The air temp sensor simply checks the temperature of the incoming air. The sensor is usually located on the air box (filter area) or somewhere in the air inlet tube. The purpose of the sensor is to help with calculations of air density coming into the engine. The information is fed to the computer. If the air is warmer it’s less dense and requires less fuel for the engine to run at it’s correct air to fuel ratio. The engine needs more fuel at colder temps due to the denser air. The colder denser air gives the engine the ability to make more power, needing more fuel. The air temp sensor changes resistance with heat changes and will send the new voltage to the ecu. The car’s computer then changes the amount of fuel injected in the engine. If you have a problem with your air temperature sensor, you can test it. First check the plug to make sure the wires look good and the plug is tight. Run the car for five minutes. Shut off the car and remove the sensors plug. You will need a volt/ohm meter to check the ohms. Set the ohm meter on 20k ohms. There are three types of temperature plugs. With a single wire sensor, touch the one wire and use the other wire to touch the brass or metal on the sensor. Two wire sensor, just touch the two wires. Three wire temp sensor, touch the center and one of the outers. The ohm value should be higher than 500 ohms or it is not good and needs to be replaced.
A fuel pressure reguator maintains a certain pressure always. The fuel pressure regulator is usually located on the end of the fuel rail. The fuel rail covers the fuel injectors. The regulator has a fuel line running off it back to the fuel tank. The regulator has a little valve in it and pressure is controlled by the spring tension that keeps it closed. Simple adjustable regulators use a bolt that runs inside the regulator, to add tension on to the spring and valve. If the pressure is too high the fuel that escapes around the valve and returns to the gas tank. This always keeps the pressure constant. Adjustable fuel pressure regulators for turbo or supercharged vehicles are different. As the boost increases the demand for fuel becomes greater for the engine. To increase the fuel to the engine the fuel pressure is increased. The boost created by the compressor is fed to the back side of the valve. It is the same side as the spring. The increased pressure on the backside of the valve holds it shut more, increasing the pressure according to the boost. There is usually still an adjustment for the static or regular pressure.This allows the unboosted curve to be richened up.
The electric fuel pump is generally used on fuel injected cars. It has a relay under the hood, usually on the inner fender, which supplies 12 volts dc to the pump. It should click every time the key is turned to a forward position. The starter does not have to engage for this to happen. If someone turns the key forward for you, you will be able to hear it clicking under the hood, assuming it works. If it is clicking you can still check it. One of the leads should have no voltage then switch to at least 12 volts when the key is turned. This action primes the pump and builds fuel pressure up so the engine can start. The pump itself is usually located inside the gas tank, so that it is cooled down by the fuel. The fuel pump delivers about 7 psi to throttle body injected engines.
(Full Article)
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.
(Full Article)
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.
