Automotive

FUEL SYSTEM

The purpose of the fuel system is to supply the right amount of fuel for the engine to burn, and control the speed of the engine. Two types of fuel systems have been used in gasoline engines in modern times: Carburetors Fuel Injection Parts of the fuel supply system: Gas Tank The gas tank is usually made of two pieces of stamped steel, spot welded together to form a container, or it can be made of plastic. It may have baffles inside to keep gas from sloshing around. It will have a fuel pickup located at the deepest part, a filler neck, a vent to allow air back in when the fuel is removed, and it will have a gauge to give the driver information on fuel level. Many cars have the fuel pump located in the gas tank. This keeps a normally noisy electric fuel pump quiet. The gas tank can be located in many different locations. Safety should enter into the design of the location of the gas tank, but safety often takes a back seat to profit. All manufacturers have been guilty of poor gas tank locations at one time or another. Examples are the Ford Pinto, and the Chevrolet & GMC C/K Pickup truck from 1973 - 1988. Both were notorious for having their gas tanks explode in a relatively minor accident. The safest place for a gas tank is somewhere within the perimeter of the four wheels. Gas tanks could be made crash proof ( fuel cells used in race cars are designed not to explode ) but again , profits often win over safety. Fuel Lines and vent lines Galvanized steel fuel lines carry the fuel from the tank to the engine. Manufacturers try to minimize the amount of rubber line used, because rubber deteriorates over time, but some rubber lines must be used to allow the engine to flex on its' mounts. From 1972 model year on, the gas tank and carburetor float bowl have been vented into a charcoal canister under the hood, so a vent line runs forward from the tank, to the canister. Most fuel injection systems vent the excess fuel supplied by the pump, but not used by the engine, back into the tank by a fuel return line. Fuel Pump Two types of fuel pumps are used in modern cars: Mechanical Pump -driven by the engine itself. Usually by an eccentric (cam) on the camshaft. The cam pushes down on a rocker arm which pulls up on a pull rod compressing a spring, pulling up the diaphragm, and filling the pump chamber with fuel. When the cam turns, and releases the rocker, the spring is able to push down on the diaphragm, pumping the fuel to the carburetor. Pump pressure is regulated by the tension of the spring. Electric Pump -can be mounted anywhere in the fuel line, but in modern cars is usually submerged in the gas tank. This keeps them cool, and quiet. Be aware that an electric fuel pump will supply a certain amount of pressure, and are different between an engine using a carburetor, and one using fuel injection. Pumps for fuel injection run fuel pressures of from 30 to 75 PSI, whereas on for a carburetor will only supply from 3 to 7 PSI. They are not interchangeable. Electric pumps can be solenoid types which work similar to a mechanical pump, but

instead of a cam moving the diaphragm, an electric solenoid does the work; or they can be an impeller type which uses an electric motor to drive a little impeller wheel. Fuel pressure is regulated by a pressure regulator located on the end of the fuel supply rail on the engine.

Carburetors 2 Jobs: Mixes air and fuel together in the correct proportion under all conditions. Regulates the speed of the engine. The carburetor must mix the air and fuel together in the correct proportions under all conditions, and those conditions change depending upon whether the engine is cold or hot, idling or at high RPM, accelerating, decelerating, or staying the same speed. To deal with those changing conditions, the carb has different "circuits". Air fuel ratio will need to be anywhere from 8:1 to 15:1 by weight. We are not used to thinking about air as having weight, so if it was described by volume one gallon of fuel would need approximately 15,000 gallons of air to burn it. To help us understand how a carb works, we are going to "build" one. We'll start with a tube or pipe for the air to go through, called an "air horn". We'll mount it on an intake manifold sp one carb will feed all our cylinders, otherwise, we'd have to use a separate carb for each cylinder.

We'll put a mounting flange on the bottom, and where the manifold meets the head, and put gaskets in between the flanges, so that the only way air can get into the cylinder, is through the air horn. Install a small reservoir called a float bowl (6),off the side of the air horn (1), to hold the gas before it goes into the air horn. We will maintain the level of fuel in the float bowl with a float which rides up and down on the gas (7).

The float controls a needle (4) and seat (3) which shuts off the gas when float level is reached. A vent (2) allows atmospheric pressure to act on the fuel in the float bowl so we don't get a vacuum created and starve the engine for gas. The float can be made of hollow brass, or foam. Somehow, we have to get the gas from the float bowl into the air horn, this is done with a main discharge tube.

