The TPS (throttle position sensor) does exactly what the name implies. It looks at how hard your are stepping on the throttle so that it knows how hard the engine is working. The fuel injection map, which tells the injectors how much fuel the engine needs, is determined by two functions, throttle position and rpm. The throttle position sensor is a variable resistor, meaning as the sensor rotates on the throttle shaft, the voltage value going back to the computer is changing. Normally from idle the voltage is close to zero and climbs to around five volts at wide open throttle. The tps is on one side of the throttle shaft, on the throttle body. Just have someone step on the gas pedal and watch the only part under your hood that rotates, it will be on one end of the moving shaft. If there is a problem with your TPS sensor you can test it. First inspect the plug to make sure it is tight. Also check that the plug wires are not cracked or broken. Now remove the sensor plug. Use a volt/ohm meter and set the range to 20k ohms. Next touch one lead to the center pin in the plug and the other to one of the outer pins. Slowly rotate the throttle until it’s wide open. The ohm’s should have been smoothly climbing or dropping as the throttle was moving. If the reading was jumpy and didn’t change smoothly, replace the sensor.
The catalytic converter “cat” for short was developed back when carburetor was still being used on production vehicles. They were made to clean up hc or hydrocarbon emissions (unburnt gas) They do so by means of a catalytic reaction, meaning the hc’s chemically change to something not harmful. Catalytic converters have progressed through the years. At one time they had an air tube running to them, because the have to stay close to a correct air to fuel ratio. They would regulate air to control the reaction so that the catalyst would not overheat and burn up. Cats also need some heat to work properly, and do not do well at startup. This is why some manufacturers have had to add pre-cats that heat up quickly so that they pass manufacturer emission requirements. catalytic converters can sometimes malfunction and cause the engine to run poorly and not have much power. Usually if your driving up the interstate and pull over to look under the car it will be glowing if the cat is plugged up. Unfortunately the only true test is to remove it and look inside of the converter. The converters either have beads in them or normally have honeycomb layers. If damaged pieces will probably be turned sideways or fall out when you remove them. Many times you can replace your converter for cheaper, if you use an aftermarket high flow converter. The high flow catalitic converter will probably give you better fuel economy and power due to less restriction. High flow catalitic converters are also safe to pass emission tests if you are required to do so.
Fuel injection has become popular due to the emission restrictions made by the epa. The fuel can be controlled much more precisely, due to all the information presented by the sensors to the ecu. There are different types of fuel injection systems. The first progression was to a throttle body setup. The system was simple and had the advantages of precise control. Unfortunately this system has alot of short comings, being that the fuel was being put in the engine in the same location as the carb. The problem with this is that the fuel “puddles” or drops out of suspension and collects on the intake manifold walls. As the engine demands more power (air) the extra airflow pulls the puddled fuel into the cylinders. When the engine stays at a constant speed the ratio moves from lean to rich inconsistantly. Another problem with this setup is that the fuel still travels through the manifold. Intake manifolds are inconsistent and often flow different amounts of air into different cylinders. This leads to cylinders changing from rich to lean.
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Carburetors or carbs for short, have been a way of controlling fueling of engines from the beginning and are still used today in racing such as nascar. The simplicity and ease of tuning is still a favorite of many racing sanctions that dont want to worry about traction control and various other forms of trickery from being hidden inside fuel control boxes. Carbs work off the venturi affect, while the engine is running it is moving air out of the exhaust. On the intake side the engine developes a vacuum. As the air rushes in the carb the diameter of the air opening gets smaller in the middle of the carb. The fuel outlets will be located at the smallest diameter called the venturi. The air coming in the engine must accelerate as it passes through the venturi, trying to fill the vacuum in the intake manifold. The venturi is where the fuel will expel, due to the vacuum being created by the acceleration of the air. The jets, which control the fuel flow are located upstream of the outlets. Most carbs have a low rpm circuit and a high rpm jets called pilot or idle jets and main jets. Like everything in an engine if the carb flows more air it has the ability to make a huge difference in power. Some stock carbs such as carter, webber and quadrajet were a little more complex due to the car manufacturer having to have precise fuel control for emissions compliance. Most racing sanctions such as nascar and nhra use holly carbs for their simplistic nature to tune.
EGR stands for exhaust gas recirculation. It was one of the first methods deployed to fight high nox values. The valve allows a controlled amount of exhaust to be sent back into the intake of the engine. The exhaust has a high content of carbon dioxide and inhibits the peak combustion pressure thus reducing nox. By using this method car manufacturers are allowed to use higher compression ratios. The recirculation occurs in the lower to mid rpm range. The recirculation stops the enging from knocking (detonating) at part throttle, high load conditions. The egr isn’t used or very little at idle. The combustion pressures are not very high due to low engine speed. Also at a little less than full throttle the egr disengages. By disengaging it allows the combustion pressures to raise and make more power. The engine will not detonate at full throttle, unlike part throttle conditions the fuel ratio will be very rich at or close to full throttle to make power.
Electronic fuel injection or EFI is a way of controlling the amount of fuel being used by the engine in all types of conditions. Mechanical fuel injection was an earlier version used by spark ignited engines. Mechanical injection is still used on diesel engines often. Most spark ignited engines use electronic fuel injecton due to the adjustability and precision of the electronics involved. The sensors send all different types of information back to the ecu (computer) then it computes from a internal map what the value should at that paticular point. The map, as it’s called, is just a huge directory of numeric values. These values tell the injectors when and how long to stay open. The longer they stay open the more fuel gets sprayed into the engine. The fuel pressure can affect the overall map by shifting it up or down.
Emissions components consist of parts of an engine that their only function is to clean the amount of emissions that are expelled from the engine. The catalytic converter has the job of trying to clean up the unburned gas from the exhaust. Air pumps would also help out with this job by injecting air into the engine’s exhaust manifold. The hot unburned fuel would immediately ignite in the presence of fresh oxygen. The unburned fuel is called HC or hydrocarbons. This is usually the hardest pollutant to keep low and is why all cars run fuel injection. The CO or carbon monoxide is controlled by keeping the air to fuel ratio correct and getting a clean burn in the chamber. NOX or oxides of nitrogen are caused by the high pressures and temperatures of combustion in the chamber. The EGR or exhaust gas re circulation valve lowers the NOX by injecting a small amount of exhaust into the intake air. The exhaust has low oxygen and CO in it. These make the combustion pressures and temperatures lower, lowering NOX. The O2 or oxygen sensor tells the computer if the AFR or air to fuel ratio is correct. If the ratio is wrong in the exhaust it will adjust the fuel injection until it’s correct.
