How to Find and Fix Vacuum Leak


Easy step by step guide on how to detect and fix an automotive engine vacuum leak, this information pertains to most vehicles.

How to fix vacuum leak

In the vehicle, the vacuum pump is one of the most vital systems. As its name implies, its main role is to provide a vacuum, which helps in operating other car components such as secondary air valves, brake boosters, central locking systems and turbocharger controls, among others. Looking at this system’s significance, you need to know how to fix vacuum leak in your car maintenance practice.

A vacuum leak is a common occurrence that will affect the performance of a vehicle. The earlier you detect it, the better as you can develop a solution that will prevent the issue from escalating.

This article will have an in-depth look at vacuum leaks and what to do if you have such a situation on your hands.

What is a vacuum leak?

A vacuum leak is a situation where there is a leakage in the engine’s vacuum system. The leak occurs anywhere between the engine and the mass airflow sensor and can bring about some imbalance.

In the case of a leak in the system, there are telltale signs that will point out the issue. If the vehicle in question is a new-age model, then the sensors can point it out. Fuel-injected vehicles have the mass airflow sensor installed at the air filter box, and it measures the airflow into the engine.

In case there is a leak in the system, the airflow will be disproportionate, leading to an unequally disproportional air-fuel mixture ratio. The ration might be higher than 14.7:1, and in mechanical circles, it is referred to as a lean mixture. Here, there is too much air mixing with the fuel.

Too much air may lead to a slower engine, or in severe cases, the engine won’t move at all. The massive airflow to the engine usually leads to miscalculations from the engine’s computer, leading to low fuel injection compared to the airflow.

There are several symptoms of a vacuum leak, as we will see later on in the article.

What are the symptoms of a vacuum leak?

Poor fuel efficiency
Fuel injector vacuum leak symptoms will present themselves in the form of poor fuel efficiency. As earlier hinted, there will be excessive air intake from leading to a disproportional air-fuel mixture. It will, most of the time, be in a ratio above 14.7:1, which is a higher limit for this mixture.

The result is there will be poor fuel use in the car, and its consumption may increase abruptly. If you notice such in a car brought to your mechanical practice, you may want to check on the vacuum system to see if there is a leak.
At times, you may notice a hissing sound when the vehicle is moving. It is a pointer that the vacuum hoses are broken, or they are faulty.

The fuel efficiency issues come by due to a delay in exhaust gases leaving the combustion chamber. The buildup of exhaust gases will lead to poor burning of the car fuels. You may also notice white smoke, which is indicative of a faulty injector system.

Leaking oil

Another sign of a vacuum leak is oil leakage. Vacuum pumps can be located either on the car’s left or right side, which is close to the master cylinder of diesel-operated vehicles. The pumps need lubrication for their efficient operation and also to maintain a stable internal temperature.

As such, if you notice an oil leak from the car on the left or right side, there is a chance that it may be from the vacuum pump. Check on the pump to rule out this issue before things get severe.
Check engine light turns on When the check engine light turns on, it is usually a cause for alarm for many as they ponder the problem. In the event of a vacuum pump leak, the mass airflow sensor and the fuel injector might malfunction due to the excess airflow.

As a mechanic, you need to check out these components to ascertain the issue, especially if more signs point to a faulty vacuum system.

The brake pedal is hard to press

Heavy diesel engines rely on the vacuum pump booster to improve the brake efficiency and overall performance. The vacuum from the pump helps bring the right suction for you to engage the brakes. These brakes feel hard to press, but they move perfectly when you apply some little force.

The contrary is true when the vacuum pump fails; hence, it cannot produce enough suction for the braking system. As such, when you press on the brake pedal, it feels hard and rough.
When you notice such an issue on a vehicle, try and inspect it immediately to check if the vacuum pump is in proper shape.

Black smoke

You may also notice black smoke from the exhaust. The black smoke shows poor combustion due to poor fuel efficiency and improper air to fuel mixture.