Notice how the one end of the main discharge tube is in the bottom of the float bowl, and the other is in the air horn, with the nozzle just above float level. We also need the amount of gas to increase with the amount of air. Bernoille's principle states that: "When the speed of an air stream increases, its pressure decreases". What this means is that if you force a stream of air to speed up, a vacuum is created in it. This is the same principle that allows airplanes to fly. The top of the wing is a curved surface, while the bottom is flat. As the wing moves through the air, the air moving over the wing speeds up, while the air moving under the wing stays the same speed. This creates a vacuum over the wing (lift). When the lift is greater than the weight of the aircraft, it will fly. In a carburetor, we put a smaller version of an airplane's wing around the main discharge

tube, just above float level. We call this restriction, a "venturi". The faster the air moves through the venturi, the more vacuum is created in it.

There is a pressure differential between the float bowl and the venturi, and so the fuel flows out the main discharge tube and into the air stream. The fuel is drawn up from float level, and out into the air stream where it forms tiny droplets and vapourizes. The faster the air flows, the more fuel comes out. If a smaller venturi is added inside the main venturi, venturi vacuum is increased.

A venturi is simply a restriction in the air horn that forces the air to speed up when it goes through it. The faster the air goes through, the more fuel comes out. This is called "venturi vacuum" and is greatest at fastest air flow.

An "air bleed" causes the fuel to break up into smaller droplets to vapourize better. the smaller the droplets we can break the gas into, the faster it will vapourize. Remember : An engine runs on gasoline vapour, not liquid. Droplets are still a liquid.

A "main jet " is added to the bottom end of the main discharge tube to limit the amount of fuel. The main jet is just a screw in brass plug with a hole drilled in it. The larger the hole is, the more gas will pass through it, so the richer the air - fuel ratio will be. If you want a leaner air - fuel ratio, put in a smaller main jet. We need to control engine speed.

This is done by restricting the flow of air into the engine by putting a shaft through the body of the carb, and placing a disc on the shaft. This is the "throttle plate". When it is placed across the

air horn, it restricts the air flow and therefore, engine speed. When the plate is moved parallel to the air flow, there is no restriction, and therefore, the engine speeds up. Any restriction in the air flow creates a vacuum in behind the restriction. Remember the venturi; at high airflow, the venturi was a restriction, and therefore venturi vacuum was created in the venturi. At low airflow the venturi was not a restriction, the air passed through it easily. At closed throttle, the throttle plate restricts the amount of air getting into the engine, and therefore a vacuum is created downstream from the throttle plate. This is called "manifold vacuum". Manifold vacuum is greatest at closed throttle, and is least at wide open throttle. Manifold vacuum and venturi vacuum work opposite each other. When manifold vacuum is high, venturi vacuum is low, and vice versa. Our carburetor would now work. If we took our drawing down to the metalwork shop, built our carb, and bolted it on an engine, the engine would run. It wouldn't start very well, if at all,....it wouldn't idle,.......it wouldn't run at low speed,....... it wouldn't produce much power,........it wouldn't accelerate......, but if all we wanted to do was drive down the road at 40 MPH it would run! Obviously our carb still needs some work. We will go through it and solve its drivability problems one by one. First Problem: - the engine is difficult to start especially when it is cold, and doesn't run well until it is warm. Why? - an engine runs on fuel vapour. Liquids don't burn. The problem with gasoline is that it is a liquid. Before we can get it to burn, we must mix it with air. Gasoline vapourizes very well at high temperatures, but not at low temperatures. Solution : The Choke System Because only a 50% of the fuel vapourizes, we must add twice as much to make sure there is enough to burn. A butterfly valve is added above the venturi, so that when the choke valve is shut, engine vacuum acts on the main discharge tube to draw a huge amount of air into the air stream Engine cranking speed is from 150 to 300 RPM, so at that speed, the engine's fuel requirement is low. The main circuit is capable of supplying enough gas to allow the engine to run at 2500RPM, so it can easily supply enough fuel for a rich mixture on start. When the engine is cranking over cold, the choke plate should be shut tight, and a huge amount of fuel enters the air stream.

This mixture is the richest mixture of all, and is around 8 : 1. In the drawing above, the choke shaft is centered on the butterfly valve. This is, in fact, incorrect. This would mean that that

