The Garage Maintenance & Repair

Here’s How To Check for Vacuum Leaks and Fix Them

Nope, finding them isn't as hard as you thought.

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As your car gets older, it can begin to run, shall we say…poorly. And that’s even with keeping up with oil changes, cleaning the air filter, and throwing fresh plugs in it whenever you should. Part of that’s due to the eventual breakdown of gaskets and hoses. Vacuum leaks come with that breakdown and are just one thing that will start popping up at some point.

Dealing with the vacuum leak isn’t usually the problem, they’re fairly easy to fix even for novice wrenches. Finding them, that’s the tricky part. We’ve all been there under the hood chasing vacuum leaks while demonstrating how well-versed we are in reciting all of George Carlin’s “7 Dirty Words” set—we can recite it verbatim at this point.

Thankfully, there are many ways to detect vacuum leaks to make life easier and you’ve come to the right place. The Drive’s big-brained team is here to share a few top tips to pinpoint the source of your problems rather than springing for a new ride.

The Basics of Finding Vacuum Leaks

Estimated Time Needed: 30 minutes to an hour 

Skill Level: Intermediate

Vehicle System: Intake System

What You Need to Know About Vacuum Leaks 

First, let’s talk about what a vacuum leak is. Internal combustion draws in air and fuel with the vacuum created by the downward motion of the piston. As the piston travels downward in the bore, it draws fuel through the intake system and into the cylinder.

A vacuum leak means that air can enter the system by abnormal means or not through the induction system. No bueno. 

Air can enter the engine through faulty gaskets between the parts of the intake system, cracked, damaged, or disconnected hoses, and potentially even through broken components. 

Think about how many parts take advantage of the engine vacuum outside of just the engine. Power brakes, power steering, the PCV valve, even the climate control system in the cabin can all rely on engine vacuum. The systems that utilize engine vacuum can vary by car, but you can see how trying to pinpoint a vacuum leak can turn into a major headache.

Luckily, the vacuum system diagram is located under your car’s hood, is readily available on the internet, or in your dusty manual. This information won’t tell you where a vacuum leak is, but it will tell you all of the places you need to find one. However, we really can’t stress how important it is to research your exact vehicle’s system enough, especially if it’s been modified.  

Vacuum Leak Symptoms

When a vacuum leak is present, it creates a lean running condition. Essentially it throws off the fuel and air mixture and will impact the vehicle, though how it impacts it depends on a few factors.

Modern cars use an O2 sensor to monitor the air and fuel mixture and correct it at all times. So when a vacuum leak is present, it tries to correct the mixture by sending higher fuel levels to offset the influx of air. The result is usually a high idle.

There’s no such way for the system to enrich the fuel mixture on its own on older vehicles featuring carburetors. Instead, you’re left with a rough idle and probably find yourself correcting it by adding way more fuel than normal to try and stabilize things.

What’s important to take from this information is that finding vacuum leaks is made easy with your ears. For many of the steps below, you’re listening to changes in the engine’s running condition as you troubleshoot. 

Safety for Finding Vacuum Leaks

Any time you’re working under the hood, you need to protect yourself. But when tracking down vacuum leaks, it’s easy to lose a few fingers or barbeque yourself. So, if you don’t want to be what’s for dinner, you might want to keep these safety tips in mind.

  • Include the usual suspects. You’re under the hood of a car with a running engine. That means you want to throw on some safety glasses and gloves to protect the goods.
  • Keep your fingers clear of moving parts. The engine’s going to be running for the majority of the tests we highlight. Gloves or not, the fan and other moving parts will make quick work of your fingers if you’re not careful. 
  • You’re no different from a juicy burger. One more time: the engine is running for the majority of these tests. You’re burgers, and hot dogs might not scream on the grill, but you will if you touch the parts of your engine that get a little more than warmed up. Always be mindful of what those parts are and avoid contact. 
  • Mind your Flammables. Some of the tests involve spraying flammable fluids or gases onto the parts of a running engine. Be mindful of the risks and be sure to control the direction of these substances as best you can. 

Everything You’ll Need To Find Vacuum Leaks

You can count on getting lucky enough to find vacuum leaks with a quick visual inspection. But chances are you’re going to need a few odds and ends to get the job done. Now, we don’t know what you have on hand, but we can give you some suggestions on what tools to use.

