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Motorcycle CDI Ignition System Parts and Functions

CDI system is one type of ignition system that is widely applied to motorcycles. The CDI system uses the discharged voltage from the capacitor to induce an ignition coil.

As discussed before (CDI system working principle), the CDI system is very different from conventional ignition systems such as battery ignition or magneto ignition.

Then what are the components of the CDI system? let's discuss.

6 Parts of CDI Ignition system and function


Why only 6? that's because the design of the CDI system is simpler so it doesn't need a lot of parts.

1. Source of energy (altenator or battery)

The first component is the energy provider, there are two types of components that can be used as energy providers in the CDI system, alternator and battery.

The alternator can generate electrical energy when the engine crankshaft rotates, the electric current generated is AC. While the battery, is a component of storing electrical energy. The battery can deliver electrical energy directly without turn the engine crankshaft. The electric current generated is DC.

From the explanation above we can see that there is a striking difference between the alternator and battery, the alternator produces AC current while the battery produces DC current. That is why there are two types of schemes in the CDI system, namely the AC CDI system (using an alternator) and the DC CDI system (using batteries).

Although the types of currents are different, both types have the same process. In an AC CDI system, the AC current will be converted into DC by a diode in the CDI unit.

2. CDI unit

CDI unit is a unit that contains several electronic components to trigger the induction of the ignition coil.

So, in this system CDI unit has the same function as breaker point on conventional ignition system.

What are the components in a CDI unit?

  • Diode (AC CDI system)
  • Voltage amplifier (DC CDI system)
  • Capacitor
  • SCR


Diodes are electronic components that have function to convert AC current into DC. As explain in the first point, in the AC CDI system the source of electricity is obtained from the alternator. But the alternator produces AC current.

Therefore, the diode acts as a hardware to convert AC current into DC.

While the voltage amplifier is a special component in the DC CDI system which has function to increase the battery voltage from 12 V to 200 V. This is because the capacitor requires around 200 V voltage for charging while the battery voltage is only 12 V.

But why does the AC CDI system not have a voltage amplifier?

The answer, because the voltage generated by the alternator has reached 200 V so it does not require a voltage amplifier.

Capacitor is an electronic component that can store a voltage at a certain capacity and can release the stored voltage simultaneously. In CDI systems, the discharged voltage of the capacitor is used to induce an ignition coil.

We know before that the capacitor has been charged by the electricity provider (alternator / battery) with a voltage of around 200 V. The voltage will be released simultaneously to cause a very large induction.

While the SCR (silicon controlled rectifier) ​​is a component to determine when the capacitor charged and when the capacitor discharged.

The works of SCR is by open the gate from the power source channel directly to the ground. That will make the current from the power source flow directly to ground so that the capacitor can release voltage.

3. Pick up the coil

The pickup coil is a detector to detect ignition timming. The pickup coil consists of a coil placed near the crankshaft. On the crankshaft there is a protrusion that will hit the pickup coil, this protrusion indicates ignition timing.

When the pickup coil hits the cam, the pickup coil will send pulses or electric waves.

The pulse is sent to the SCR to determine the capacitor. So the pulse from the pick up coil becomes the guidance of the SCR to be active.

4. Ignition coil

The ignition coil on the CDI system works when there is a voltage being applied, this is different from a conventional ignition system that utilizes a drop voltage to induce an ignition coil.

So the ignition coil design is slightly different.

In general the ignition coil on the CDI system is the same as the step up transformer, where the secondary primary has a coil of 100 times more than the primary coil. This causes the secondary voltage to be 100 times greater than the primary voltage, so that when the discharged voltage from capacitor is aplied, then the voltage produced by the ignition coil reaches 20,000 V.

5. Ignition switch

Ignition switch is a device to activate and deactivate the CDI system as a whole. Ignition switches are usually controlled by an ID key, each vehicle has a different key channel.

6. Spark plug

The function of the spark plug is to convert 20,000 V electrical energy into an electric spark. the way the spark plug works is actually quite simple, just by providing a gap between the electrode (+) and ground (-).