choke plate would not open when the engine starts, it would remain shut, and the engine would starve for air. The shaft is really not on center, but off towards one side, so the choke plate opens slightly when the engine starts. this allows a leaner air - fuel ratio of around 10:1 when the engine starts. Because of the extremely rich mixture on choke, it is very easy to "flood" the engine. This is when there is so much liquid fuel in the combustion chamber that there is not enough air to support the combustion and the engine won't run. A choke "unloader" opens the choke plate when the throttle is depressed all the way. This allows the maximum amount of air through the engine to clear out all the extra gas, and allow the engine to start. Choke Operation: Manual - a cable runs to the choke so when the driver pulls on a knob on the dash, the choke plate shuts. The worst thing about a manual choke, is that the driver forgets to turn it off. Automatic - A bi-metallic or thermostatic coil, which is sensitive to heat closes the choke plate when the engine is cold. When the coil heats up, it allows the off - center shaft, and a vacuum device called a "vacuum break", to open the choke. As the engine heats up, the choke plate automatically opens the choke up, leaning out the mixture. The bi - metallic coil has to be heated somehow. It can be heated by heat from the exhaust pipe, electrically, or by water from the cooling system. Fast Idle Because of the poor vapourization of fuel, poor fitting engine parts, thick oil, and extra friction inside the engine when cold, the engine would stall at idle if it was left the same as it was when hot. A "fast idle cam" opens the throttle slightly when the choke is on to prevent stalling. Heat Riser Valve When the engine is cold, a "Heat Riser Valve" forces hot exhaust gas to circulate under the carb, and around the intake manifold to warm it up, and help the fuel vapourize better. Thermostatic Air Cleaner From 1968 on, most cars have used an air cleaner that draws hot air from a stove, or cover, around the exhaust manifold, to help vapourize the fuel better when the engine is cold. When the engine heats up, a thermostatic switch opens the cold air intake for better gas mileage.

Fuel Injection Virtually all cars sold in North America have use electronic, computer controlled fuel injection to supply the fuel to the engine. Fuel injection gives better fuel economy, with more power and lower exhaust emissions, and better drivability. The computer has transformed the fuel system. Fuel Supply Electric fuel pumps can be located anywhere in the fuel system, but since any pump pushes better than it sucks, it makes more sense to locate it as close to the source of the fuel as possible. Most manufacturers locate the fuel pump in the fuel tank, below the level of the gas in the tank. Fuel pumps located in the tank are usually impeller type pumps whereas pumps located in the fuel lines are usually bellows type pumps. Because the pump will continue to run with the engine shut off, a relay controls the pump to make sure that doesn't happen. A roll over switch shuts the pump off in event of an accident. Details on its location, and procedure for re-setting it, will be in the service manual.

A motor drives a little vaned wheel like a water wheel called an impeller type pump. Liquid keeps the pump cool, so its important you don't let the fuel level get too low, or the pump burns out. The pump itself can be worth as much as $400.00, and two or three hours of labour to drop the tank and replace the pump.

Fuel is forced through a folded paper filter located somewhere between the pump and the fuel rail. Steel fuel lines and braided hoses route the fuel under the car body to the fuel rail on the engine. Fuel pressure is considerably higher when the car is equipped with fuel injection, so the lines and filter must be able to withstand more pressure. The fuel rail feeds fuel to the individual fuel injectors in a multi port system. A Shrader valve (like a tire valve) allows the technician to check fuel pressure in the system. A fuel pressure regulator maintains fuel pressure to the injectors at a constant value even though manifold vacuum and voltage to the pump are constantly changing. Fuel pressure in a carbureted system can be as from 1 to 7 psi. Fuel pressure in a fuel injected gasoline engine can be from about 35 to 75 psi. Fuel pressure in a diesel engine can be more than 600psi!

EXHAUST SYSTEM An exhaust system is usually piping used to guide reaction exhaust gases away from a controlled combustion inside an engine or stove. The entire system conveys burnt gases from the engine and includes one or more exhaust pipes. Depending on the overall system design, the exhaust gas may flow through one or more of:    

Cylinder head and exhaust manifold A turbocharger to increase engine power. A catalytic converter to reduce air pollution. A muffler (North America) / silencer (Europe), to reduce noise.

Manifold or header

Aftermarket exhaust manifold In most production engines, the manifold is an assembly designed to collect the exhaust gas from two or more cylinders into one pipe. Manifolds are often made of cast iron in stock production cars, and may have material-saving design features such as to use the least metal, to occupy the least space necessary, or have the lowest production cost. These design restrictions often result in a design that is cost effective but that does not do the most efficient job of venting the gases from the engine. Inefficiencies generally occur due to the nature of the combustion engine and its cylinders. Since cylinders fire at different times, exhaust leaves them at different times, and pressure waves from gas emerging from one cylinder might not be completely vacated through the exhaust system when another comes. This creates a back pressure and restriction in the engine's exhaust system that can restrict the engine's true performance possibilities. A header (sometimes called extractor in Australia) is a manifold specifically designed for performance.[1] During design, engineers create a manifold without regard to weight or cost but instead for optimal flow of the exhaust gases. This design results in a header that is more efficient at scavengingthe exhaust from the cylinders. Headers are generally circular steel tubing with bends and folds calculated to make the paths from each cylinder's exhaust port to the common outlet all equal length, and joined at narrow angles to encourage pressure waves to flow through the outlet, and not back towards other cylinders. In a set of tuned headers the pipe lengths are carefully calculated to enhance exhaust flow in a particular engine revolutions per minute range. Headers are generally made by aftermarket automotive companies, but sometimes can be bought from the high-performance parts department at car dealerships. Generally, most car