Engine problems

You may also notice problems with your engine, indicating that all is not good with the vacuum pump. The engine might stall, especially when idle. In this case, the problem might be the air to fuel mixture, which is not proportional, or the buildup of exhaust gases.

There can also be accelerator problems, or an abnormal idling speed, which is faster than it should be. Also, pay attention to the typical vacuum leak sound, which most of the times comes as a hiss. If the hissing sounds become lengthier and more pronounced, you should check the vacuum system.

A rough idle and stalling are other engine issues that may point to a vacuum problem. Also, be on the lookout for the engine blow-by.

  • These are some of the causes of a vacuum leak in the vehicle.
  • An improperly installed intake snorkel.
  • Intake manifold vacuum leak can come by due to shrinking gaskets and O rings that seal the intake manifolds gaps.
  • Cracked or ripped plastic and rubber hoses of the vacuum system. They get damaged mostly due to prolonged use and aging.
  • Damaged plastic and rubber parts of the Positive Crankcase Ventilation system.
  • The EGR sticking open due to carbon buildup.
  • Damaged brake booster.

How to find a vacuum leak

Once you ascertain that you a vacuum leak issue in a vehicle, you need to repair it immediately. Here comes the hard part, locating the vacuum leak. You can use the following methods to help you locate the leak and make the necessary repairs.

General inspection

The first step in finding a vacuum leak is through general visual inspection. Here, you look for burst hoses and worn-out plastic or rubber connections. This is a simple process, especially if you have experience dealing with engine parts.

As a mechanic with a keen eye, you can spot anomalies that point to a vacuum leak on the entire vacuum system. The hose system is unique for every car model, and you will need to pay attention to the clamps that hold them together.
You can try moving the hoses, primarily at the clasps sideways, to check if they are broken.

Check for vacuum leaks using soapy water

If you are a pro in the auto-repair scene, you must know how to check for vacuum leaks with soapy water. To pull this, you need a spray bottle filled with soapy water. It is the easiest and most affordable way to check for the anomalies after performing the hoses’ general inspection and their connections.
You should spray the soapy water around the inlet and the hoses as the engine runs. You will notice bubbles popping out of the affected areas, meaning there is air leakage.

Using a smoke machine

You can also check for vacuum leaks using an automotive smoke machine. It is a simple and professional way of checking for leaks in the engine system, promising you accurate results. Using this method, you remove the cover of the top of the intake manifold and then remove the intake tube from the throttle body.

You can seal the inlet with a rubber duct or plastic wrapping and connect the smoke machine’s nozzle to a place like a brake booster. Now you press the smoke button and wait for a few minutes for the smoke to concentrate the inlet.
You can take note of areas in the system where the smoke comes out in large amounts, which indicate a leak in the system. You can also check the dashboard to see if the check engine light comes on, as it will help you check on other problems in the system.

How to check for vacuum leaks with WD40

In your mechanic practice, one of the companions you should always have with you is a can of WD40, a multipurpose carb cleaner. You can use this cleaner in various areas, such as checking for vacuum leaks on a vehicle.
The good thing with WD40 is that it won’t leave the surface dirty or damage the plastic components. On how to check for vacuum leaks with WD40, you start your engine and leave it idle. You then spray the cleaner on the hoses and around the inlet.

If your engine’s speed decreases when you spray a particular region, it indicates that it leaks. When using this method, having a keen eye is recommended, lest you miss detecting the affected areas.

Generally, when checking for leaks, you should pay attention to contaminations inside the hoses, such as carbon and dirt buildup. Additionally, ensure that the hoses are not lying on hot surfaces, which might be the major cause of the leaks.

How to fix vacuum leak

Once you detect a vacuum leak, you need to fix it before it becomes severe and hard to sort. An apparent leak can affect the vehicle’s performance and, if not dealt with immediately, can lead to secondary problems in the engine system, mainly in the injection system due to the improper air-fuel balance.
Below are steps to follow to help fix a vacuum leak.

