When you hear about a vacuum leak in a car it may be confusing if you're not very familiar with exactly what goes on under the hood of your vehicle. Your car obviously doesn't have a vacuum the way most people understand what that word means. In fact, what a vacuum leak refers to is the system that exists between the engine and the mass airflow sensor that controls the flow of air through your engine. Depending on where the leak is in your vacuum system the repair cost can range from as low as about $150 to as much as $1,000.
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As you know, your engine requires not just fuel but oxygen to maintain a combustion reaction. Fuel and air are injected together into the combustion chamber where a spark ignites it and causes the combustion reaction that powers your whole vehicle. This air has to flow through the vacuum system in a very controlled and precise way, just like the fuel flows through the fuel system. So, when the vacuum system springs a leak, you're going to need to get it repaired or suffer some performance problems as a result of having poor airflow.
There is an extensive range to these repair costs because the vacuum system in your car isn't just one single part. It won’t fail like a camshaft position sensor or a brake pad will. You could have a leak anywhere from the EGR valve to the positive crankcase ventilation system to the intake manifold and beyond. Figuring out where the leak is located is absolutely required in order to figure out what kind of repair job you are going to have to pay for.
What is a Vacuum Leak?
As we said, air flows through the vacuum system to get into the engine as part of the air-fuel mixture that allows your car to function. A leak in the system is a leak that occurs anywhere between the engine in the mass airflow sensor. Because your car's computer, the ECU or the PCM depending on what your make and model refers to it as, calculates the amount of fuel to inject as well as the amount of air that's needed, a leak in the vacuum can throw this off. Leaks can cause a lack of proper air or excessive air to enter the combustion chamber.
Typically, what happens in this situation is that your computer is not able to properly calculate how much fuel is needed so you end up burning what is called a lean mixture. That means you have more air and less fuel than is necessary.
Signs and Symptoms of a Vacuum Leak
There are some definite signs to be on the lookout for it to let you know that you have a vacuum leak somewhere. Though these signs don't necessarily guarantee that you have a vacuum leak there's a good chance that that's what's going on if you're experiencing any of these. If you're experiencing several and definitely consider this a high likelihood issue.
Hissing Sound
Because a vacuum leak is literally a leak in an enclosed air system the sound it makes can be a clear indication of the problem at hand. Whether one of the pipes has been damaged or you're experiencing a broken gasket of some kind, if there is a leak in the line that is small enough the air will hiss out the same as it would from any other pressurized air system. There should also be some performance issues that happened around the same time, so if you're hearing a fairly loud hissing sound that's new coming from your engine there's a good chance that it's a problem with the vacuum.
Poor Fuel Efficiency
Because the vacuum system is responsible for transporting the air from outside of your car through the intake and then ultimately into your engine, if there is a leak somewhere in the system as we said you're going to be experiencing an inconsistent air-fuel ratio in the combustion chamber. Whether that's a lean mixture that has too much fuel and not enough air or the opposite because too much air is leaking into not getting in, you're not going to be burning fuel the way you're supposed to. Either one of these can result in you having to go to the gas station to fuel up far more than you're used to with a poorer performance overall happening at the same time.
Loss of Power
Because the air and fuel ratio is no longer consistent you won't be experiencing the same powerful combustion reaction that you are used to. When this occurs you could end up getting a much weaker combustion reaction or even engine misfires as a result. That's going to slow down your vehicle overall and your engine will seem to be struggling to perform while not being able to produce the power that you're used to.
Poor Engine Performance
If you're experiencing a vacuum leak in your engine there are a number of ways that your engine will likely underperform or react that can be inconvenient or dangerous for the operation of your vehicle. You may experience rough idling, hesitation, and stalling out as well. This is in addition to the engine misfires. If your intake leak is bad enough, this would have to be a fairly sizable hole in the system, then you may not be able to draw on enough air to get your engine started at all.
Failed Emissions
If you're burning a lean air to fuel ratio because of the leak in the vacuum, then your engine will likely be burning hotter than normal. This can increase the production of nitrogen oxide and sulphur oxide which are dangerous chemicals that are produced when the combustion reaction is too hot. Normally your vehicle is able to filter out some of this but when your fuel mixture is burning too hot to consistently that will not be possible and as a result you could end up failing an emissions test.