performance enthusiasts buy aftermarket headers made by companies solely focused on producing reliable, cost-effective well-designed headers specifically for their car. Headers can also be custom designed by a custom shop. Due to the advanced materials that some aftermarket headers are made of, this can be expensive. Luckily, an exhaust system can be custom built for any car, and generally is not specific to the car's motor or design except for needing to properly connect solidly to the engine. This is usually accomplished by correct sizing in the design stage, and selecting a proper gasket type and size for the engine. Header-back The Header-back (or header back) is the part of the exhaust system from the outlet of the header to the final vent to open air — everything from the header back. Header-back systems are generally produced as aftermarket performance systems for cars without turbochargers. Turbo-back The Turbo-back (or turbo back) is the part of the exhaust system from the outlet of a turbocharger to the final vent to open air. Turbo-back systems are generally produced as aftermarketperformance systems for cars with turbochargers. Some turbo-back (and headerback) systems replace stock catalytic converters with others having less flow restriction. With or without catalytic converter Some systems (including in former time all systems) (sometimes nowadays called catless or de-cat) eliminate the catalytic converter. This is illegal in some places if the vehicle is driven on public roads. Cat-back Cat-back (also cat back and catback) refers to the portion of the exhaust system from the outlet of the catalytic converter to the final vent to open air. This generally includes the pipe from the converter to the muffler, the muffler, and the final length of pipe to open air. Cat-back exhaust systems generally use larger diameter pipe than the stock system. Good systems will have mandrel-bent turns that allow the exhaust gases to exit with as little back pressureas possible. The mufflers included in these kits are often glasspacks, to reduce back pressure. If the system is engineered more for show than functionality, it may be tuned to enhance the lower sounds that are lacking from high-RPM low-displacement engines. Tailpipe and exhaust With trucks, sometimes the silencer is crossways under the front of the cab and its tailpipe blows sideways to the offside (right side if driving on the left, left side if driving on the right). The side of a passenger car on which the exhaust exits beneath the rear bumper usually indicates the market for which the vehicle was designed, i.e. Japanese (and some older British) vehicles have exhausts on the right so they are furthest from the curb in countries which drive on the left, while European vehicles have exhausts on the left. The end of the final length of exhaust pipe where it vents to open air, generally the only visible part of the exhaust system part on a vehicle, often ends with just a straight or angled cut, but may include a fancy tip. The tip is sometimes chromed. It is often of larger pipe than the rest of the exhaust system. This produces a final reduction in pressure, and sometimes used to enhance the appearance of the car. In the late 1950s in the United States manufacturers had a fashion in car styling to form the rear bumper with a hole at each end through which the exhaust would pass. Two outlets symbolized V-8 power, and only the most expensive cars (Cadillac, Lincoln, Imperial, Packard) were fitted with this design. One justification for this was that luxury cars in those days had such a long rear overhang that the exhaust pipe scraped the ground when the car traversed ramps. The fashion

disappeared after customers noted that the rear end of the car, being a low-pressure area, collected soot from the exhaust and its acidic content ate into the chrome-plated rear bumper. When a bus, truck or tractor or excavator has a vertical exhaust pipe (called stacks or pipes behind the cab), sometimes the end is curved, or has a hinged cover flap which the gas flow blows out of the way, to try to prevent foreign objects (including droppings from a bird perching on the exhaust pipe when the vehicle is not being used) getting inside the exhaust pipe. In some trucks, when the silencer is front-to-back under the chassis, the end of the tailpipe turns 90° and blows downwards. That protects anyone near a stationary truck from getting a direct blast of the exhaust gas, but often raises dust when the truck is driving on a dry dusty unmade surface such as on a building site. Lake Pipes Lake pipes [2] are a type of after market performance exhaust added by performance enthusiasts, although some cars were fitted with them from the factory. The exhaust is routed from the exhaust manifold and routed along or beside the bottom of the car body beneath the doors. They were usually chrome plated. Usually they also offered a performance boost as they had less back pressure than conventional exhaust, along with less environmental control (no catalytic converter).

