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Copyright - Things That Go - 2016

Things That Go

Fuel injection was introduced as early as the 1950s. Chevrolet used a mechanical version of it in the Corvette. Performance was the only reason at the time. Several manufactures over the next 2 decades also used it in certain models. Volkswagen introduced it in 1968 in their Type 3 cars. It was an electronic system, very simple by today’s standards. By the late ‘70s auto manufacturers were being challenged by both emission regulation and fuel economy. Carburetor engines were loaded with valves and pumps to try to meet emission standards. Again, Volkswagen in 1976 used a mechanical injection system on some models, and in 1977 all models used fuel injection.

Mechanical injection, no computer involved, was very limited to what it could do. Fuel injection by design places a nozzle near the intake port or in the intake manifold which greatly improved emissions even though that was not the primary intention. The first fuel injection systems greatly improved power, fuel economy and drivability . But as emission standards tightened it just wasn’t enough. Electronic fuel injection, using a computer was up to the task.

Electronic fuel injection using a computer and a sensor to monitor the exhaust output and make changes was the breakthrough needed. The oxygen sensor is the key component to controlling emissions. In 1980 the oxygen sensor combined with a computer, the PCM (Powertrain Control Module), or ECM (Electronic Control Module) was the answer, and still is!

An internal combustion gasoline engine is considered to running at a perfect fuel to air ratio at 14.7, that means that 14 parts of air by weight to 1 part of gasoline.   I’ll forego the technical design of the oxygen sensor here, you can read up on it at Wikipedia.

Oxygen Sensor Operation

The PCM uses this voltage reading to make rapid minute corrections in the amount of fuel it injects into the engine. The PCM when it sees the voltage is too high, it knows the fuel mixture is too rich, so it reduces the amount of fuel it injects. Likewise, when the PCM sees the voltage is too low, it injects more fuel. This cycle repeats over and over as the engine is running.


This happens very rapidly to maintain a happy medium. If we use a scanner, a diagnostic tool that can “see” what the vehicles PCM is seeing, we can observe the voltage fluctuation on a graph.

Oxygen Sensor

Wiki says it best:

The sensor does not actually measure oxygen concentration, but rather the difference between the amount of oxygen in the exhaust gas and the amount of oxygen in air. Rich mixture causes an oxygen demand. This demand causes a voltage to build up, due to transportation of oxygen ions through the sensor layer. Lean mixture causes low voltage, since there is an oxygen excess.

Torque app - O2 Sensor Voltage

What you see on the graph is the up and down swing of the voltage output of the oxygen sensor; too rich, too lean, too rich, too lean, etc. This is the basics of how the oxygen sensor and the use of a computer work together to make the fuel system of your car deliver the best economy and power possible and still meet emission requirements.

Part 2 ~ Using this information in diagnosing problems or fault codes.

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