How the Engine Works

How modern Engines work Presented by Auto Service Tech.com copyright 2008 by peter F. Meier Gasoline Engines, like these... still work in basically the same way as this one... they all take in air add fuel, compress the mixture and then ignite it to produce power. The difference is all about what comes out of the tailpipe. And on today's cars, that's controlled by this guy... this is the Engine Control Module A computer that controls how much fuel gets in, and when it is ignited. That's a bit of an over simplification. The ECM is charged with keeping everything in order to reduce emissions. On many cars, the ECM also controls the transmission. It is then called a PCM, or powertrain control module. It's a complicated device, but simple in operation. It takes in information from a variety of "sensors", then falls back on its programming to operate the engine's systems... the crankshaft position sensor tells the ECM where the pistons are in their travel... while camshaft position sensors like the next two examples tell the ECM where the valves are... the ECM uses this information to determine when to determine when to add fuel and fire the spark plugs... now let's start with getting the air in... Air flows in through the air filter, the intake boot, and then through the Throttle Body. Unlike old cars with carburetors, the Throttle Body only allows air flow. You aren't "giving it gas" when you step on the "gas" pedal! Remember, that's the ECM's job! But it needs a lot of information to do that. Like... How much air is going in? Fuel is mixed with air in a proportion of roughly 14.7 to 1 one method of telling the ECM how much air is getting in is through this sensor... that's 14.7 pounds of air to 1 pounds of fuel for a gasoline engine! It's called the Mass Air Flow sensor, or MAF and it can precisely measure the weight or MASS of air passing through it. Some car use this sensor instead... this is a manifold absolute pressure sensor it measures the "absolute" pressure in the intake manifold. The ECM used this information in combination with others to calculate the mass of air. But that's not all it needs to know... How cold is the air? How warm is the engine? How thick is the air? Other sensors on the car provide this data to the ECM. Once the ECM has the info on the air getting in, it can calculate how much fuel to add. Then it's time for these guys... These are the fuel injectors... the final delivery point of fuel to the engine. It all start with the fuel pump, through the fuel filter and lines to the furl rail... The ECM controls fuel amount by controlling how long the injector is held open... but age, wear and tear, and other factors make the ECM's choice a highly educated guess... the ECM needs "feedback" on how well it did its job. That's what this sensor does... this is the Oxygen sensor but it's really nothing of the kind... Located in the exhaust before the catalytic converter, it reacts to the changing oxygen content present more like a "switch" if the mixture was too "rich", the sensor produces a voltage of approx. 1.0 volts... and if it's too "lean", it produces a low voltage... approx. 0.1 volts. So the ECM is constantly questioning the oxygen sensor to see what it saw... and adjusts the injector opening in response. It the first "shot" was too little, the 02 sensor reads low... and the ECM responds by adding a little more on the next "shot" ... on the second "shot", the 02 will read high... and the ECM will respond by adding less on the third "shot".... It is this constant "back and forth" the ECM that allows the 02 sensor to "switch", which in turn... allows the ECM to maintain control over the fuel supplied to the engine, and keep it in the right ratio.. Or mixture... range. There is also an oxygen on the other side of the cat... this is primarily to keep an eye on the catalytic converter's health... but what a minute... we haven't ignited the mixture yet... that's the job of the spark plug... and the ignition system... While there are a few different types... like this coil on plug system... or this distributorless lgnition system ( DIS for short)... and this electronic distributor system... They all do the same thing... provide a high energy spark at the right time... you can make the ignition systems job easier... by maintaining your spark plugs... Excessively worn plug force the system to work at its maximum... and that leads to premature failure of the coils... there are other emissions systems included on modern cars like... Exhaust Gas recirculation system... EGR, for short... and system to keep the fuel vapors contained... EVAP is their name... and additional systems unique to manufacturer and model... but that covers the basics on how a modern engine works. Hope you enjoyed the tour! How modern engines work