Check Engine Light
This is arguably one of the least helpful symptoms to notice, but at least it's able to let you know something is wrong. A check engine light can come on for literally hundreds of different reasons so you can't be sure that it has anything to do with a vacuum leak unless you get it properly diagnosed.
That said, the check engine light is helpful to let you know that there is something wrong even if it can't tell you exactly what. When this happens, you can either go to a mechanic to get a diagnostic run on your car or you could pick up your own on board diagnostic scanner tool, or OBD2 scanner, from a site like amazon.com. You can get some of these for as low as $30 to $40. When you plug in the OBD2 scanner after a check engine light comes up on your dashboard it will give you a diagnostic code and direct you to the exact nature of the problem you're experiencing. It doesn't fix the problem in any way, but it does let you know where to look in that can help getting the job done faster and more efficiently.
Can You Drive with a Vacuum Leak?
It's possible to drive for a while with a vacuum leak in your engine but, as we've noted, there are a number of symptoms that you're going to be experiencing depending on the severity of the problem. And while it is possible to drive like this, it's not a good idea to do so.
If you drive with a vacuum leak for a long enough period of time the elevated temperatures in your engine are going to start causing some serious damage. Like we said, the lean fuel mixture is going to burn hot. This will likely be more than your engine cooling system is able to handle so aside from the dangerous emissions that are going to come from your exhaust as a result you can potentially also cause damage to the pistons and bearings in your engine as well.
Your catalytic converter will not be able to handle the high temperature in the exhaust and that could potentially be damaged as well further complicated issues with your emissions.
The potential loss of power that's also associated with driving under these conditions could be dangerous if you are unable to maintain the power and speed that you're used to while you're driving down the highway for instance. For all of these reasons it's definitely dangerous to try to drive for an extended period of time with a vacuum leak in your vehicle. The situation is only going to get worse and the damage will become exacerbated over time if you don't deal with it properly. What could be a fairly low repair bill can end up turning into a massive repair bill if the damage to your engine is the end result. When an engine overheats badly enough, you’re suffering damage to the valves and the pistons that could lead to repair bills that range anywhere from $2,000 to $4,000.
Can I Repair a Vacuum Leak Myself?
While any repair can technically be done at home, a vacuum leak is a potentially difficult one to handle as a DIY repair. The problem with repairing a vacuum leak yourself is accurately identifying where it is in the entire system that the leak is coming from. As we've seen, there are a number of different components in your engine that could lead to a leak. Each one will have to be inspected to figure out where the leak is coming from and if you are not skilled at automobile diagnostics then this could certainly be a problem for you to handle.
An OBD2 scanner may be able to narrow down the source of the problem for you, but there's no guarantee that it will direct you to the exact location. For that reason, it's probably in your best interest to take this one to a mechanic to get it diagnosed and repaired.
If you are going to try to handle this job yourself there are actually a few crafty ways to pull this off to narrow down your focus and figure out what to do more easily. There are videos that can show you some shortcut methods to figuring out how to find the leak and then repair it. For instance, one method of discovering a vacuum leak involves using smoke from a cigar. If that doesn't sound like precision auto repair it’s because it's not, but sometimes you need to improvise to get the job done.
Once you have narrowed down precisely where the leak is, repairing it is a bit of an easier job and you can likely find some guides online to direct you to the specific component that has the problem.
The Bottom Line
A vacuum leak is one of the trickiest problems to deal with under the hood of your car because it's not a specific component, it's an entire system that could have gone wrong. Diagnosis is, as we've seen, problematic, and equally frustrating is the fact that you can still drive your car for a fairly long time with a vacuum leak as long as it's not severe enough. This will encourage some drivers to ignore the problem perhaps longer than they should because it doesn't seem like it's a bad enough problem to merit doing anything about.
As we've shown, you don't want to ignore a vacuum leak for too long because it's not just the fuel efficiency and overall performance that you're sacrificing by letting this go, it's the potential for some catastrophic engine failure that may occur in the future if you do not get a vacuum leak problem addressed as soon as you can. If you've noticed a few of the symptoms we've mentioned in your car, it's best to head to a mechanic to get it dealt with as soon as you can before it spirals out of control and ends up costing you many thousands of dollars to fix.