From minor issues to major issues, there are many mechanical issues in vehicles, but the tricky vacuum leak is one of the most puzzling issues of all. The symptoms associated with varying levels of severity are all hidden scavengers that affect drivability.
Confirming the issue and locating the culprit are essential before any repairs can take place. We review the overt (and subtle) symptoms of vacuum leaks and their likely origins.
What Is a Vacuum Leak?
A vacuum leak can be described quite simply as an uncontrollable source of unmetered air being introduced into the engine’s intake by way of compromised hoses, gaskets, or components.
The introduction of unmetered air poses a serious risk of disrupting an engine’s desired air-to-fuel ratio, which will ultimately affect the combustion being delivered.
That said, to truly appreciate the issues presented by a vacuum leak, one has to have a working understanding of the principle of engine vacuum first.
Vacuum (or negative pressure) is created inside an engine as a piston descends after combustion occurs, during the intake stroke. This creates a suction-type effect, drawing in air into the respective cylinders through their intake valves.
The total amount of air drawn in is metered by the throttle body of an engine. This component houses a butterfly that opens and closes depending on the demands of the system to allow or restrict air available for combustion.
It should be noted that the metering, which is performed, can be “thrown off” when there is some kind of leak in the intake system, downstream from the throttle body, which allows unmetered air to enter the intake tract.
Any disruption in the predetermined air-to-fuel ratio will create several driving-related symptoms.
Function of Vacuum Hoses in A Car
Vacuum hoses serve to transport vacuum pressure from the engine to several different parts of the automobile, including brakes, transmission, and the HVAC system.
The vacuum pressure that is transported is used to exert on various components of the car, such as brakes and transmission.
For example, your vehicle’s brake system uses the vacuum pressure to multiply the applied force as you push down the brake pedal, making it easier to stop the car.
The transmission that also employs vacuum pressure in a multitude of ways to facilitate gear transitions while having the documentation to document that the operation of the vehicle transmits smoothly and efficiently as possible.
Furthermore, the vacuum hoses help reduce emissions and improve fuel economy when allowing the engine to work under vacuum pressure as well.
Vacuum hoses enable an engine that burns a correct air-fuel mixture, and when the engine works correctly through vacuum agglomeration, as much as possible fuel savings and a reduction in harmful emissions.
What is the sound of a vacuum leak?
In some cases, vacuum leaks can be heard and make the diagnostic process faster. However, major leaks are usually easier to hear than minor leaks.
Vacuum leaks often sound like a light whistling or hissing sound (similar to a shop-vac operated in a small room).
While it is typically impossible to know where the air leak sound is at, many mechanics up their chances by placing their ear in the engine compartment of a vehicle and slowly moving from one side of the engine to the other.
Signs of a Vacuum Leak
A vacuum leak can manifest with a variety of symptoms. Some symptoms can affect drivability, while many are more cosmetic.
However, being able to identify the many symptoms of a vacuum leak can be helpful in trying to fix the situation when you discover the issue. Here is a list of the top symptoms of engine vacuum leaks.
#1. Check Engine Light.
In nearly all cases, there will be a corresponding check engine light when there is a vacuum leak. The check engine light indicated a diagnostic fault code has been set, as a result of one or more identified performance issues
In the case of a vacuum leak, an engine’s PCM/ECM has determined that the engine’s fuel trims have begun to reflect a positive or lean trend. P0171, P0174, and P2279 are common trouble codes related to leaks.
#2. Erratic Idling.
Vacuum leaks can cause an engine to idle erratically, typically higher than normal idle or what looks like a car that’s revving on its own.
Also, a car’s tachometer can fluctuate on idle, either way, up or down, a difference of as much as 300-400 rpm, in a number of seconds.
In most situations, this symptom presents itself when there is a significant vacuum leak.
#3. Hesitation or Stalling.
In severe cases, a vacuum leak can even lead the engine to hesitate or stall brazenly. This happens when carbon monoxide or other foreign gases are introduced to the intake track, and the engine’s preset air-to-fuel ratio is thrown out of whack.
Unfortunately, this symptom is not only hazardous but may also be dangerous, depending on the situation you find yourself in.
#4. Rough Engine Operation.
In addition to unmistakable hesitations and stalling, a large vacuum leak can lead the engine to misfire or backfire.
Again, this happens when unregulated air is intruding on the engine intake manifold, introducing a negative impact on the vehicle’s predetermined air-to-fuel ratio. This almost exclusively occurs in the form of a noticeably lean condition.
#5. Strange Engine Noises.
Vacuum leaks tend to come hand in hand with some odd sounds, squealing, a whistling or a hissing sound. These sounds occur whenever air is pulled through small cracks in the intake gasket or vacuum hoses.
Fortunately, all of these sounds should also prove useful when you are trying to locate the vacuum leak. You can simply listen for the source of the whistling and hissing, and isolate the leak to a specific area of the vehicle’s engine compartment.