Tool List (If Applicable)

  • Vacuum tester gauge (Brake bleeder tool with vacuum testing function is fine)  
  • Carb cleaner (Starting fluid is also acceptable) 
  • Propane torch
  • Fuel line (optional for propane enrichment test)
  • Water spray bottle 

Organizing your tools and gear so everything is easily reachable will save precious minutes waiting for your handy-dandy child or four-legged helper to bring you the sandpaper or blowtorch. (You won’t need a blowtorch for this job. Please don’t have your kid hand you a blowtorch—Ed.)

You’ll also need a flat workspace, such as a garage floor, driveway, or street parking that’s also well-ventilated. Check your local laws to make sure you’re not violating any codes when using the street because we aren’t getting your ride out of the clink.

Here’s How To Find Vacuum Leaks

We’ve broken up each test as a step in this process. As you move through them, you’ll find that all procedures work to find the same problem.

You may also notice that we don’t highlight any smoke testing. That’s simply because not everyone has a smoke machine. What we do have below are just some of the methods do it yourselfers commonly perform with items they do have on hand. 

Let’s do this! 

  1. Identify All Vacuum Lines, Tubes, and Components. The first thing you want to do is find out exactly where all the vacuum lines are on your engine. Again, your car might have a label under the hood but if it doesn’t, you can likely find that information on the internet or in your manual. If the engine’s been modified, it becomes a case-by-case scenario, and you will need to familiarize yourself with the specifics of your setup.
Vacuum diagram on 2002 Ram 1500., Hank O’Hop
  1. Perform a Visual Inspection. Visually inspect all the lines and connections to see if there are any apparent issues. A line might be disconnected, have a crack in it, or even be broken right in two. If that’s the case, you’ve found the problem.
Rotted vacuum cap on Holley carb that’s ready for replacement., Hank O’Hop
  1. Use a Vacuum Tester. Sometimes, vacuum leaks exist within complex circuits and systems that you can’t easily reach. For example, a faulty brake booster will create a vacuum leak, and you’ll have no way of telling just by looking. The good news is that the fancy device you use to bleed your brakes can be used. All you have to do is hook it up to the vacuum lines, pump it up and observe the reading. If it holds a vacuum, you can eliminate it from your list of culprits and continue to test the others.
  2. Checking the Intake Manifold for Vacuum Leaks. Unlike the scene in Fast and the Furious where a floorboard pops off due to Brian’s “Danger to Manifold”, your manifold may actually be compromised. Make sure there are no cracks or damage present or on the throttle body or carb. Also, look for any vacuum sensors on the manifold to ensure that they aren’t damaged either.
  3. Locating Vacuum Leaks with Water. You can find a vacuum leak using nothing more than water, too. When you spray water over a vacuum leak, you will hear it get sucked into the engine. It won’t affect idle much, but it can prove effective for large vacuum leaks like cracks in lines that are difficult to see. 
  4. Enrich it With Propane. Using a propane torch to detect manifold and vacuum leaks is very simple. All you need to do is open your propane torch’s valve without igniting it and run the tip along with the various gasket locations or vacuum connections. As you do this, listen to the idle. Any spikes in the RPM are due to the propane entering the combustion chamber.
Introducing propane to manifold gasket on 440. The same procedure applies to any engine., Hank O’Hop
  1. Carb Cleaner Test. This procedure closely resembles the propane enrichment test as you’re introducing a flammable substance to each connection. The process is pretty much the same. All you do is identify where the gaskets are and spray some carb cleaner while listening to engine speed. If you perform this test, you need to be careful. The stream of carb cleaner is not as controlled as using propane. While this is one of the most common methods DIYers use, there is a risk of accidentally spraying a surface that’s hot enough to ignite the cleaner.
Just like propane, carb cleaner (starting fluid in this case) is introduced to gasket surfaces., Hank O’Hop

What if My Engine Doesn’t Power Vacuum-Operated Systems?

Your car might do away with options like a power brake system. A previous owner might have hopped the car up and ditched anything that wasn’t necessary. Or maybe, the engine build doesn’t create enough vacuum to power those components, so an electric vacuum pump was utilized.

We should also add that a lot of modern engines even feature a belt-driven vacuum pump to assist the brake system.

In any case, you’re subject to a bit of a different process. If no vacuum lines are coming off the engine, only faults between the intake system’s mating surfaces, or the components themselves, can be the source of a vacuum leak. To Inspect these surfaces, you’ll want to implore the propane enrichment or carb cleaner tests listed above if there is no obvious damage.