Automatically, an electric spark will be formed because the voltage of 20,000 V is very large and is able to jump electrons.

How CDI Ignition System Works On Motorcycle? Check This Out

In the previous article we have discussed the magneto ignition system, where this system is used on small gasoline engines such as on motorcycles.

In addition, there is an ignition system on the motorcycle that is more effective than magneto.

That is CDI (capacitor discharge ignition).

Then what is CDI? How does it work ? and what's the difference with the magneto ignition system? let's discuss together.

CDI Ignition System Definition


CDI consists of two main words, namely capacitor and discharge.

So, the CDI system can be interpreted as an ignition system that utilizes discharging current on the capacitor component.

What is capacitor?

Capacitor is an electronic component that can store electric current, and can release (discharge) the stored current spontaneously.

In conventional ignition systems such as magneto or battery ignition systems, the use of capacitors is only to prevent sparking at the breaker point. But on CDI systems, capacitors have a major role.

The release of current on the capacitor serves to induce the ignition coil.

This is the first difference between conventional ignition systems and CDI. In conventional ignition systems, induction of the coil occurs when the primary current is cut off. But on CDI, induction actually occurs by releasing more current to the primary coil coil.

Please note, the discharge current of this capacitor can reach 400 volts so that the output voltage can still be increased up to 20,000 V by an ordinary step up transformer induction.

For more details, see the diagram below


Components marked above
  • Alternator, as a source of electric current
  • Ignition switch
  • CDI Unit, in which there are several components such as capacitors, series of diodes, SCR (silicon controlled rectifier)
  • Pick up coil, to find out ignition timming
  • Step up / ignition coil transformer, used to increase the secondary voltage up to 20 KV.
  • Spark plug


The alternator used in the CDI ignition system can produce AC voltages between 100 - 400 V. This current is used as the basis for the induction process.

Then how is the process going?

1. Electricity generation on the alternator

Starting when the engine crankshaft is rotated, the energy to rotate the crankshaft get from mechanical energy (kick start) or electric (motor starter).

Previously, in the alternator there were two main components, namely the rotor magnet connected to the crankshaft and the stator coil located around the magnet.

Crankshaft rotation will rotate the rotor magnet on the alternator, the result is the stator coil produces AC voltage. The voltage produced by this alternator ranges from 100 V (low RPM) to 400 V (high RPM). This electricity is then used as an energy source for the ignition system.

2. The process of charging the capacitor

In this process, electric voltage from the alternator is flowed into the CDI unit, inside the CDI unit there are several parts such as;

  • Diode, serves to change the AC current into DC
  • Capacitor, as a storage and electric discharge
  • SCR


The voltage from the alternator will be directly sent to the capacitor, but because the current is still in the form of AC (alternate current), it needs to be changed to DC (direct current).

Therefore, before the current enters the capacitor, it will pass through the diode.

After passing the diode, the current is change from AC to DC and is directly used to charge the capacitor.

3. The discharging capacitor process

The capacitor can release a voltage that was previously stored, if there is no current source that hits it.

Therefore, to make the capacitor discharge its voltage, the primary voltage circuit of the capacitor must be disconnected or at least prevent the voltage from passing through the capacitor.

But how ?

For this matter, we are not talking about breaker points anymore, in the CDI system it is strongly influenced by two components namely the pick up coil and the SCR (silicon controlled rectifier).

Pick up coil is a coil that will conduct electric waves when there is a magnetic field passed it. That means, the pickup coil must be equipped with a magnet as a triger. The pickup coil is mounted near the rotor magnet, while a small magnet is connected to the crankshaft where the angle adjusted to the engine's timming.

When the crankshat rotates, this small magnet will rotate and each rotation this magnet will induce pick up coil oncel. When this process occurs, the pickup coil will generate electrical waves which are sent to input 2 on the CDI unit.

Then the electrical wave from the pickup coil is sent to the SCR. The function of the SCR is to activate the path from the alternator directly to ground.

For this SCR to work, a triger is needed. This triger is provided by the coil pick up. When an electric wave from the pickup coil enters the SCR, it will ignite the SCR to active.

