Ok guys time to get a TR specific scantool.