Signs of a Worn-Out Car Vacuum Pump

What Is the Vacuum Pump?

The vacuum pump is a device that generates vacuum, which can be defined as a removal of atmospheric pressure from a closed space. Since nature abhors a vacuum, atmosphere provides pressure to fill that vacuum whenever it can. Airplanes fly for this very reason, because atmospheric pressure below the airplane wing is higher than the pressure above the wing due to airflow dynamics and the shape of the wing as it cuts through the air.

Vacuum pumps were most typically used first on diesel engines with power brakes and for moving climate control doors in the dash and other such tasks because diesels don’t create vacuum. Some late ‘80s Crown Victorias with emission control air injection pumps included a small vacuum producing aspirator as a part of that pump to assist with vacuum cruise control, which tends to lose its vacuum “muscle” on long hills. Due to the need for vacuum when the engine’s manifold vacuum isn’t sufficient, vacuum reservoirs (those funny looking cans and rounded plastic tanks with one-way valves to store vacuum) were very common for decades.

Turbocharging and variable valve timing both tend to reduce intake manifold vacuum, and both have become very common on vehicles in this century. Many jobs that were once handled by vacuum are now done electronically, with electrically driven servos using motors and gears.

For tasks that require vacuum, vacuum pumps are becoming more common.

The moment you fire up your vehicle, its vacuum pumps start running and don’t stop until you switch off the engine. The pumps work with the intake manifold to ensure that various parts and systems get the pressure they need in order to run smoothly.

However, their constant state of operation wears vacuum pumps out faster than other engine parts. Aside from wear and tear, some of the pump components can also develop other issues.

Bad Vacuum Pump Symptoms

A worn-out vacuum pump can cause issues due to a reduced vacuum supply. Watch out for the following symptoms:

Hissing Noises From Vacuum Leaks

Air leaking out of a faulty vacuum pump is bad news for your vehicle. A vacuum leak alters the pressure difference, which affects the amount of vacuum produced by the pump. Fortunately, you can tell there’s a problem if you catch the hissing sound made by the air escaping from the leak.

A bad vacuum pump isn’t the only possible cause for a vacuum leak. If the hoses that connect the vacuum pump and other parts break or develop issues with their connections, they can also make similar noises.

Brake Pedal Feels Rough or Resists Movement

Do you drive a diesel vehicle with a brake booster vacuum pump? You can tell by the feel of the brake pedal if the pump has a problem.

Normally, the brake pedal feels solid and responds well to foot pressure. When the pump doesn’t produce enough vacuum or stops working, the pedal will become rougher and harder to push down.

Oil Leaks on the Engine’s Left or Right Side

Another common symptom of a deteriorating or nonfunctional vacuum pump is an oil leak on either side of the vehicle’s engine. In many diesel vehicles, the pump can be found on the same side as the brake master cylinder.

The vacuum pump has moving parts that produce heat while they’re running. It needs lubricating oil to reduce friction between the parts that come into contact with each other. The lubricant also cools the pump by absorbing and expelling heat, allowing the device to keep running safely.

A damaged or worn-out vacuum pump can develop a leak. If it runs short of lubricant, it can get dangerously hot, which will affect its performance and shorten its service life.

Check the ground under the engine for signs of an oil leak. If the vacuum pump is the source of the dripping fluid, it might have failed and you’ll need to replace it.

Malfunctioning Air Conditioning

A failing vacuum pump can also cause your vehicle’s air conditioning (A/C) to malfunction. In diesel vehicles, the A/C uses vacuum to move externally drawn air through the cooling system and into the cabin. If the pump fails to produce enough pressure difference, the A/C might have problems producing air from its vents.

If your A/C has been recently fixed but suddenly stops working, check your diesel vehicle’s vacuum pump.

More About the Vacuum Pump

Vacuum pumps can be divided into two types: Mechanical pumps and electric pumps. Most older vehicles have mechanical pumps that get their power from the camshaft. An increasing number of new vehicles use electric pumps that take orders from the powertrain control module (PCM).

The location of the vacuum pump can vary depending on various factors like your vehicle’s engine. You can find it on top of the cylinder head or mounted near the brake master cylinder.

Normally, the intake manifold produces the vacuum needed by the vehicle. But there are vehicles that require more vacuum than the manifold can create, such as vehicles with direct injection engines and turbo engines with variable valve timing.

For more technical information on vacuum pumps in cars, read our advanced discussion on engine intake vacuum.

What Does a Vacuum Pump Do in a Car?

The exact job of the vacuum pump depends on the internal combustion engine that powers your vehicle. In a gasoline vehicle that burns unleaded fuel, the pump releases pressure in the crankcase that drives various belts and pulleys for parts ranging from A/C to the alternator. In diesel vehicles, the vacuum pump powers the A/C, brake booster, and other systems.

How Much Does a Replacement Vacuum Pump Cost?

A replacement vacuum pump can cost anywhere between $35 and $310. The price can vary based on the pump’s brand and your vehicle’s year, make, and model.

An In-Depth Look at Engine Intake Vacuum

On a traditional naturally aspirated engine, vacuum is created in the intake manifold because the throttle plate restricts airflow as the engine “breathes.” With every intake stroke of every piston, air is drawn from the intake manifold. A diesel engine, due to the lack of a throttle plate, doesn’t produce vacuum in the intake manifold. Some diesels do have an electronically driven throttle plate used during exhaust gas recirculation (EGR) to create a pressure differential for the purpose of assisting EGR flow into the intake.

On a traditional naturally aspirated engine, vacuum is created in the intake manifold because the throttle plate restricts airflow as the engine “breathes.” With every intake stroke of every piston, air is drawn from the intake manifold.

– Richard McCuistian, ASE Certified Master Automobile Technician

A naturally aspirated gasoline engine at wide open throttle produces very little vacuum. The pressure in the intake is very near atmospheric pressure. A turbocharged or supercharged engine, during boost events, will actually have pressure in the intake manifold that is greater than atmospheric pressure.

A Quick History of Intake Vacuum

Early gasoline powered engines didn’t use intake vacuum for anything, but in the early 1920s, Pierce-Arrow added a vacuum assist device to their hydraulic brake system. Power brakes eventually became the order of things. If the vehicle is equipped with a diesel engine or if the engine compartment is too crowded for a vacuum brake booster, a hydraulic assist system will be used for power brakes.

In a vacuum operated servo, a flexible diaphragm or small moveable piston will receive Intake manifold vacuum by way of a switching device so that the reduced pressure and the opposing atmospheric pressure are used against each other for the purpose of doing work. It’s a simple principle: lower the pressure on one side of a diaphragm and the atmosphere will apply pressure on the opposite side. A rod connected to the center of the diaphragm will use this movement in a mechanical fashion.

The most common early use of intake manifold vacuum was to move the breaker plate in the engine’s ignition distributor to advance ignition timing as the throttle is opened. Vacuum is delivered to the distributor advance diaphragm (and other diaphragms) via rubber hoses.

In the early 1960s, the PCV valve became the first emission control device, applying vacuum to the crankcase to purge blowby from the piston rings rather than simply allowing crankcase gasses to pollute the atmosphere. As emission controls became more pervasive, vacuum servos took a very large role (such as in the early ‘70s with the advent of EGR). Cruise control systems tended to use vacuum diaphragms to regulate the throttle opening to maintain set speed, and some carburetors used vacuum operated idle load compensators to maintain idle stability during changes in engine load at idle (power steering, A/C clutch activation, etc.)