FIAT 124 Spider
Engine Maintenance + Modification
44
the computer to increase the amount of fuel. The system will also increase or decrease
the amount of fuel based on the temperature of the air entering the system.
5.7 The Oxygen Sensor
A final sensor performs continuous monitoring of the exhaust gases. This input is used
by the computer to adjust fuel flow to best reach lambda. The oxygen sensor, also
known as a lambda sensor, is a ceramic and platinum electrode. The ceramic permits
diffusion of the oxygen present in the air. At engine operating temperatures it becomes
conductive; when the level of oxygen on one side of the electrode is different from that
on the other side a voltage is generated. This voltage is reported back to the fuel
injection computer. Sensor operation becomes effective at temperatures above 350
degrees Celsius; below this range the fuel injection computer receives no meaningful
input. Many vehicles employ heated oxygen sensors that output data to the computer
much faster; the FIAT uses the unheated type.
5.8 Other Components
If you flip back to the overview diagram (figure 33) you’ll notice a number of other fuel
injection pieces and parts that we did not cover. Some of them, such as the air
conditioner bypass valve, exist to provide extra air into the plenum when a load (such as
the a/c compressor) is switched on. Rarely do FIAT Spiders even have this valve, but if
you have the aftermarket air conditioner it may be fitted. You’ll also notice the fuel
delivery components, the fuel pump, fuel filter, fuel manifold, and fuel pressure
regulator. These are responsible for fuel delivery (pump), filtering (filter), routing
(manifold) and maintaining constant flow rates to each injector (regulator). The regulator
keeps the flow constant by increasing fuel pressure and manifold pressure is near
ambient and dropping pressure as the manifold vacuum increases.
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