How Your Car's Engine Works

Something Novel

Mar 13, 2021

A few months ago, driving early on a cold morning, my engine started running strange and my check engine light popped on. A pitstop over to an AutoZone and 5 minutes with their OEM reader told me that I was getting a misfire on cylinder 3, 5 and 6. Usually a misfire in a cylinder is caused by one of two things, the spark plug or the ignition coil.

Not sure which the issue was in my case, and being due for it, I ended up getting eight new spark plugs and eight new ignition coils to replace the two parts in each of the eight cylinders for my vehicle. While waiting for the parts to come in, I realized I didn’t actually understand what they did or why they caused my issue, so I set out to find out. Here’s what I learned —

How an Engine Works

Your car might have four, five, six, eight or more cylinders. However many it does have, in each, the same four step process is firing usually around three thousand times per minute. You can reference my mediocre drawing above or you can find a more comprehensive schematic here.

Air and fuel enter the combustion chamber near the top of your cylinder through the intake valve. The piston is in the intake position to create room in the chamber for the mixture.
Intake valve closes. The crankshaft rotates to compress the mixture in the combustion chamber.
The spark plug fires, igniting the mixture and pushing the piston down. This is called the power stroke that drives the crankshaft.
The exhaust valve opens, the piston rotates back up to push the exhaust gas out of the chamber.

To my situation above, in 3/8 cylinders, either my spark plugs were not firing, or my ignition coils which sit above the spark plug were not providing the electricity to the plug to fire.

My lowest shop quote to replace just the three was $800, done in 3 days from drop-off. The parts came in to replace all eight for $220. All the work was done w/ a $40 ratchet set and a couple flat head screwdrivers in about 2 hours. I don’t make $300+/hour yet, so the endeavor was well worth my time.

Problems aren’t as spooky when they’re understood. I was reading a book I’d highly recommend at the time that encouraged me to look a bit deeper at the logos of the world(Opposite mythos). — Zen and the Art of Motorcycle Maintenance.

Next week, I’m going to talk about the things that incentivize us and this thing called the daemon.

Enjoy the details.

-Benjamin Anderson