LUBRICATION SYSTEM

For the forty years following the first flight of the Wright brothers, airplanes used internal combustion engines to turn propellers to generate thrust. Today, most general aviation or private airplanes are still powered by propellers and internal combustion engines, much like your automobile engine. We will discuss the fundamentals of the internal combustion engine using the Wright brothers' 1903 engine, shown in the figure, as an example. The brothers' design is very simple by today's standards, so it is a good engine for students to study and learn the fundamentals of engines and their operation. On this page we present a computer drawing of the lubrication system of the Wright brothers' 1903 aircraft engine. Mechanical Operation The figure at the top shows the major components of the lubrication system on the Wright 1903 engine. In any internal combustion engine, fuel and oxygen are combined in a combustion process to produce the power to turn the crankshaft of the engine. The combustion generates high pressure exhaust gas which exerts a force on the face of a piston. The piston moves inside a cylinder and is connected to the crankshaft by a rod which transmits the power. There are many moving parts is this power train as shown in this computer animation:

The job of the lubrication system is to distribute oil to the moving parts to reduce friction between surfaces which rub against each other. The lubrication system used by the Wright brothers is quite simple. An oil pump is located on the bottom of the engine, at the left of the figure. The pump is driven by a worm gear off the main exhaust valve cam shaft. The oil is pumped to the top of the engine, at the right, inside a feed line. Small holes in the feed line allow the oil to drip inside the crankcase. In the figure, we have removed the fuel system and peeled back the covering of the crankcase to see inside. The oil drips onto the pistons as they move in the cylinders, lubricating the surface between the piston and cylinder. The oil then runs down inside the crankcase to the main bearings holding the crankshaft. Oil is picked up and splashed onto the bearings to lubricate these surfaces. Along the outside of the bottom of the crankcase is a collection tube which gathers up the used oil andreturns it to the oil pump to be circulated again. Notice that the brothers did not lubricate the valves and rocker assembly for the combustion chambers.

COOLING SYSTEM

Parts of the Cooling System: 1. RADIATOR Cools off the anti-freeze/coolant mixture by allowing air passing through the tube/fin area to dissipate the heat generated by the engine. 2. WATER PUMP Draws the cooled anti-freeze from the radiator and pumps it through the engine block, cylinder head(s), heater core and back to the radiator. 3. FREEZE PLUGS Is actually a steel plug designed to seal holes in the engine block and cylinder head(s) created from the casting process. In freezing weather they may push out if there is not enough antifreeze protection. 4. HEAD GASKET /TIMING COVER GASKET Seals the major parts of the engine. Prevents oil, anti-freeze and cylinder pressure from mixing together. 5. HEATER CORE Provides heat to the interior of the car by using heat removed from the antifreeze and blown in by the blower motor. May cause steam, odor or actual dripping inside the car when it leaks. 6. THERMOSTAT Controls the minimum operating temperature of the engine. The thermostat is closed when the engine is cold in order to speed warm-up and opens when normal operating temperature is reached to allow the anti-freeze / coolant to pass through the radiator. 7. HOSES (Radiator, Heater, By-pass) Connect the other main components of the cooling system. Hose manufacturers recommend replacing every 4 years regardless of appearance because there may be deterioration of the inside of the hose which cannot be seen. 8. FAN CLUTCH

Senses the temperature of the air coming through the radiator and either slips or binds up to pull the required amount of air through the radiator. 9. ELECTRIC COOLING FAN Most front wheel drive cars use this because of the transverse mounted engine. It is turned on by a system of sensors and relays when the engine reaches about 230 F and stays on until the coolant is cooled to about 200 F. 10. Coolant A liquid cooled system uses a mixture of Ethylene Glycol and water as a medium to cool the engine, and transfer its heat to the outside air.

Charging System

The function of the automobile battery is to supply a sufficient amount of electricity to the automobile's electrical components such as the starter motor, headlights and wipers. However, The battery is limited in its capacity and is not capable of providing, On a continuing basis, All the power required by the automobile. It is necessary, Therefore, For the battery to always be fully charged in order for it to supply the necessary amount of electricity at the required time to each of the electrical components. Consequently, The automobile requires a charging system to produce electricity and keep the battery charged. The charging system produced electricity to both re-charge the battery and to supply the electrical components with the amount of electricity required while the automobiles engine is in operation. Most automobiles are equipped with alternating current alternators as they are better than direct current dynamos in terms of electric power generating performance and durability. Since the automobile requires direct current, The alternating current produced by the alternator is rectified (Converted to direct current) just before output.

