The mass airflow sensor’s purpose is to measure the mass amount of air entering the engine. The mass sensor is usually located on the intake inlet running to the intake manifold. Sometimes if there is a problem with it you can tap on it gently in the electronics area, and the engine should surge. There are multiple types of mass airflow sensors. Hot wire airflow meters use a current to keep a wire at a constant temp. The heat is carried away from the wire dependent on the airflow and temp. The ptc resistor varies with temperature change, as the temp drops so does the resistance. As the resistance changes the current has to increase to keep balance. This is sent to the ecu in a form of a voltage change. Another system is the hot film. It is very similar to the hot wire mass airflow meter. It heats a wheatstone bridge board, The air moves across the board and is measured on the back of the board. The thermistor measures the change in temp and thus the airflow change. The intake air temperature sensor also contributes to this equation being that humidity can slightly throw off the density reading. A vane airflow sensor simply rotates a flap as air comes in.
Micro turbine technology is a rapid learning front. Many of these very tiny turbines can be sandwiched together and can put out alot of power per size. Some are no larger than a dime. Because of this small size, they have the potential to replace batteries. The most common types are used in model aircraft to provide alot of thrust in a small lightweight package. These are usually a single turbine design but the cost is high on a turbine. The fuel efficiency was an issue at one time but now with advancements have become more efficient than piston engines! This is why they look so promising as a small portable battery charging devices. Materials other than metals have been used to minimize weight.
A knock sensor is generally used on turbocharged or high compression performance engines. The knock sensor is generally screwed into the engine block for all cars. To test the knock sensor, generally you can tap a wrench on it as it runs. The engine should change idle speed as the timing retards. If the idle speed doesn’t change, try again at a slightly higher rpm. If the speed once again dosen’t change the knock sensor probably doesn’t work. High performance engines are alot more prone to detonating when they are under boost. The timing on a turbocharged engine should retard when the boost comes on. If the boost would go too high the timing will be too advanced for the higher boost and will detonate. If the engine detonates it builds very high pressure waves. This can damage the engine’s pistons, bearings and crankshaft. The knock sensor senses the very high frequency pressure waves ocurring inside the cylinder. If the knock sensor is tightened too tight or is too loose it can effect the measurable frequency band. The tightening torque depends on the knock sensor specification for that engine. If it is incorrectly tightened it will sense other vibrations in the engine and incorrectly believe that there is a problem. The knock sensor works by simply retarding the timing until the detonaton quits. The driver should feel the significant decrease in power as it retards. It saves the engine from detonation which will break pistons and burn up head gaskets.
Ah the rumble of the american v-8. What a beautiful sound. If you haven’t owned one you should. Muscle cars are generally considered cars from the 60′s to 70′s and are domestic cars. The styling was beauty but the competition was in the engine. These were the cars that formed drag racing into what it is today. People would spend their last dollar to beat their buddies car by buying some aftermarket racing parts. It started with building small blocks and grew into crazy, large displacement big block engines. Some cars were in excess of 400 hp stock and made huge amounts of torque. Many cars like the mustang, chevelle ls-6, hemi cuda, challenger, buick gsx, pontiac gto and many other cars found huge followings as people competed against each other.
The crankshaft and camshaft sensors back each other up. If one does not work it could still run with the other one. If only one is present it wouldn’t. This gives the ecu or pcm away to know the timing of the engine. In older non injected cars the only timing needed was for the distributer to supply the engine with spark at the correct time. This was done mechanically and was usually assisted by vacuum at lower rpm to advance the spark timing curve. Then throttle body injection came along and the ecu needed to know when in the rotation to open injectors and which ones to open. The throttle body injection used a pulse off of the distributor to fire the injectors each time the engine made a revolution. Early injection systems used bank fire systems which injected fuel into certain cylinders one revolution then into the others on the next revolution. Newer systems are much more complex and need more information. That is where the camshaft sensor comes in. It will rotate twice for every one rotation of the crankshaft. By doing this it knows when each cylinder is coming up to top dead center on the compression stroke. This way it won’t fire on the opposing stroke to waste any fuel that could drop out on the cylinder wall, wasting fuel. It also now controls the spark ignition timing to each cylinder. The ecu now distributes the spark instead of the distributor. The coil packs are now on top of the spark plugs instead of a single coil being inside the distributor.
Both these sensors have a similar function but are slightly different in function. A barometric or baro sensor tells the absolute atmospheric pressure. The map sensor uses a relative vacuum measurement and has a different range. The map is important for many reasons and usually every fuel injected vehicle will have one of these. The baro sensor is used as a secondary system so that even slight atmospheric changes can be monitered by the engine. Air density changes, as the pressure increases the engine will go lean. The sensor tells the ecu, which adds fuel to correct the lean condition. If your map sensor seems to be malfunctioning you can test it. First check for a loose plug or a bad vacuum hose.