If you’re replacing a spark plug and you don’t tighten it enough, it will work itself loose and fail to deliver a spark. If you over-tighten a spark plug, you can strip the threads or crack the plug. Similarly, parts that have gaskets can leak if the bolts that hold them aren’t tightened enough. But if you over-tighten the same bolts, the gaskets will be crushed, causing the fluid to leak anyway.
An adjustable wrench, sometimes called a crescent wrench, is a useful addition to your toolbox. You probably already have one in the house, and you can adjust the jaws to fit a variety of nuts and bolts simply by turning the wheel. I like the very small and medium sizes because they fit into tight spaces easily.
The ECU is the most powerful computer on modern vehicles. It uses a variety of sensors to monitor and control most of the engine functions, including the electrical, fuel, and emissions control systems. Among other tasks, the ECU controls the fuel injectors on fuel-injected engines; fires the spark plugs; and controls valve timing, the fuel/air mixture, battery charging, and even the cooling fan.
It’s the key to diagnostics that pinpoint problems and is primarily responsible for managing the fuel efficiency and performance of your vehicle. If the ECU malfunctions, it usually needs to be replaced.
What Makes Your Vehicle Start?
Although people tend to think that most vehicles are totally powered by fuel, many parts — the radio, headlights, air conditioner, windshield wipers, power seats and windows, clock, and so on — actually function on electricity, which is provided by the electrical system.
The electrical system includes several subsystems that provide your vehicle with that vital spark that makes it start, keeps it running, and powers all electrical devices. It’s one of the many systems on a vehicle that’s monitored and controlled by the ECU (see the previous section).
The ignition system
A muffler controls the noise of the escaping gases; if it fails, you can get a ticket, probably for disturbing the peace! A muffler also has an effect on the pressure required to pass the exhaust gases through it: It creates the “back pressure” that the engine requires to run efficiently and affects the temperature and therefore the efficiency of the catalytic converter.
What Makes Your Vehicle Stop?
Still with me? Good! Now all you need to know is what goes on when it’s time for your vehicle to stop. This is the job of the brake system (but you knew that, right?).
Four-wheel disc brakes are standard on most new vehicles. Other vehicles have disc brakes on the front wheels and drum brakes on the rear wheels. A few older vehicles have drum brakes all around.
Now that you have a general picture of how the various systems in your vehicle work together, don’t stop here! The rest of this book goes into detail about each of the systems outlined and what you can do to repair them and keep them running smoothly. Be sure to read the chapter on how a particular system works before tackling the related instructional.