Combustion engines rely on air to function properly. Air is drawn in to mix with gasoline for the proper combustion through the intake manifold. Since the amount of air is regulated, it creates a vacuum, which is then used to control emissions, power windshield wipers and even make it easier to brake. Vacuum hoses run from the intake manifold to the equipment that relies on the air pressure to run, which also includes automatic transmission, the distributor and the power brake booster, as can be seen on nearly any classic muscle car.
When emission control really kicked into high gear back in the 60s, some cars had dozens of hoses, which increased the risk of leaks. If a vacuum hose is damaged, resulting in a leak, this can not only activate that pesky check engine light on the dashboard, but it can increase emissions. If you are planning on taking your car for an inspection soon, and you have a leaky vacuum hose, chances are that you could fail the inspection due to high emissions. Plus, since the vacuum hoses are responsible for the operation of so many different components of a vehicle, a leak can diminish performance.
So how do you determine if there is a leak? Well, the first step is to get your hands on a hose diagram. Some vehicles may have this mounted right in the engine bay, but if not you can consult your owner's manual or look up the information online.Having a copy that you can write on will make it easy to keep track of which hoses you have checked, as there may be a lot to remember, depending on the type of vehicle you own.
The first thing to check is the connections, where the hose meets the intake manifold and the other end. Make sure that the hose fits properly at each connecting point. You should also inspect the hoses themselves for signs of visible damage and ensure that they are pliable.
Some leaks can be so small that they are not visible to the human eye, but even a hole that is less than 0.02 inches long can be detrimental to your vehicle's performance. If you spot a leak in one hose, you ought to have all of them replaced, as damage on one of the tubes could mean that the others are rapidly reaching the point where they can be susceptible to damages as well.