Ballistic Spark Plugs

Wot's that flying out of my hood, then?It's another one of those stranger-than-fiction stories, this time from the automotive world. I was on the highway only a few miles from home, when suddenly there was a loud pop. It was the kind of thing you could feel; my first thought was one of the tires had blown out. There was a loud thumping sound, which at that moment seemed to have the same timing as the rotation of the wheels. So I pulled over on the shoulder, which was where I noticed a strong smell of gasoline. The thunking noise was still there, so this obviously hadn't been a blowout after all. Possibilities were racing through my mind: I envisioned a fuel line flopping around under the hood, spewing gasoline on the hot manifold. Throwing caution and common sense to the wind, I decided to go for it instead of turning off the engine and leaving the car on the highway. Only a couple miles to go, I thought, and if the engine compartment erupts in flame, at least I won't have far to walk.

Keeping my foot on the accelerator so the engine wouldn't stall, I eased the car back onto the highway. The engine was loud—at least as loud as a four-cylinder engine gets. It sounded as though it had lost part of the exhaust system; I thought about the exhaust manifold hanging by a thread, or by a bolt, maybe. I knew this was unlikely in the extreme, but my brain was working through every scenario. I had to stop at a traffic light, and every head turned at the obnoxious sound coming from the little engine. When the light turned green, I managed to get the car moving again. It didn't seem to have much power left as I coaxed it to 45 mph for the remaining mile or so to my house. Shifting to neutral, I was able to keep the engine running with my right foot while I rolled into the driveway and stopped the car with my left. The smell of gasoline had, by this time, turned into the smell of exhaust. I killed the engine and pulled the hood release, reluctantly, not really wanting to know what I might find in that engine compartment.

This is where I should have called the guys at Car Talkit might have made a good puzzler for them—but I didn't. Under the hood everything looked normal—no gasoline or other liquids washing over the engine block. Both manifolds appeared to be where they had always been. It was then I noticed a subtle discoloration on the underside of the hood. A wet spot, sort of, which pointed to one of the four spark plugs on top of the engine. Sure enough, one of the rubber plug-wire covers appeared to be slightly out of place, and I pulled it away with less effort than should have been required. I peered into the hole where the spark plug lives, but it was like looking into a well; I couldn't see the bottom. When I got a flashlight and looked again, there was nothing in the hole at all. The spark plug was gone! This struck me as odd, because generally spark plugs don't just disappear. Sometimes they break in half, and sometimes they just stop sparking, but they don't just go away. And yet, that's exactly what this one had done. With the flashlight illuminating the bottom of the hole, all I could see was the inside of the cylinder, or at least as much as one can see through that tiny spark plug hole. The plug was nowhere in sight.

Gradually the situation became clear. The sharp noise I had heard was the sound of the spark plug being violently ejected from the engine and slamming into the underside of the hood. The discoloration was the result of the spray of fuel and exhaust that had erupted from the cylinder after the spark plug left. Strangely, the plug wire was still intact and didn't appear to be damaged; the ballistic plug had somehow disconnected itself from the wire without destroying it. At this point, the questions became (1) why the plug had been violently blown from the engine, and (2) whether there was anything left of the threads that had, at some point, held the spark plug in place. It didn't seem likely that the plug had worked itself loose—literally unscrewing itself—over the course of the previous year. Had this been the case, there should have been a noticeable decrease in performance, but there wasn't. Up to the point of plug ejection, idle had been smooth and acceleration had been normal; there had been no apparent change in the engine's operation.

When my mechanic arrived later that evening with a set of spark plugs, the comedic quality of the situation wasn't lost on him. It isn't the sort of thing you see every day, but then, this car is notorious for its bizarre problems. Jettisoning a spark plug, to him, was even funnier than the complete disappearance of every impeller blade in the water pump he had changed at about the same time last year. But as it turned out, nothing was damaged and the little car now has four new spark plugs. Evidently the plug had, in fact, simply worked its way out of the engine over time; I'm not mentioning any names, but I think someone forgot to properly tighten it in the first place. I'm lucky because escaping spark plugs don't always leave things in good order when they go; a cross-threaded plug, for example, or damage to the head wouldn't have been out of the question. So, for now, the little car lives on, but I can hardly wait for the next—and no doubt surreal—automotive adventure.


No comments:

Post a Comment