pletzvet

With a proper working knock sensor, is it possible or *normal* to hear the onset of pinging (i.e. - the first "ping") before the knock sensor senses it, communicates with the ECM and timing is adjusted. If yes, to the first part, does the timing get readjusted as soon as the pinging stops.

Muffin

Yes, you can hear a ping, or at least I can. EST pulls timing until pinging stops then adds it back as long as there no ping. If I recall correctly the pull and add back is in 2 degree increments.

I best add this is what I recall reading about my 85. Do not know if it applies to other years since 85 was a stand alone year ECM wise.

pletzvet

This is interesting, because I've been driving for about 40 years, I can say that I *remember* what pinging sounds like - but of course in more recent years with fuel injection and EGMs the sound of pinging is basically a thing of the past. I haven't heard an engine ping in years!

Since getting my '85 about 5 years ago, I've often puzzled over this odd noise (I kept thinking it was a slight "backfire" through the throttle body) that I hear sometimes when I suddenly put the horses into it. I'll bet now that it's the first sound of a ping.

I put a new timing set in the car last year, and set the timing to specs, but have always run just reg 89 octane fuel. Perhaps I'll try a tank of higher octane and see if that makes a difference.

69427

The knock sensor hears it before you do, in that it is listening to every bit of noise in the engine all the time. The reason you hear it is that the ESC module (not the sensor) is calibrated to not notify the ECM until the knock signal from the sensor reaches a certain amplitude and pulse width. Keep in mind that piston slap causes the same frequency pulses as knock to be read by the sensor. Also, some valvetrain wideband noises will inherently have noise in the 5kHz to 6kHz (normal knock frequency) range. It is up to the ESC module to do the majority decision work deciding whether actual knock has occured. Due to all the internal engine "background" noise, the ESC module is forced to ignore some 5-6kHz knock signals until they have grown in sufficient amplitude to be readily identified as knock, and not just mechanical noise.
Newer engines are quieter mechanically, which allows a more sensitive ESC calibration. Also, ECM software available in newer vehicles is more sophisticated and can identify at what piston/crankshaft position the noise occured at, and help to discriminate between random noise and crank angle positional knock.

aklim

I would think that the ECM should retard timing when it hears pinging. IIRC, it would drop timing by 2 degrees and then more and more till it hears no more pinging and then up it by 1 and see if it pings.

I would assume that if you can hear it, that means it is outside of the ECM range of adjustment.