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A vacuum leak may not seem like a big deal. After all, a leaking vacuum means that air is leaking into rather than out of the vehicle engine.

Well what the heck is wrong with that? Surely it would be more of a big deal if air was leaking out, right?

Wrong!

A vacuum leak is actually a pretty big deal, with a number of negative implications for your vehicle. That’s why in this article we’re going to take a good look at this irritating but simple mechanical issue.

car vacuum

We’ll look at what it is, how to detect it and, most importantly, how to repair it! But first, given what we’ve said above, we better start by looking at:

What is a Vacuum Leak?

What it an engine? Or rather, to phrase that question correctly, what is an internal combustion engine, the proper name for a car engine?

Well the clue is the second word of the name, combustion.

An engine is just a box to contain a series of controlled explosions. This occurs when combustible material (there’s that word again) is mixed with air and, well, it combusts.

This air enters the car engine via a butterfly valve connected to the throttle. The more the throttle opens, the more air is allowed to enter which in turn leads to more combustion with greater power.

Just picture Vin Diesel standing on the gas pedal in Fast and Furious 56: Prius Uprising. He is opening the throttle there and letting air into the engine.

However, as air enters the engine it creates a vacuum in the air intake manifold.

What is a Vacuum Leak a Big Deal?

Vacuums are powerful things. Why do you think your dog goes crazy every time you switch a vacuum cleaner on, huh? He knows the power of the vacuum that’s why.

Do you know who else know the power of a vacuum?

Car makers!

They use the vacuum created in the air intake manifold to power or at least assist in a range of secondary functions within the car.

The brake system, for example, makes use of the vacuum to reduce the amount of power you need to send through the brake hydraulic system. That means that it’s easier for you to operate the brakes – you don’t need to risk rupturing your Achilles every time you need to slow the car down quickly.

The vacuum also plays a part in helping your vehicle meet clean air quality criteria and laws. Vacuum is used to operate the EVAP system for example, capturing unburnt fuel vapor when the engine is switched off. This vapor is held in charcoal canisters then recycled back through the engine next time it is turned on.

So when the vehicle engine is leaking vacuum, it can have a big impact on:

  • Engine Performance

By affecting the carefully calculated air and fuel mix the engine needs to operate efficiently.

  • Secondary Systems

Like the brakes. Which are an important part of the vehicle.

  • Air Quality

Via the EVAP system. This can lead to dirty exhaust gases (which can get you fined or worse) plus build ups of deposits of fuel and carbon later in the exhaust system.

So that covers what an engine vacuum leak is and why you need to fix it – the next thing we need to know is what signs the car will give you that there is an issue with the vacuum system.

You should be keeping an eye out for:

Symptoms

  • Fast Idle

This symptom is more likely to affect older cars without a computer controlled idle system. But if you are waiting at a stop sign in an older vehicle, and the engine is going crazy without the clutch engaged or in neutral, that is a classic sign of an engine with a vacuum leak.

  • Check Engine Light

The absolute opposite of the symptom above as you are only going to find this symptom coming up on modern cars, not on Herby the Lovebug. We have covered this on previous articles, but as any car owner will testify the Check Engine Light is a pretty blunt weapon. If the light activates in conjunction with any of the other symptoms here, then you can add vacuum leak to the suspects list before you get your diagnostics done.

You will experience this mostly during hard acceleration, such as up an incline or hill, when pulling away quickly from stop signs or red lights, or when trying to outrun the cops after your bank heist goes wrong. In these instances when you are taxing the engine and asking for more power, whatever affects the vacuum leak has on the air and gas mixture will be made many times worse. This will translate into a misfiring engine during acceleration.

  • Stalling

This symptom is also connected to the one above. Because the vacuum leak is affecting the air and gas mixture inside the engine, it is more likely to stall. This is actually a sign of a serious leak, as the vacuum is affecting the fuel mix to such an extent the engine is literally struggling to keep running.

  • Vibrations

Finally if notice your car is shaking like a pig in an abattoir that can be a symptom of a vacuum leak. The shake can get worse as power is applied through the engine too. This alone is a strong symptom of a vacuum leak, but if it is also happening with frequent stalling, that means the finger is even more firmly pointed at a vacuum leak as the cause.

car engine

How to Find a Vacuum Leak

So yeah, hopefully we’ve done a good job here of highlighting that a vacuum leak is pretty bad news for you and your car. If you’re on board with this, then you probably want to know how you can find a vacuum leak.

Luckily there are several options open to you, many of which are of a McGuyver level of make do and mend mindset. You can, for example, use:

  • Smoke

Or Automotive smoke to give it the correct name. It normally comes in a can that you hang near the air intake manifolds. Once activated it puffs out smoke which is sucked through the system. A leak in any of the vacuum hoses will see this smoke leak out. Simple, but effective. This is the method that pros will use in a garage to detect vacuum leaks, often with sensors attached to key intakes to monitor the smoke.

  • Soapy Water

Yep that’s right, throw bubble mixture at the problem – which is actually not a bad philosophy for life in general. This method is actually twice as awesome, as not only will it detect a leak, it will show you exactly where it is too. This is what you do here. Fill a spray gun with dish soap and water. Turn the engine on and leave it idling. Spray the soapy water near to the suspected leak on the vacuum hose or connectors. If the idle becomes more stable when the hose is covered in soapy water, this is because the thicker liquid is plugging the vacuum leak a little, improving the air/gas mixture inside the engine.

  • Diagnostics

Of course these days on a modern car, it will probably just be a case of plugging into a diagnostic device. Still, it’s useful to know the old ways, and of course how to detect a vacuum leak on an older car. If you bought Fred Flintstone’s old car for example.

How to Repair a Vacuum Leak

Luckily, repairing a vacuum leak is – or at least can – be a pretty straightforward repair. Most of the time, a vacuum leak will be caused by one (or if you are very unlucky several) of the vacuum hoses themselves.

These very simple little components are made of rubber, usually synthetic rubber. Because of this, over time they will become brittle as the elasticity of the rubber material is worn out. They will get dry, they will start to crack and – eventually – they will start to leak vacuum.

In the short term, say before you have purchased new hoses, you can affect a repair by wrapping tape, like Gorilla tape, around the offending hose. This will help to make a better seal and keep a little more of the vacuum in the hose where it belongs.

Be aware as well that since all the hoses were probably installed at the same time, you may notice them failing together or in quick succession. So it makes sense to buy several vacuum hoses at the same time and replace them all in one go.

If you replace the hoses and still don’t see any improvement, then the problem could lie with the air intake manifold, carburetor or even the throttle. All of these are far more complex repairs, way more than what we can cover in this article!

We would suggest repacking the rubber vacuum hoses first as this is a relatively cheap and straightforward repair. If this fails, then investigate further, perhaps with the help of a professional.

fixing engine vacuum

Conclusion

That’s it folks! A vacuum leak is relatively easy to find, especially on modern vehicles. In terms of repairs, it can often be very straightforward one that mot people can perform themselves. It can though sometimes be a more complex repair, often needing high tech equipment and professional know-how.

Either way, if you notice one or more of the symptoms we talked about above it is a very good idea to investigate and repair if you can.

Sources:

  1. Vacuum Hose Replacement Service – YourMechanic
  2. Is it Safe to Drive With a Vacuum Leak? – YourMechanic

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