Repair 7

In an internal combustion engine, the exhaust manifold collects the products of combustion (exhaust gases) from two or more cylinders and conducts these to a single exhaust pipe.

Design

Typically made of stainless steel, cast-iron or heavy-gauge steel, the exhaust manifold directs exhaust gases from multiple cylinders to a single exhaust pipe. In so doing, the exhaust manifold also helps to minimize leakage of heat, air and gases. Copper gaskets connecting the manifold to the cylinder heads can be used to create a more airtight system, though these are not necessary.

Benefits

By minimizing the loss of heat, the exhaust manifold reduces the temperature under the hood. This helps to prevent overheating and damage to heat-sensitive parts while increasing power by reducing the temperature of the intake manifold. As gases move more quickly in higher temperatures, the exhaust manifold helps to increase the speed at which exhaust leaves the system.

Limits

As cylinders fire at different times, an ideal exhaust manifold would contain pipes of different lengths to ensure that exhaust gases from one cylinder have been cleared from the system before another fires (i.e., to prevent back pressure). Due to space limitations, however, exhaust manifolds typically contain short pipes of uniform length. Though compact, this design increases back pressure, subsequently increasing heat loss under the hood and reducing engine performance.

Sophisticated computers that continuously adjust critical engine parameters control almost all modern car and truck engines. The crankshaft sensor is one of the numerous sensors that feed information to the computer.

Function

The crankshaft sensor sends information to the engine computer about the precise position and speed of the crankshaft. Because the crankshaft is attached to the pistons, information about its position allows the computer to determine the relative positions of all critical engine components, including pistons, belts and valves. This makes it possible to time the injection of fuel and the spark plug ignition for optimum performance and fuel economy.

Principle of Action

The crankshaft sensor consists of a metal disk positioned on the crankshaft and a detector that covers a magnetic coil. The metal disks movement past the coil causes a disturbance in the magnetic field, creating a stream of electric pulses that the computer uses to determine the speed and position of the crankshaft. The sensor does not produce direct data about the location and speed of the crankshaft; it sends raw data to the engine computer, which then calculates the desired values.

Malfunction

A malfunctioning crankshaft sensor can cause various disturbances including extended crank time during start-up, rough running, bucking, compromised fuel economy and stalling. If your vehicle is equipped with an on-board diagnostic computer, a malfunction of the crankshaft sensor will trigger an error code to inform you about the problem.

A catalytic converter is an exhaust emissions device used to lower a vehicles exhaust emissions output. Similar in size and shape to an exhaust muffler, a catalytic converter is attached directly to a vehicles exhaust system. What follows is a brief description outlining the main purposes of catalytic converter use.

Burn Unbruned Exhaust Gases

The main function of a catalytic converter is to burn unburned exhaust gases that exit a vehicles engine. By burning these unburned exhaust gases, a catalytic converter lowers the emissions output of a vehicles exhaust.

Impede Normal Exhaust Flow

A catalytic converter creates exhaust system impedance, which causes the exhaust exiting a vehicles engine to slow down, a process that gives the catalytic converter more time to act upon the exhaust gases.

Reduce Hydrocarbon Exhaust Emissions

Hydrocarbon emissions, which are created when air and gas is burned inside of a vehicle engine, are significantly reduced by the burning action of a catalytic converter.

Mandate Unleaded Gasoline Use

All vehicles equipped with catalytic converters require the use of unleaded gasoline, which is a cleaner-burning type of gasoline that results in lower exhaust emissions. Leaded gasolines and/or racing gasolines are highly damaging to a catalytic converter and cannot be used in cars equipped with one.

Reduce Carbon Monoxide Emissions

Carbon monoxide exhaust emissions are significantly reduced by the burning actions of a catalytic converter. Carbon monoxide gases are natural by-products of engine combustion, and catalytic converters help to lower these emissions by re-burning exiting engine exhaust gases.

The positive crankcase ventilation valve, PCV for short, is an "L"-shaped mechanical component found in vehicles that assists in returning gasses from the engines crankcase, where gasoline is used.

Significance

The PCV valve is just one part of the PCV system, which uses both optimal gasoline performance and is better for the environment. Instead of allowing fumes from the gasoline to ventilate into the atmosphere, the PCV valve sends the gasses back into the combustion chamber to be used again as additional fuel.

Location

The location of the PCV valve within a vehicle brand and model varies with each company. For the 1997 Nissan Altima, the PCV valve is under the hood of the vehicle, in the upper engine area, found mounted in the intake manifold. Most vehicles follow the same PCV placement by the engine, but exact specifications can alternate.

Appearance

The PCV valve is most commonly part plastic and part metal. The valve has two parts: a vacuum on one end that suctions gasses back to the intake manifold, and a metal sphere inside the valve corner, aiding in efficient transfer of gasses.