As a result, the voltage from the alternator will directly flow to the ground because the nature of the electric current is always flowing to the ground with the smallest resistance.

When the voltage flows to ground, there is no more supply to fill the capactitor and this makes the capacitor also release its voltage.

4. Induction process on ignition coil

In the circuit above, it appears that the capacitor is connected to the primary coil. When the capacitor releases the voltage, there will be massive voltage flow to the primary coil suddenly, the voltage can reach 400 V.

Through induction on the ignition coil, a primary voltage of 400 V can change to 20 KV on the secondary coil. Then the voltage from the secondary coil is connected to the spark plug.

Induction on the ignition coil will occur for a moment because all voltage in the capacitor will be released at one time. That is why, spark on the spark plug is also only for a moment.

To do the induction in the next cycle, the capacitor need to charge back. It do by turned off the SCR so that the voltage from the alternator can flow back to the capacitor and chagrge it.

The SCR will be active and periodically inactive according to the triger of the pickup coil.

As explained above, the SCR will work when there is an electric wave coming from the pick-up coil while the pick-up coil will generate electric waves when a small magnet passes through the pick-up coil. When the magnet is pulled away it will automatically eliminate electric waves and the SCR is deactivated.

How Does Magneto Ignition System Works? Check Article Below

In the previous article, we discussed anything about the battery ignition system, but there is another ignition system that is almost similar. Magneto ignition system, then what is a magneto ignition system? How does it work ?

In general, the battery and magneto ignition systems are the same as conventional because they still use a mechanical breaker point to induce the coil.

But the difference is located in the source of energy.

We know that the battery ignition system has an energy source from the battery, but what about small engines that don't have batteries? Where does the energy source come from for the ignition system?
chain saw use a magneto system

Then the magneto ignition system is the solution, the magneto ignition system does not require an energy source such as a battery because the power source will be generated by the engine itself.

A mini generator is connected to the engine crankshaft, it will produce electricity when the crankshaft rotates.

The excess does not require a battery, so the engine design can be very light, but for performance it is clearly less than a battery ignition system that has a stable voltage.

Therefore, magneto is widely applied to small gas engines such as chain saws, tractors, air pumps, ATVs, speed boats, motor cylcle.

Then How Does the Magneto Ignition System Work?

As always, we first discuss the components.

  • Magneto unit
  • Ignition switch
  • Breaker point
  • Capacitors
  • Spark plug


The most influence part is the magneto unit, this component not only as a provider of electric current but also has functions as an ignition coil, so naturally in this system we do not see ignition coil components such as the battery ignition system.

Magneto is basically a mini generator, which is there is a permanent series of magnets connected to a crankshaft and two coils around the magnets.

How magneto works is also the same as generators in general, when the permanent magnet rotates there will be intersection of the magnetic force lines so as to produce an electric current in the coil around the magnet.

However, there are two coils inside the magneto, namely the primary coil and the secondary coil. The secondary coil has 20,000 turns and is connected to the spark plug while the primary coil has 200 turns and is connected to the breaker point circuit.

The operational order is the magneto ignition system

1. Start when the engine crankshaft is rotated

The energy to turn the crabkshaft is obtained from an external non-electric source such as a crankshaft rotator or on the motorcycle is a kick starter.

When the crankshaft rotates magneto will produce electricity in both coils with a relatively small voltage.

Meanwhile, the ignition system need extremely high voltage. Therefore, there must be an induction process to produce extremely high voltages.

2. Electromagnetic induction to increase the secondary coil voltage

To increase the voltage to 20,000 V, it is necessary to do an induction process between primary and secondary coil in magneto.

The induction process is also the same as a battery ignition coil where the induction will occur when the magnetic field collapsed from the primary coil into the secondary coil.

To make the magnetic field collapse, the current in the primary coil must be cut off suddenly. In charge of deciding the primary coil current is a series of breaker points.

This circuit consists of a breaker contact and a capacitor.

Breaker contact is a connector from the primary coil to the ground, but this contact can be disconnected by a cam that is also connected to the crankshaft. This means that on certain timings (combustion timming) the cam will hit the breaker point and break the primary coil current.

