Car has dead cylinder, but still has fuel, spark and great compression????

[Kwattro]

My car has one dead cylinder, makes absolutely no power at all. However it still has 165psi compression which matches the rest of the cylinders, also visible spark, and fuel.

It's an SOHC engine, I was thinking maybe the lobes are wiped off the cam shaft causing the valve to always remain shut, which would explain the good compression. Although you'd think the car would make a hell of a racket with a wasted cam, and an ignited combustion cycle that has nowhere to go, in this case it's quiet.

The cars starts and runs fine otherwise, it just has that one dead cylinder. The car is an 89 Toyota Tercel with a 4cyl 1.5l SOHC carburated.

Any ideas at all? Thx

[V-8Fan]

Two things come to mind...

First, it may well be a cam lobe destroyed. But I don't think there would be any really noticeable noise because of it. If one of the valves is not opening, then you will basically not get any fresh charge into the combustion chamber at all. If it's an intake valve not opening, well, it's obvious why that is. But if it's an exhaust valve not opening, then there will be compression at the top of the exhaust stroke and hence no way for the intake stroke to suck any charge into the cylinder. So, expect no "racket".

My second thought is this: you say there is visible spark to the cylinder, and that may be so, but in order to see it you must have removed the spark lead from the plug or you removed the plug and grounded it to the frame or engine and actually watched the plug fire. Nothing wrong with that at all, except that it is much more difficult for a spark plug to fire when it's actually operating in a combustion chamber under compression. The air is a dialectric, meaning that it has resistance. The higher the compression, the more resistance there is to the spark actually crossing the spark gap. An engine under load, or even at a higher RPM range, will have varying amounts of actual dynamic compression, and a lot of times the misfire does not occur until you load the engine as such. So what happens is that there is not enough voltage delivered to the plug to make it fire (voltage overcomes resistance, and higher voltage overcomes higher yet resistance) for one reason or another.

Theoretically, when the compression gets high enough, either the plug simply will not fire, or the leads arc or you get an arc somewhere else, and you get effectively the same result---no spark at the plug. The spark gap is meant to be the weak point in terms of resistance in your spark system, meaning that if there's going to be an arc, it happens at the plug gap. But if it happens inside the distributor cap, or somewhere along the spark lead, you get no fire to that plug. So, I think you get the picture. Sorry for rambling on so badly!


EDITED TO ADD: If your idle seems smooth and is at the correct RPM, I would take a good close look at the distributor cap and rotor and the spark leads.