Air Pump - What It Does and How To Diagnose

Article by Mark Trotta

Starting in the 1960s, there was concern over the significant amount of unburned and partially burned fuel in automotive exhaust. In an effort to decrease this source of emissions, the air injection system was created.

automotive AIR pump

A common A.I.R. (air injection reactor) system would include the Air pump, a fuel-mixture control-valve or air diverter valve. Also in the system are air injection tubes and check valves.

The A.I.R. pump is generally a sealed bearing unit that mounts to the front of an engine. Although some were electrically operated, most were powered by an engine-driven belt along with other accessories, such as alternator, power steering pump, and air-conditioning compressor.

What Does An Air Pump Do?

A.I.R. pumps, commonly referred to as air pumps or smog pumps, help reduce emissions in two ways. While your car's engine is cold, it pumps excessive hydrocarbons back into the engine for re-combustion, providing a more complete combustion. It also diverts air to either the atmosphere or downstream to the oxygen sensor.

How An Air Pump Works

Engine exhaust (which contains unburned hydrocarbons and carbon monoxide) is routed into the AIR pump, then compressed and injected into the exhaust port of the cylinders. The gases then combine with unburned hydrocarbons and carbon monoxides at higher temperatures, causing a chemical reaction. Now the spent exhaust is less harmful to our environment.

Also contributing to lower emissions were recalibrated carburetors and distributor settings, and also higher engine-operating temperatures. Together, combustion efficiency was improved and harmful emissions were reduced.

Symptoms of a Bad Air Pump

A bad Air pump may reduce engine power, give poor acceleration, or cause stalling, rough-running, hesitation, or rough idle. Of course, these symptoms are the same as many other engine problems (carburetor, tune-up, etc.) And if your 'Check Engine Light' illuminates, your vehicle will fail it's emission inspection. So how can you check?

A diagnostic check with a Code Scanner can pinpoint the general cause of the problem. But before you do that, check for a leaking or clogged hose (or a missing belt).

Can I Remove My Air Pump?

Classic cars are worth more in factory-stock condition, which means having the correct emissions equipment installed and operative. There have been stories of people removing the guts of the pump and re-installing it back on the car, to keep the "factory" look. Today, we know that a correctly working smog pump robs very little power from the engine.

Missing Air Pump

Many cars from the late sixties and seventies have had their smog equipment removed. If your old car is missing the air pump, it's probably also missing the manifold tubes, check valves, diverter valve, mounting bolts and brackets, as well as hoses and clamps. These can be hard to find, but often these can be taken from a similar year and model donor car.

automotive AIR pump

Needed or Not

The original Fiat Spider, produced from 1966 to 1985, featured an efficient twin-cam four-cylinder motor. These engines were well-designed, and ran cleanly and efficiently. But starting in 1974, all cars bound for North America were required to have pollution devices - regardless of whether they were really needed.

1979 Fiat Spider emissions

In order to continue selling to its largest market, Fiat, like many other manufacturers, complied by adding on smog equipment, which burdened motors, choked performance, and caused driveability issues. Air pumps were added, along with restrictive manifolds, tiny carburetors, scores of vacuum lines, and other emission controls. Performance and sales both suffered.

Eventually, car manufacturers designed and produced more efficient fuel-injected engines, which started appearing in the early eighties. Computer controls were developed to help regulate engines, and the amount of unburned fuel into the exhaust was greatly reduced. Soon after, the need for an air pump faded.


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