ckdenion
Tested kenjilew's car before, the car starts normally, drive normally, whack normally, wheel spun normally. Siuyi also whack his car. So its not the 2 sepakberak not functioning, its burning lean.

My speculate is, due to 3rd & 4th piston is running lean, GaGa eversosmart Continental ECU will retard ignition timing to avoid over burn(lean burning), hence his 1st & 2nd sepakberak emit brownish dust. Usually a healthy engine, all 4 sepakberak white insulator will turn brown, but not to the extend of emit powder. Meaning now his 1st & 2nd have excess fuel unfinish.

Injector sumbat oso got 2 type, 1 is RICH, another is LEAN. Ayam 1 of the victim of not usual type of RICH sumbat, residue stuck on the nozzle, injector unable to shut properly. Very hard to start car, drive fast will emit black smoke like hutan bakar. It can cause chain reaction as excessive carbon will block the CO sensor, and ECU sense too little emission and think its running lean, inject more fuel to the already sumbatted injector, more unfinish burn fuel more hutan bakar to the extend the car will lose power. This type of sumbat will create a lot of carbon residue inside the engine, but generally it does not create physical harm. If this happen, 1 have no way not to send for service immediately. Can find my post in the early V21 or V22 when I kena that time.

I suspect kenji's car is on the usual sumbat LEAN. This is usually the slow death sumbat. It sumbat you don't know. The car still run perfectly fine, until 1 day the gasket giveup on high heat generated by lean burning process. This type of sumbat usually can caused by residue stuck at the injector nozzle's opening. Fuel weren't able to deliver as expectation. Usually experienced magician will use a high frequency shaker to vibrate all the dirt out from the injector, then force the nozzle to spray alcohol for cleaning purposes.

Set all those aside, here's the simple answer for your lean/stoich/rich theory. Ever went for Chemistry/Genral science during high school? Teacher will lite up a josstick, put it in a pure oxigen tube. The josstick that almost gonna lesap suddenly become big fire ball. This is lean burning. Fuel is the josstick, excessive air in the tube empower the fuel being burn efficiently. However, the same almost lesap josstick, when you throw it in a tube of petrol, what will happen? It will just goes off. In this case, petrol itself is a coolant.

In any of the car designed, their engine is tuned to slightly rich. Fuel itself despite is the core of burning, but it plays an important role for cooling DURING the burning process. SR-71 bomber/recon jet, the fuel can last up to 300'c, and its the coolant for the hydraulic system itself.

You may wiki STOICH to find out more. I can't give the link now as ayam on mobile, not convenient to go surf around.