Basic of Charging System The charging system includes the alternator, voltage regulator which is often a part of the alternator itself), the battery, and the indicator gauge or warning light on the dash (See Alternator, Battery and Voltage Regulator). The charging system's job is to generate enough current to keep the battery fully charged, and to satisfy the demands of the ignition and electrical systems. The voltage regulator senses the demands on the electrical system, and controls alternator output so sufficient current is produced. A loose V-belt, or a defective alternator or voltage regulator can cause the dash warning light to glow red (or the amp gauge to show and steady discharge). If the problem isn't corrected, the battery will run down and eventually go dead. The electrical system in an automobile is said to be a 12 volt system, but this is slightly misleading. The charging system in most cars will generally produce a voltage between 13.5 and

14.4 volts while the engine is running. It has to generate more voltage than the battery's rated voltage to overcome the internal resistance of the battery. This may seem strange, but the current needed to recharge the battery would not flow at all if the charging system's output voltage was the same as the battery voltage. A greater difference of potential (voltage) between the battery's voltage and the alternator's output voltage will provide a faster charging rate. As long as the engine is running, all of the power for the accessories is delivered by the alternator. The battery is actually a load on the charging system. The only time that the battery would supply power with the engine running is when the current capacity of the alternator is exceeded or when engine is at a very low idle. A basic alternator has 2 main electrical components. The rotor and the stator. The rotor is the part of the alternator that is spun by the drive belt. There are a group of electrical field coils mounted on the rotor. The stator is the group of stationary coils that line the perimeter of the inside of the alternator case. When current (supplied by the voltage regulator - to be explained later) is flowing in the rotor's coils, they induce current flow in the stationary coils. The induced current (and voltage) is an AC current. To convert this to DC, the current is passed through a bridge rectifier.

IGNITION SYSTEM The purpose of the ignition system is to light the fuel/air mixture on fire at the right time. Three types of systems have been used in modern times: The Breaker Point System The Electronic System The Computerized System The Distributorless System We will discuss them all, but the one we will deal with in the greatest detail, is the breaker point system. The way they create the high voltage spark is the same in all types of systems, the only thing that differs is the way they are controlled.

All ignition systems have two circuits The Primary Circuit The primary circuit is the low voltage circuit that controls the ignition system. The primary circuit consists of: Battery - provides the power to run the system. Ignition Switch - allows the driver to turn the system on and off. Ballast Resistor - reduces battery voltage from 12 volts to 9 volts. Points - a mechanical switch that acts as the triggering mechanism. Condenser - protects the points from burning out. Primary Coil - produces the magnetic field which creates the high voltage in the secondary coil. Wires - join all the components together.

The Secondary Circuit The secondary circuit is the circuit which converts magnetic induction into high voltage electricity to jump across the spark plug gap, firing the mixture at the right time. The Secondary Circuit consists of: Secondary Coil - the part of the coil that creates the high voltage electricity. Coil Wire - a highly insulated wire, that takes the high voltage from the coil, to the distributor cap. Distributor Cap - a plastic cap which goes on top of the distributor, to hold the high tension wires in the right order. Rotor - spins around on the top of the distributor shaft, and distributes the spark to the right spark plug. Spark Plug Wires - another highly insulated wire that takes the high voltage from the cap to the plugs. Spark Plugs - take the electricity from the wires, and give it an air gap in the combustion chamber to jump across, to light the mixture. How Does The Ignition System Work Anyway? Electrons, supplied by the battery when the engine is starting, or by the alternator when the engine is running, are supplied to the primary circuit at about 12 volts electrical pressure. When the circuit is completed by turning on the ignition switch, and the breaker points are closed, those electrons flow through the primary coil, across the points to ground, and back to the battery again.

When electrons flow through a wire, a magnetic field is built up around the wire. Make the wire into a coil, and the magnetic field increases by the number of loops in the coil. This magnetic field takes a relatively long period of time to build up. It isn't instantaneous. The time the coil is charging up is called coil saturation, and is controlled by the amount of time the breaker points are closed, or "dwell". the longer the points are closed for, the longer the dwell, and the stronger the magnetic field becomes.

