Join Date: Jan 2006
Location: Columbus, IN
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Firstly, as a bit of technobabble, there are two kinds of pinging: detonation (somewhat OK) and pre-ignition (holy pistons batman!). Detonation is somewhat normal on an engine putting out a lot of power especially if it's in lower rpms (IE climbing a hill loaded w/o downshifting). Pre-ignition is sort of the extreme version of it. The difference is that detonation is a second flame front igniting AFTER the spark sets off the primary (remember gasoline isn't exploding in the combustion chamber, it's a controlled burn). Pre-ignition is when conditions are right that the mixture ignites before spark occurs. This causes a build up of pressure while the piston is still rising and is how you melt rings, blow holes in pistons or head gaskets, and generally destroy an engine.
Either one can be caused by high compression/low octane for the compression ratio, glowing carbon, etc. lean mixtures makes it more susceptible which is part of the reason cars run rich at WOT...just to be sure since there's so much noise the knock sensors not as reliable.
the knock sensor sends a voltage signal to the ECU and yes, the ECU pulls ignition timing: that's it.
I usually think of it as sounding like shaking a spray paint can after the paints all gone and the ball's just bouncing around.
As far as why some do and some don't, a lot of it has to do with lots of people not knowing what to listen for and some people calling loose valves or bearings pinging. also, as with any 20+ year old engine design, some have been rebuilt, some more than once. shaving the head and/or block will raise compression which increases the tendancy to ping. Could also be one injector running rich or another running lean throwing off the mixture for the others (lean running ones start to ping, others are OK). or differences in compression. Quality of gas will affect it too. running hot, EGR ports plugged, increased ignition timing all contribute.
"You don't get to judge me for how I fix what you break"
'94 Pontiac Firebird LT1, T56
'90 Cressida, 7M-GE, M5
'91 Toyota Pickup, 22R-E, M5, 2wd