#6. Poor Acceleration.
When your vehicle has a vacuum leak, unwanted air can enter the engine through a path not intended for air. This unwanted air upsets the normal air and fuel combination that the engine needs to run efficiently.
As a result, the engine runs too lean, meaning that there is too much air and not enough fuel in the gas mixture at the time of intake. This translates into a whole host of issues, including poor acceleration.
Common Sources of a Vacuum Leak
There are many different sources of a vacuum leak in an engine, and some can be much worse than others.
Knowing these sources can be very helpful when doing repairs. Below are some of the more common sources of vacuum leaks on engines.
#1. Dry-Rotted Vacuum Hoses.
Dry-rotted vacuum hoses are one of the most common sources of vacuum leaks on an engine. At one point in time, there were probably 2-4 hoses connected to your vacuum system, but over time, while sitting in a hot, humid environment, first your hoses became dry-rotted, and then cracked, and then opened.
Oftentimes, tiny hairline cracks will be formed, and it is possible any one of them will admit unmeasured air to an engine.
Repair Cost: $50-$150
#2. Cracked Intake Hose.
Most vehicles will have some type of medium-sized plastic intake hose (or tube) that connects the air filter housing to the throttle body (the device that ultimately sends air to the engine). Intake hoses can become brittle over time due to constant high heat exposure.
Sometimes during a routine maintenance of the air filter element, you will displace the intake tube or hose when removing the air filter element.
The only option is to have a damaged intake hose replaced.
Repair Cost: $75-$200
#3. Defective Intake Manifold Gasket.
As an engine ages, its intake manifold can fail. When this happens, outside air will be drawn from below a vehicle’s hood, into an engine’s intake manifold, without any method of metering.
As a result, a lean condition will occur on one or both of the engine’s banks and can affect a vehicle’s drivability. Unfortunately, gasket replacement is not easy nor inexpensive.
Repair Cost: $200-$600
#4. Cracked Intake Manifold.
In rare cases, an intake manifold can crack, allowing air to be drawn through any open intake valves of an engine. This can happen when an engine overheats, but can also happen with an intake manifold from poor casting methods.
When this happens, the only option is replacement, which is usually costly and time-consuming.
Repair Costs: $300-$750
#5. Stuck EGR Valve.
An EGR valve is an important component of a vehicle’s emissions system. It takes exhaust gases and puts them back into the engine’s intake manifold for more combustion. However, exhaust gas is not put into the engine at all times.
A stuck EGR valve, caused by carbon fouling, will create a vacuum leak to allow exhaust gases that have been misrouted into the intake
Repair Cost: $150-$350
#6. Brake Booster Diaphragm Leak.
Most vehicle brake boosters are connected to the intake manifold of an engine via a vacuum line or lines. A diaphragm and a vacuum make up this assembly, which provides brake assistance when needed.
But any rupture in this diaphragm will lead to a substantial vacuum leak and also may cause a hissing or whooshing sound when the brakes are depressed. With the diaphragm rupture, a vehicle’s power-assisted brakes will be in jeopardy, and this is dangerous.
Repair Cost: $350-$1200
#7. Defective PCV Valve or PCV Hose.
A vehicle’s PCV valve (positive crankcase ventilation) removes excessive combustion gases from an engine’s crankcase and puts those gases back into the engine’s intake to combust.
These PCV valves or hoses do tend to fail with age, causing a substantial vacuum leak, resulting in a replacement.
Repair Cost: $50-$150
Is It Safe To Drive With A Vacuum Leak?
It is always best practice to drive a vehicle with a noticeable vacuum leak, no longer than necessary.
In a “best case” scenario, driving a vehicle with a clear vacuum leak can create many drivability problems, including but not limited to an unstable idle, reduced performance, and stalling; the “worst case” scenario can be more serious.
Operating an engine for an extended period with a significant vacuum leak can cause permanent damage to the engine.
A vacuum leak can create a condition of lean air-to-fuel mixture, ultimately resulting in excess heat in the combustion chamber. In many instances, damage occurs to the engine’s pistons and exhaust valves.
Regardless of the severity of the vacuum leak, locating the cause of a specific vacuum leak should occur as soon as possible. This greatly reduces the likelihood of damaging your engine.
If you are not comfortable with such repairs, you should consider making an appointment with a trusted service center at your earliest opportunity.
Can I Fix A Vacuum Leak Myself?
Yes, you can fix a vacuum leak yourself. But this assumes you can locate the source of the leak itself. This process may be relatively simple in the case of a small vacuum leak; locating the leak is often much more difficult, depending on the size of the vacuum leak.
Once you have identified the source of the vacuum leak, you will be able to develop a strategy for both the diagnosis and repair.
Some vacuum leaks may inherently be easier to repair than others. A vacuum leak can arise from a dry-rotted hose or a failed intake gasket. Repairing a dry-rotted hose usually takes minutes, repairing a failed intake gasket usually takes longer and is much more labour-intensive.