Seal the holes

If the issue lies on the hoses, you can make a steady repair by bringing a sealant to shut the holes. Rubber sealants can do the job perfectly, the same as gorilla duct tape. You need to map out the affected areas during the general inspection, not to miss any area.

When using a sealant, ensure that the hoses are not near any hot surfaces as they can melt the sealant or cause further damage to the relay unit.

Replace the hoses

In case of extensive damage to the hoses, replacement is the only solution. If you make repairs to it, the issues may recur and be harder to deal with. While repairs might seem affordable in this instance, the case’s lengthy presentation may make it harder to deal with in the long run.

Look for a credible spares dealer and get the right item befitting the vehicle under your watch. It is advisable to repair all the hoses at once, as they were installed simultaneously; hence, the wearing process may be at the same rate.

Check on the entire vacuum system

At times, the issue at hand may be the intake manifold vacuum leak. Here, you will not notice any problem with the hoses because the issue is at the main system. While it may be a complex area to deal with, some auto-repair skills can guide you to have the part in working condition.

Check the intake manifold and see if there is any damage. A smoke machine can help you in this instance. If the problem lies at this system, then you may need to replace it as a sure way of saying goodbye to recurring vacuum leak issues.

Frequently asked questions- FAQs

Is a vacuum leak expensive to fix?

In most cases, it is not that expensive to fix a vacuum leak, especially if you detect the issue earlier. In this scene, a sealant such as glue or gorilla duct tape can do the job correctly. However, the cost may go up if you have to repair the hoses or the intake manifold.

Though, when you look at the cost of not repairing the vacuum leak in time, you get the picture that fixing it in time will save you a lot of funds and prevent other secondary issues such as a stalling engine.

Can you drive with a vacuum leak?

You can drive with a vacuum leak; however, it is not advisable as you may cause further damage to the vehicle. When driving with a leak, you will notice issues, such as a hard-to-press brake pedal, car stalling, the check engine light turns on, smoky exhausts, and many more.

Driving is possible, but you will put your life and other road users in danger, primarily when the brake fails to initiate. In the long run, the vehicle will be unroadworthy and won’t be able to move.

Can a vacuum leak ruin your engine?

Yes, the leak can ruin your engine, especially the injection system, due to the improper air-fuel mixture. The lean combination of the two can lead to a buildup of exhaust gases, leading to poor fuel economy.

The leaks can also cause a miscalculation from the engine’s computer. That is why you have to deal with the issue as soon as you notice it to prevent the engine’s damage.

Will a vacuum leak throw a code?

A leak results in the check engine turning on, and it will store trouble codes. The trouble codes will show due to the disproportional mixture of air and water or malfunctions in the injection system. Misfiring can also lead to a code from the engine control unit.

Can a vacuum leak cause transmission problems?

One of the areas a vacuum leak will affect is the transmission system. The vacuum is responsible for a sizeable portion of the vehicle’s transmission power, and if there is a leak, the power levels depreciate.

You can notice the transmission issue when shifting, where there is some imprecision in the shifting points.

How do you check for smoke in a vacuum leak?

Checking for smoke in a vacuum leak is essential when you want to know which areas have a problem. You bring in a smoke machine and connect it to the intake manifold and wrap up the inlet using plastic wrapping.

When you connect the smoke machine, you can easily tell where the issue is in the vacuum system.

Final thought

In a vehicle, the vacuum pump is an essential component that helps run other systems such as transmission and braking. The pump can have issues such as a leak, which may affect the vehicle’s performance in several ways.
Some of the signs of a leak include stalling, poor fuel economy, and transmission issues. This article is a mechanic’s guide to understand, detect and sort out the vacuum leak issue. Also, be on the lookout for such problems so that you deal with them earlier before they escalate and ruin your engine.

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