The octane thread got me thinking about pre-ignition vs. detonation.  My truck, a 93 toyota with the 22-re engine with 192k miles on it, 'pings' under what I would consider a higher load condition (in 5th gear climbing grades while trying to accellerate under mid to full throttle situations).  I run mid-grade fuel and this seems to reduce the problem.

The question is how can I tell if it is pre-ignition problem, which I understand to be hot spots of carbon igniting the fuel prematurely, or, detonation, which I understand to be heat/pressure from the advancing flame front igniting the remaining af mix before the flame front reaches it causing high pressure peaks and unsmooth combustion? 

Once I find this out, what are the best ways to alleviate this?  Patprimmer suggested a water spray treatment into the throttle under a power run.  Is that a WOT condition, or what?  How much water?   Is there a better way to clean the combustion chamber?

7.7 What is the effect of engine deposits?
A new engine may only require a fuel of 6-9 octane numbers lower than the same engine after 25,000 km. This Octane Requirement Increase (ORI) is due to the formation of a mixture of organic and inorganic deposits resulting from both the fuel and the lubricant. They reach an equilibrium amount because of flaking, however dramatic changes in driving styles can also result in dramatic changes of the equilibrium position. When the engine starts to burn more oil, the octane requirement can increase again. ORIs up to 12 are not uncommon, depending on driving style [17,19]. The deposits produce the ORI by several mechanisms:-

- they reduce the combustion chamber volume, effectively increasing the compression ratio. - they also reduce thermal conductivity, thus increasing the combustion chamber temperatures. - they catalyse undesirable pre-flame reactions that produce end gases with low autoignition temperatures.

I prefer the lsat explanation rather than hot spots.

Water is the best way to clean the combustion chamber without disassembling the engine.

I'm sure a garden hose/washer pump will work.  We always use a two liter soda bottle filled with water.  With one guy running the engine at WOT, we pour in enough water where the engine starts to cough, then back off pouring the water.

Doing this (or the hose, or the washer pump) will do wonders.  Just be sure the engine is warm when you do it.

You might try some stuff called SeaFoam, sold alongside the Marvel Mystery oil.  I'm always skeptical of snake oils but I have found it to be great for specific tasks.  

When added to the oil about 100 miles ahead of an oil change, it will remove noticeable amouts of gum/varnish from oil control rings (the Saturn people turned me onto this, Saturns have a known problem with their oil rings pre-'99, one treatment has cut my oil consumption by 50% for the last 5,000 miles).  

If you pull the spark plugs and pour a tablespoon into each cylinder and let soak/drain overnight, remove any left in the chamber by cranking with rags over the holes, then fire it up "briskly" (mucho smoke!) and drive aggressively for 15 minutes, it will burn off/flake off/get rid of noticeable amounts of build-up on the pistons.  Adding it to the gas can accomplish the same thing in a much slower but less smoky fashion, and apparently also helps get rid of valve head deposits.

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