Installing Oxygen Sensors

A number of hot rod and street rod builders are beginning to use engines with modern electronic fuel injection (EFI), largely because it offers improved drivability and requires less maintenance than a carburetor. The only downside is that EFI requires installing an oxygen sensor in the exhaust system. It's a fairly simple procedure, though, as shown here.


The oxygen sensor (also known as an O2 sensor, lambda sensor, or EGO sensor) is one of the most critical sensors on a fuel-injected engine. It resembles a spark plug and is located in the exhaust manifold, upstream from the catalytic converter.


When at operating temperature, the sensor becomes a miniature battery, which generates a voltage based on the differential between the oxygen content of the exhaust gas and the oxygen content of the ambient air. By this method it measures the amount of oxygen in the exhaust stream, allowing the Electronic Control Module (ECM) to compensate to some degree for various fuel grades, engine wear, altitude changes, usage of oxygenated fuel, and whether the fuel mixture is too rich or too lean. Another big benefit is the ability to keep emissions as low as possible.


When a modern engine is transplanted into an older project car it normally has a wiring harness and the oxygen sensors. Older oxygen sensors are one-wire units, but they don't last as long the newer three-wire units. Most cars made after about 1990 have the three-wire system.


What's the difference between the single and multi-wire units— Because the O2 sensor must be pre-heated to function, many newer units contain a little 12-volt heater that brings it up to temperature sooner, offering better fuel economy and drivability earlier. The number of wires coming out of the unit can identify these sensors.