Engine Maintenance and Modification Bradley Artigue
FIAT 124 Spider Engine Maintenance + Modification - Artigue.com
FIAT 124 Spider Engine Maintenance + Modification - Artigue.com
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FIAT 124 Spider<br />
<strong>Engine</strong> <strong>Maintenance</strong> + <strong>Modification</strong><br />
The FIAT implementation of the Bosch L-Jetronic fuel injection system is relatively<br />
simple <strong>and</strong> uses the most basic components required to operate the system. Many<br />
additional options including atmospheric pressure sensors, knock sensors, <strong>and</strong> crank<br />
angle sensors, are all possibilities with L-Jetronic but were never installed. FIAT quite<br />
literally built a system around the existing 2000cc carbureted engine. The simplicity<br />
results in a system that is inexpensive, easy to diagnose, <strong>and</strong> can be repaired by the<br />
home mechanic. The system consists of a number of components that are located in<br />
the engine <strong>and</strong> passenger compartments. Figure 33 summarizes the major components<br />
<strong>and</strong> some of their connections.<br />
5.2 The Air Flow Meter <strong>and</strong> Fuel Pump<br />
The air flow meter is positioned just above the air filter <strong>and</strong> is the only point of entry for<br />
air into the fuel injection system. Inside is a spring-tensioned flap connected to a<br />
rheostat. As intake air volume increases the flap moves an arm against the rheostat.<br />
The rheostat converts the movement of the flap into an electrical current that is sent to<br />
the fuel injection computer <strong>and</strong> is the primary input in the system. Fuel is delivered in<br />
proportion to the volume of air <strong>and</strong> the fuel injection computer adjusts the fuel delivery<br />
to best find the 14.7:1 air to fuel ratio.<br />
The stream of new air passes through the main air hose (also called the “big air hose”),<br />
connecting to the throttle body. The operation is abbreviated as follows:<br />
1. Air passes the throttle plate into the plenum (the square aluminum box on the<br />
engine intake side) <strong>and</strong> is drawn through runners (pipes under the plenum) into<br />
the engine.<br />
2. The fuel injection computer opens the injectors <strong>and</strong> sprays fuel into the intake<br />
runners (the four tubes between the plenum <strong>and</strong> the cylinder head). All four<br />
injectors fire at the same time.<br />
3. Valves open <strong>and</strong> draw the mixture into the combustion chamber.<br />
4. The mixture is compressed <strong>and</strong> explodes via ignition spark.<br />
5. The mixture is expelled.<br />
6. An oxygen sensor measures the amount of unburned oxygen in the exhaust.<br />
7. The F.I. computer uses the reading from the oxygen sensor to adjust the next<br />
mixture.<br />
40