The coil is actually named wrong. It shouldn't be called the coil. It should be called the "coilS". The primary coil is the one that builds up the magnetic field. It has a few hundred turns of relatively large wire in it.. The secondary coil has a few thousand turns of small diameter wire in it because it is the one that will make the high voltage, but low current, and fire the spark plugs. So when the points are closed and the ignition switch is turned on, a magnetic field is built up around the coil. When the points are opened by the distributor cam, electrons can no longer flow, so the magnetic field collapses toward the center of the coil at the speed of light. When it collapses, it moves through the secondary coil. Since the secondary coil has so many turns of wire, and the speed of the magnetic field is so high, a great deal of voltage is induced into it. Not all of the electrical energy is actually used though. Voltage only builds up until there is enough to ionize the air in the gap between the positive and ground electrodes of the spark plug. When there is enough voltage the spark plug fires and releases the energy to ground. It will always take between 5,000 (5KV) and 15,000 (15KV) volts to jump across the spark plug gap. If it takes more, there is too much resistance in the plug circuit, or there is too wide a spark plug gap. If it takes less than 5KV to fire the plug, there is a short, caused by a shorted plug wire, too small a spark plug gap, or a fouled plug. The high voltage electricity produced in the secondary coil goes from the coil tower, through the coil high tension wire to the distributor cap, from the center of the cap across the rotor to the outer terminal of the cap, through the spark plug high tension wire to the spark plug, across the plug gap to ground firing the mixture in the combustion chamber. This all takes place at the speed of light. The coil is actually a transformer. It transforms a twelve volts or so, into as much as 45,000 volts. A breaker point ignition system is capable of producing between 20,000 and 30,000 volts of electrical pressure. There is very little actual current flow. Electronic ignition systems were first used as standard equipment in 1975 because of the 50,000 mile emission durability test required by the Environmental Protection Agency. The problem with the old system which had been used for seventy five years, was the points, which started to deteriorate after 1,000 miles, and were totally worn out by 20,000 miles. An electronic ignition system uses a transistor to turn on and off primary power. Transistors are electronic switches

that either work or don't, they don't just deteriorate in use. Electronic systems are capable of producing up to 45,000 volts and much higher amounts of current than the breaker point system. The spark will take place just before Top Dead Center on the compression stroke. Parts of the Primary Circuit Points The points are not anything mysterious. they are simply a mechanical switch that turns on and off the ignition coil. The are opened by the distributor cam, and closed by the point spring. When they are closed, the electricity flows from the battery to the ignition switch on the steering column, to the positive side of the primary coil, and across the points to ground. The only way the electricity can get to ground is across the points, so when the points open, electrons can no longer flow and the magnetic field around the coil collapses. The points are the weak link in an ignition system that includes them. After as little as 1000 miles they have deteriorated significantly, and gone out of adjustment. By 20,000 miles the engine is not likely to run at all. The points must be replaced, and adjusted at the time of a tune-up. They are set by adjusting "dwell, which is the number of degrees of distributor cam rotation the points are closed for. Dwell, coil saturation time, and cam angle are all the same thing.

As you can see in the diagram, the closer the points are to being closed, the longer they stay closed for and therefore the longer Dwell is. To adjust the points, simply hook up a dwell meter to the coil. ( red lead to negative, black to engine ground) Crank the engine with the distributor cap and rotor off, and adjust the fixed contact of the points until the correct dwell reading is obtained.

If there is a range in the dwell specification, adjust the points to the low end of the range because dwell will always increase as the rubbing block wears down. Condenser The sole purpose of the condenser is to protect the points, and keep them from burning out prematurely. The collapsing magnetic field not only collapses through the secondary coil, but also through the primary coil. The collapsing field induces a few hundred volts in the primary coil. These electrons have to go somewhere, they are just trying to get to ground by the easiest means possible. If they were allowed to jump across the points, they would burn them out in as little as 100miles. They see the condenser as an easy way to ground but what it really does is store them for a fraction of a second. Meanwhile the points have opened far enough that the 300 volts or so, can't jump across them. The condenser is just a little can with a strip of tin foil and a strip of waxed paper, rolled together inside a little can. A wire is attached to the roll of tin foil and the waxed paper is there to separate one roll of the foil from the next one. The condenser is merely a storage room for electrons.

Ballast Resistor (or resistor wire) The coil is designed to operate on 9 volts. Battery voltage (12 volts) is reduced to 9 volts by the Ballast Resistor. When the ignition switch is in the "run" position, the coil is powered through the Ballast Resistor feeding it 9 volts; but when the ignition switch is turned to "start", the Ballast Resistor gets by-passed. This feeds full battery voltage to the coil for better starting. The starter motor is drawing battery voltage down to about 10 volts at this time. Battery Don't forget, without a good battery, you don't have a good ignition system. Primary Coil The primary coil has a few hundred turns of relatively large wire. Its positive side is connected to the ballast resistor, and its negative side is connected to the distributor (or the module in an electronic system). The primary coil is the one that builds the magnetic field around it. Parts of the Secondary Circuit All parts of the Secondary circuit are highly insulated to prevent the high voltage electricity from escaping to ground. Secondary coil The secondary coil has a few thousand turns of hair fine wire. It is the coil that the magnetic field moves through to produce the high voltage electricity. Because of the high number of turns of wire, and because of the extremely high speed the magnetic field is moving at, ( the speed of light ) extremely high voltage is produced, but because the current flow is very small, the wire only needs to be small too. The positive side of the secondary coil attaches to the positive primary wire, and the negative side goes to the coil tower where the coil high tension wire plugs in. Rotor The rotor spins around on the top of the distributor shaft and distributes the spark from the center terminal of the cap to each insert around the outside in the firing order. Is snaps onto, or is held by screws, to the top of the distributor shaft, and only goes on one way. The rotor is made of "Bakelite", a type of plastic. Bakelite differs from most plastics in that is is capable of withstanding a fair amount of heat. It is, however, quite brittle, but it does have high dialectic strength or resistance to current flow. During a tune-up, the rotor should be checked for worn electrodes, cracks, and evidence of punctures. These are places where the electricity has burned through the rotor to the distributor shaft.

