FUEL INJECTION BASICS
Hot Rods, Sand Rails, Drag Cars, Off Road Trucks and Boats.
The fundamentals of the 4-stroke internal combustion engine haven't changed since its invention - it's still suck, squeeze, bang, blow; and the engine still needs just three things to run: air, fuel, and spark. How well it runs, and how much power it makes still depends on combining these three things in the right proportions at the right time. The more you step on the throttle pedal, the more the throttle blade opens, and the more air enters the engine. Feeding an engine the right amount of fuel is basically a function of engine load - the more load on the engine, the more fuel it needs. Spark timing is basically a function of engine speed - the faster the engine speed, the earlier in the "squeeze" (compression stroke) the spark must be fired.
In today's modern EFI engines, fuel and spark delivery are controlled by a computer or Electronic Control Module (ECM). Fuel is delivered, or injected, directly into the cylinders by fuel injectors. Fuel injectors are nothing more than highly sensitive and accurate valves - they are supplied fuel by the fuel rail at a constant pressure, and have a calibrated orifice, or opening. The computer fuels the engine by telling the injectors when to "fire" (open and deliver fuel), and controls how much fuel is delivered by how long it tells the injector to stay open. Spark timing is similarly controlled by the computer. In the case of the LS2, which has individual ignition coils for each cylinder, the computer simply tells each coil when to "fire" and thereby create a spark across the spark-plug electrodes which, of course, ignites the fuel-air mixture in the cylinder and begins the "bang", or compression stroke, which is what makes power at the crank.