While the capacitor is in charge of absorbing current from the primary coil when the breaker contact is open.

Capacitor is an electronic component that can absorb the current about it, when the breaker contact is still closed, the current from the primary coil goes directly to the ground but when the breaker contact is open, this current will be absorbed into the capacitor.

The main purpose of the capacitor is actually to prevent the spark on the breaker contact, that is because the gap on the breaker contact is so small that the current from the primary coil is still possible to jump.

What are the advantages of the magneto ignition system?

  • Does not require a battery
  • Light-design
  • Components are simpler and fewer


What is the lack of a battery ignition system?

  • Sparks on small spark plugs when engine RPM is low
  • When the engine RPM is high, the spark on the spark plug is also quite large
  • Need more effort to start the engine

How Does Ignition Coil Works? Let's Discusse

Why does the ignition system have an ignition coil? what is its function and how does it work? We have written all the explanations below.

Ignition coil is one of the main components in the ignition system. The function of the coil is to change the battery voltage from 12 V to 25 KV.

Some people assume that ignition coil is only found in traditional ignition systems such as battery ignition systems or magneto ignition systems.

In fact, ignition coil can also be found on cars manufactured today. However, the igniton coil has changed a lot.

In the past, there was only one tubular coil that worked for all spark plugs. But now, there is a single coil or dual coil pack system where an engine does not only have one coil for all but one coil for each spark plugs.

What is the ignition coil function?

Its function is only to increase the ignition voltage.

Why does the ignition voltage have to be increased?

The reason is that in order to create a fire jump on the spark plug the battery voltage must be increased thousands of times. If the voltage is only 12 V then there will not be a stepping flame on the spark plug electrode, because to make electron jumps in an air gap, a large voltage is needed.

How does the ignition coil work?

To understand the working principle of an igniton coil, you need to study the igniton coil diagram below.


Main Ignition coil component

  • Primary winding
  • Secondary winding
  • Iron core


In general, ignition coil works the same as step up transformer. Step up transformer, using the electromagnetic induction method to increase the input voltage.

The way it works, there are two coils. Primary and secondary coils, primary coils are located inside while  the secondary coils located in outer side, so the magnetic field of the primary coils will hit the secondary coils.

If the number of turns of the secondary coil is less, the output voltage will decrease but if the number of turns of the secondary coil is higher then the output voltage will increase.

That is what happens during induction.

But on ignition coil, there is a little difference. In the ignition coil, the secondary coil is located inside the primary coil as illustrated above.

Then how does induction take place?

It turns out that the induction of the ignition coil does not occur when there is a current that passes through the igniton coil but it occur when the current in the ignition coil is cut off.

Primary coil will issue a magnetic field when electrified, this magnetic field will occur in the outer area due to the position of the primary coil in the outside area. When the electric current is cut off, the magnetic field that was previously formed will move very quickly towards the inside before finally disappearing.

The fast and simultaneous movement of the magnetic field will induce secondary coils with stronger results.

As a result, the secondary voltage has increased hundreds of times from 12 V to around 25 KV.

Then what is the function of the iron core in the ignition coil?

Its function is to pull the magnetic field from the primary coil, so that the movement of the magnetic field described above will be focused in very quickly.

The good conductor like iron, will be very effective to maximize the induction in the coil. Without this iron core, it is possible that the induction results could not reach 25 KV.

Battery Ignition System Parts And Functions (Full Explained)

Battery ignition system or some call the conventional ignition system is one of many type of ignition system that is widely applied to used cars. But now, the ignition system has changed to full electronic.

However, the basis of an electronic ignition system comes from a battery ignition system.

Therefore, as car enthusiasts, we must keep learning how the battery ignition system works because it is the basis.

We have discussed the article about battery ignition system in the following link; Easy to understand, Battery ignition system working principle

In this article, we will focus on discussing the components of the battery ignition system and each function.

Battery ignition system components consist of;

  • Battery
  • Ignition switch
  • Ballast resistor
  • Ignition coil
  • Contact breaker
  • Capacitor
  • Distributor
  • Spark plug
  • High voltage wire


1. Battery

As the name suggests, the battery is a main part of the battery ignition system. The function of the battery in this system, is as a power source.