Distributor Cap The distributor cap is also made of bakelite. It has brass, copper, or aluminum inserts in it to conduct the electricity to and from the rotor and the high tension wires. The cap usually has ribs on the inside to prevent flashover between the terminals. There is one insert in the center for the coil HT wire, and inserts around the outside for the spark plug HT wires. The plug wires are pushed into these terminals in the firing order. Good quality caps have copper or brass inserts and not aluminum. There is arcing between the cap and rotor and that arcing causes oxidation of the inserts. Aluminum oxide is a very effective abrasive and causes wear on the distributor shaft bearings. During the tune-up, the cap should be checked for any wear on the inserts, and evidence of "carbon tracking". These are places where the electricity has made another way to ground, or one of the other terminals in the cap. Both cap and rotor should be checked during a tune-up, but they don't necessarily have to be replaced unless they show wear. High Tension Wires The HT leads are highly insulated to prevent the electricity taking a short circuit to ground. There are usually one plug wire going to each spark plug, and one coil wire going from the coil to the center of the cap, although on GM's High Energy ignition system the coil wire has been eliminated by placing the coil directly on the top of the cap. Ht leads are usually carbon core; very much like a little piece of string impregnated with graphite. There is very rarely an actual conductor made of copper. The insulation makes up a large percentage of the diameter of the wire, and is usually made of silicon in modern wire sets.

During the tune-up the wires should be checked for evidence of burn through, deterioration of the wire, or boots, or any abnormality. The plug wires should be separated from each other, and never bundled together. Bundling the wires causes cross-fire between the plug leads and therefore the spark plugs. The plug wires can be checked on an engine analyzer, or oscilloscope for high or low firing lines. High firing lines indicate open circuits caused by a broken wire or spark plug, or a wide spark plug gap. Low firing lines indicate a short , caused by leakage to ground. This could be a wire laying across an exhaust manifold or the cylinder head. If you don't have an oscilloscope, HT leads can be checked with an ohm-meter. There should be about a thousand ohms of resistance per foot of wire. When pulling plug wires off the spark plugs, twist and pull the boot, don't yank on the wire itself. This will cause the wire to break inside and although it will still work right then, it will give problems down the road as the wire burns back in both directions from the break. Wire sets don't necessarily have to be replaced during a tune-up, but they should always be checked. Spark Plugs The spark plugs are the last remaining part of a modern ignition system that need servicing on a regular basis.

The plugs must have the correct "reach", or length of the threads, diameter, sealing method, and heat range.

The plug on the left requires the use of a seal ring, or gasket to prevent compression leakage past the threads. The plug on the right does not require a gasket. The spark plug must run at the correct temperature. If the plug runs too hot, above 900 degrees Celsius, it will glow red hot, and the fuel mixture will start on fire all by itself, not when the plug fires. This is called pre-ignition, and must be avoided at all costs. If the plug runs too cool, below 450 degrees Celsius, it will foul up with crud because it never cleans itself. High performance and high compression engines have a great deal of heat in the combustion chamber (remember, its the heat that pushes the pistons down) and so don't require any "artificial" heat created by the plug to keep it hot. High performance engines use cold plugs. Low performance, low compression engines don't have a great deal of heat in their combustion chambers and therefore need to keep the plugs hot in another way. They use hot spark plugs.

Note the short heat path in the plug on the left. Remember, the hottest part of the plug is the center electrode. The shorter the distance the heat has to travel to the coolant, the cooler the plug runs. A hot spark plug has a longer insulator nose. Projected nose or extended tip plugs take the whole insulator and move it further out into the combustion chamber. This moves the tip into the swirling gasses in the combustion chamber and the tip keeps cleaner than a normal plug and prevents fouling.

A technician can tell a great deal about the engine he is working on simply by "reading" the spark plugs

Worn plugs, like the one on the right in the drawing above, should be replaced. The spark plug air gap must be set when the plugs are installed. Spark plugs are not normally cleaned and re-gapped anymore. Sand blasting the insulator gives it a rough finish and it fouls up easier than when new.