Auto Mechanics

Have you ever been driving along happily, minding your own business, when all of a sudden your car starts making some strange noise? Maybe a smell, some smoke, or a strange vibration? And then you're stranded on the side of the road. I've been there, and I assume most everyone with a car has.

Back in the day, the engine was a veritable mystery box to me. So when I'd pop the hood to see what the problem might be, if the engine was still there I'd be at a loss. So it'd be a phone call to a buddy to bail me out, or if I was really unlucky, a tow. Well, I'm here to tell you that it's helpful to know a thing or two about these metal buckets we ride around at high speeds.

Now, like just about anything, we could dive real deep into auto mechanics. There are a breadth of valuable topics, from suspension to timing to exhaust management to performance enhancement to air conditioning. However, we are going to talk in broad strokes and try to cover some things that'll help you make a basic diagnoses of auto problems.

Your car engine needs three basic things to run: air, fuel and a spark.

Air

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In a modern vehicle, air is drawn in through a filter, measured by a mass airflow sensor (MAF) and mixed with fuel to create the explosions that produce power. When you press the pedal in your car, the air throttle opens and allows more air air in, which causes more fuel to be injected, increasing the power generated. This is done through the air intake manifold, which typically covers the very top center of your engine.

Air is drawn in by a vacuum created by the action of the cylinders in the engine. One common problem here is a vacuum leak, meaning that excess air is being drawn in form an imperfect seal or a hose with a hole in it. This causes the air-to-fuel ratio to be off, (in this case, the car would be running "lean") leading to a rough idle or in bad cases, a non-start. Another common problem with air is the sensitive MAF, which can report incorrect amounts of air entering the engine, again leading to a incorrect air/fuel ratio.

To diagnose a vacuum leak, a visual inspection of the various vacuum hoses and air related components can be performed. If suspected but not found, a nifty trick is to light a cigar and let the smoke near the intake manifold and related hoses, and see if the smoke in sucked in at any point. To diagnose the MAF, you would simply unplug the electrical connector to it and see if/how the engine performance changes.


Fuel

http://www.boltonautorepair.com/images/diagram_fuel_engine.jpg

Fuel (in our case, gasoline, as diesel cars are less common and function slightly different) is pumped from the fuel tank into a fuel rail, which then sprays into the cylinders via fuel injectors, along with the correct amount of air.

Several problems can cause improper fuel delivery. The fuel pump might quit, the fuel filter might clog, the fuel injectors might cease to deliver proper (or any) amounts of fuel. Fortunately, these are fairly easy to diagnose.

The first test for fuel delivery is to check fuel pressure. This is easily done, as there is a schrader valve (just like a bicycle) on the fuel rail. Simply depress the valve and see if a short plume of fuel sprays out (don't lean too close). If not, the fuel pump may be faulty or there may be a break in the fuel line somewhere (this would manifest in pools of fuel underneath the car).

Another quick test is to prime the engine (that is, turn the ignition to "on" but don't crank), you should hear the fuel pump come on and pre-pressurize the fuel lines. If you don't hear anything, try having someone else turn the key while you put your ear near the fuel tank. Typically, a no-start related to fuel would be due to a malfunctioning fuel pump, which might be a mechanical or electrical issue.


Spark

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To cap it off, once the proper air/fuel mixture reaches the cylinder, a spark is needed to set it all off. This comes from the spark plug, which receives electricity from either a distributor or coil pack. Unfortunately, while diagnoses can be simple, it can also be rather dangerous so I will refrain from offering hints.

Misc

Now, there are plenty of other conditions that can result in a no-start or rough ride, and I'll briefly touch on a couple common ones.

Head Gasket

If an engine overheats (due to perhaps a loss of coolant, or poor radiator performance) then a likely and common result is a blown head gasket. The head gasket provides the seal between the engine block (lower part) and the cylinder heads (the top part) of the engine. A malfunction here could cause cross-contamination of oil and coolant, exhaust leaking into the coolant, or loss of compression to one or more cylinders. 

http://gobdp.com/blog/what-are-the-symptoms-of-a-blown-head-gasket/

http://www.agcoauto.com/content/news/p2_articleid/200

Starter
Another no-start condition is a starter failure, The starter in a car is a mini-engine that is powered by your battery. When you turn the key, the starter bendix pops out and connects to the flywheel and turns the engine with enough force to make the air intake/fuel mix/spark cycle to begin. When you need a jump, it's because your battery doesn't have enough juice to power the starter. This might be a sign of a bad battery, bad alternator (which charges the battery) or a forgetful driver that leaves their lights on. Starters can also fail, but more commonly the battery is at fault.

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Conclusion
Hope you came away with a better understanding of your cars engine. I really do encourage you to pick up a wrench next time something is wrong, it's not as hard as you'd think to patch an engine, and you can save a bundle. Plus, the knowledge will be useful in our post-apocalyptic mad max future!