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Diagnosing Vacuum Leaks 101 How to Find Leaks and Fix Them

Diagnosing Vacuum Leaks 101 How to Find Leaks and Fix Them

When most people think of modern car engines, they see this massive system of advanced electronics, complicated software controllers, and sensors working in unison to deliver efficient power. While that’s not too far off base, a good portion of the heavy lifting when it comes to controlling various systems is done by vacuum. The best way to understand just how important the vacuum is for a modern car engine is to experience a vacuum leak. Vacuum leaks can be tricky to diagnose, especially if your car runs a complex vacuum system. That being said, there are ways to recognize the symptoms, diagnose the problem, and make repairs where necessary.

The Power of Vacuum

A vacuum is a powerful tool that was recognized as such by the automotive industry a long time ago. The lack of air was the answer to so many engineering problems where otherwise, popular mechanical solutions simply couldn’t help. As a result, your average engine is covered with vacuum hoses running from one system to another.

Some of the things that wouldn’t run without vacuum include your turbocharger, the heating element, the AC, the intercooler, and even your brakes, depending on the car. From function-critical systems to pop-up headlights, the vacuum is the solution.

SAAB 900 Recognizing the Symptoms of a Vacuum Leak in the Engine

The Good and The Bad

Just like with anything else, there are good and bad sides to vacuum systems. The main drawback of using a vacuum mainly has to do with the delivery system. Hose used to run the vacuum around the engine are just that – hoses. As we know, rubber is probably the least durable material you can find in an average engine.

As time goes by, almost all rubber hoses will start to deteriorate. We can attribute this to age alone, but the engine’s heat/cold cycles definitely add to the problem. When rubber hoses begin to go one by one, you’ll start having leaks all over the place. Some leaks are easy to find, but some aren’t.

Tracking down a subtle loss of vacuum can be akin to searching for a needle in a haystack. Sometimes we’re lucky, and the gods of wrenching treat us with an aggressive, hissing leak you can hear from 5ft away. Those are easy. It’s the slow, silent leaks that you should worry about.

So how do you deal with those? First, you’ll need to recognize the problem.

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Recognizing the Symptoms of a Vacuum Leak in the Engine

Vacuum leaks are interesting in the sense that they can cause all kinds of trouble. However, the most common type of leak involves the air ingress after the mass airflow sensor in your car. Even a small leak anywhere in the intake manifold can be an issue.

Your mass airflow sensor serves an important purpose. It’s there to measure the amount of air that’s going into the engine. That information is then used by the ECU to calculate the right air/fuel mixture and deliver that to the cylinders.

By having air entering the system that’s unaccounted for, the air/fuel mixture will never be correct. As a result, you’ll experience one of the most common symptoms of a vacuum leak – the rough or high idle. Which one of these will happen mainly depends on how the ECU decides to compensate for an increase in air values.

A more severe symptom would be stalling at low RPMs. This may or may not be followed by an intermittent drop of power as you’re driving along, resulting in a jerky throttle. The worst thing about this type of leak is that it often sends people on a wild goose chase.

Now that you know the most common symptoms, let’s go over a few simple ways to find vacuum leaks in your car.

Recognizing the Symptoms of a Vacuum Leak in the Engine

Start With the Intake

As it just so happens, most of the vacuum lines on an average engine run from the intake manifold and spread to different places. However, it’s don’t ignore the intake itself. If you were to pop the hood on most modern cars, you would find that a large portion of the intake system is made of rubber or plastics. Especially the part that leads to and from the mass airflow sensor.

Those rubber parts are prone to cracking over time. Start your search by checking everything from the sensor leading into the manifold. Make sure to check the bottom side of the tube as well. If everything’s fine there, move on to the smaller lines on the manifold.

These generally crack around the connection points as that’s where they’re stressed the most. A visual inspection often reveals a leak fairly quickly.

Listen for The Leaks

If everything is alright visually, try to listen for the leak. We’ve mentioned that some can be really loud. That depends on the extent of the puncture. If a hose is completely severed, you’ll hear a strong hissing sound coming from the engine bay. You can always ask someone to apply some throttle while you’re close to the engine.

Those who need a reference point for the sound’s intensity and volume can simply remove one of the healthy hoses. If the puncture is terrible enough, it will sound like a removed hose.

Look for the Bubbles

We’re not often blessed with loud, easy to find leaks. In many cases, you’ll be dealing with a tiny leak that might make you question your sanity for a brief moment. Locating tiny holes in hoses can be a pain. Such leaks are silent, often just large enough to disrupt the engine and not much more.

To find such leaks, you’ll need a spray bottle and a little bit of dish soap. Make a rich mix and spray all of the fittings, and areas you’re suspecting might be where the leak is at. Once you’ve applied the soapy water, get the system’s pressure up by getting the RPMs up. It’s best to have a helper do this for you. With the RPMs high (a 1,000RPM above idle is enough, there is no need to redline it), look for bubbles in the areas you’ve sprayed.

Additional locations of interest include intake manifold gaskets, brake booster, EGR valve, and the PCV valve.
Fun fact, you can use this very same trick to find where your tire is punctured.

How to Check the Brake Booster and PCV Valve?

Figuring out whether or not your brake booster might be causing the issue is quite simple. It comes down to first testing the vacuum hose that leads to the brake booster assembly. If that hose is solid, simply take a pair of pliers and pinch it in the middle.

Doing so will cut the brake booster from the rest of the vacuum system. If you notice a change in the RPM as you do this, you’ve got your culprit! The same applies to the PCV valve – check the hose that leads to it, and then pinch it to check the PCV valve.

Make Sure to Look for Leaks on a Cold Engine

Everything we’ve described so far will work best if applied to a cold engine. Once you start a cold engine, the mass airflow sensor dictates the air/fuel mixture. In case of a vacuum leak, you’ll get that notorious rough idle and other symptoms. However, if you let the car warm up, the O2 sensors and the ECU will eventually compensate for the leak and make finding the culprit a bit more complicated.

Preemptive Maintenance Tips

The absolute worst thing about vacuum issues is the chance that you’ll be chasing phantoms for a while. This is especially true for older vehicles that are slowly getting to a point where most of the rubber components are well deteriorated.

One of the solutions is to do a preemptive replacement of all rubber hose. If you decide to do this, you’ve got two options – you can either go with the OEM replacements or get an aftermarket silicone hose kit. Silicone has been the go-to choice for most aftermarket mods as it doesn’t suffer from the same problems as rubber. It is much better at handling vicious heat cycles, and it won’t go brittle on you.

Besides, most of these kits come in all kinds of awesome colors, leaving plenty of room for you to do some visual tuning of your engine bay.

How to Find the Right Vacuum Hoses for Your Car?

To find the right hoses for your car, all you have to do is head over to our online store and input your car’s year, make and model. Our system will show you all of the parts that match your input, including our selection of vacuum lines. In case you have any questions about our offer, you can always get in touch with us by contacting our customer support. We’re standing by to help!

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