If you’re running an auxiliary vacuum pump, issues with the vacuum lines won’t cause any problems for the engine’s running condition. Instead, only the systems operating on that vacuum power will suffer. For example, suppose the connection between the power brake booster is the problem. In that case, your brakes will be as hard as a rock as there’s not enough vacuum to assist the system—yet another reason addressing vacuum leaks is so important.

To determine where the issue is located with this type of system, usually, a visual inspection is all that’s necessary. However, you may also need to use the vacuum pump test to inspect the condition of the systems that are relying on vacuum.

What About Forced Induction?

Your car might very well have a turbocharger or supercharger on it. In that case, rather than relying on vacuum, the engine uses positive displacement pumps (superchargers or turbochargers) to force air through the intake system.

It can be easy to overthink the scenario and conclude that the steps listed above won’t work for your setup. And to an extent, that is true. Finding leaks in a forced induction system requires special testing tools and procedures.

However, anything after the throttle body or carb on cars with superchargers can be tested with the same procedures as the engine still produces vacuum at idle, just like a naturally aspirated engine.

Sometimes You Need a Certified Mechanic

As much as The Drive loves to put the “you” in do-it-yourself, we know that not everyone has the proper tools, a safe workspace, the spare time, or the confidence to tackle major automotive repairs. Sometimes, you just need quality repair work performed by professionals you can trust like our partners, the certified mechanics at Goodyear Tire & Service.

Pro Tips to Finding Vacuum Leaks

Here are The Drive’s pro tips.

  • You might be able to hear vacuum leaks. It can be noisy under the hood, but vacuum leaks make a distinct whistling sound. If you listen carefully, you may pick up on the noise and trace it to the source.
  • As an alternative to the vacuum gauge test, you can try to pinch the vacuum lines by hand while the engine is running. In doing so, you’ll find that the idle improves when the faulty component is disconnected from the manifold.
  • Make sure your manifold is on tight. If you’ve recently installed an intake manifold and are experiencing start and run issues, don’t be too proud to go back and double-check your work.
  • When performing the propane enrichment or carb cleaner tests, you really want to be careful. These are the two preferred methods to detecting faulty gaskets because of how conclusive they are, but you are introducing flammable gases under the hood of a running car. So, be mindful of hot surfaces and be sure to avoid them as you can cause a major fire.
  • It doesn’t need to be carb cleaner for the carb cleaner method. Starting fluid or any other flammable liquid will also work.
  • The propane enrichment test is preferred over the carb cleaner test for a reason. That’s simply because of the higher level of control you have over the flow of propane gas. To take things a step further, you can attach a flexible hose to the end of the nozzle for even better control in tight spaces.

FAQs About Vacuum Leaks

You’ve got questions, The Drive has answers!

Q: Is It Bad to Drive With a Vacuum Leak?

A: The short answer is yes. Vacuum leaks can impact several essential systems and rob your engine of performance. Even if the car moves under its own power, you really shouldn’t proceed if it has a vacuum leak.

Q: What Can I Spray to Check for Vacuum Leaks?

A: Any sort of flammable liquid can be used. Carb cleaner, brake cleaner, starting fluid, and propane are all commonly used for the process as they will increase the engine speed when they enter through vacuum leaks.

Water can be used as an alternative as it will create a distinct sound when it is pulled into the engine through a leak.

Q: Can I Use WD40 to Find a Vacuum Leak?

A: Yes. You can use regular WD40 to detect vacuum leaks. The impact it has on the engine may not be as dramatic as carb cleaner or starting fluid, but it will still work. Keep in mind that WD40 does offer carb cleaner, which is ideal for this test. 

Q: Is a Vacuum Leak Expensive to Fix?

A: the price to fix a vacuum leak depends on the source. Broken hoses and tubes rarely run more than a few dollars to replace. However, the cost to replace an intake manifold, sensors, and gaskets can tally up the total investment quickly.


Learn more about finding vacuum leaks with this helpful clip.

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Hank O'Hop Avatar

Hank O'Hop

Associate Editor, Commerce

Hank is an Associate Editor at The Drive. He may be here to recommend tools and parts, but he’s always happy to dive deep into tech discussions, especially when it gives him the opportunity to display his old Dodge.