Basically, sparks on spark plugs occur as a result of electron jumps with very high voltages. so the source of energy, is electrical energy derived from vehicle batteries.

Generally for passenger vehicles (MPV, SUV) use 12 V batteries.

2. Ignition switch

Ignition switch is a part to manually activate or deactivate the ignition system of the vehicle.

Called manually because we control it.

In the past, the ignition switch was still in mechanical form using plate connections. To activate it, we need to enter the vehicle key and turn it to the ON position.

But now, there is a keyless technology where we do not need to enter the vehicle key into the ignition switch.

However, that does not mean the car now does not include ignition switches. Ignition switches remain only in a more electric form.

3. Ballast resistor



Is a resistor with a high resistance level, its function is to regulate the current that flow to the ignition coil.

What is the purpose?

In general, there are two objectives, to launch better starting system, and to avoid hot temperatures of ignition coil.

During the starting process, the starter motor requires a large amount of current to turn the engine crankshaft. At the same time, the ignition system is active. If there is no resistor, more electric current will enter the ignition coil than the starter motor.

Because the ignition coil has smaller load than the starter motor load so naturally the electric current will flow more to the smaller load.

To avoid this, a high resistance resistor is placed to limit the amount of current entering the ignition coil, so that the starter motor can work stronger.

In addition to the starting process, the electric current can also affect the ignition coil temperature. Large currents cause high ignition coil temperatures, while high temperatures can reduce electromagnetic induction.

Therefore, the ballast resistor also serves to maintain the ignition coil temperature so that it is not too hot.

4. Ignition coil

Is a step up transformer which function is to increase the voltage. The working principle of the ignition coil is also the same as a transformer that uses two coils with different number of turns.

But the thing that make it different is, the primary coil is located on the outside while the secondary coil is located on the inside.

Then how does electromagnetic induction take place?

It turns out that induction occurs when the electric current in the primary coil is cut off. The process is like this, when the current in the primary coil is still connected, magnetic fields appear around the primary coil. When the primary coil current is suddenly cut off, the magnetic field moves inside before finally disappearing.

When the magnetic field moves rapidly inside of the secondary coil, that's when electromagnetic induction occurs.

The article about ignition coil will be full explained on this article How does ignition coil works ?.

5. contact breaker / breaker point



It is a mechanism to disconnecting and connecting current on the primary coil quickly and precisely.

In this mechanism there are three main components, namely cam breaker, arm breaker and breaker point.

Contact breakers work mechanically, using two contacts. When these two contacts are connected, the primary coil current is also connected. But when these two contacts are separated, the primary coil current is also separated.

The component for separating contact breakers is cam breakers. Cam breaker consists of cam which can bring up the breaker arm. When the breaker arm is raised, the contact will separated. Conversely, when the cam shifts, the contacts are connected again.

6. Capacitor

Serves to prevent splashes in the contact breaker.

Although it is not a main part, capacitors greatly affect the performance of the ignition system. Because when there is a spark on the contact breaker, the primary current is not cut off so there is no induction in the ignition coil.

In fact, the breaker contact gap is so small that a spark could appear even though it is only 12 V.

To prevent this, the capacitor is located after the breaker point and before the ground. Capacitor is an electronic component that is able to store a little electricity and immediately release it when the current source is stop.

When the contact breaker is still connected, the capacitor will store current, when the breaker contact is broken the capacitor will release an electric current (discharge) so there is no potential difference in the two contacts.

That is why there is no spark.

7. Distributor



Is a component for distributing the ignition coil output (secondary coil) to each spark plug with the appropriate firing order.

You can only find distributors on engine that have more than one cylinder such as a car. While for single cylinder engines such as motorcycle, there are no distributors.

8. Spark plug

Spark plugs are components for converting electrical energy into sparks.

How did it happen?

Spark plug uses the air gap principle that utilizes the potential difference between the electrode (+) and ground (-). So when high-voltage electricity reaches the spark plug electrode, the electron automatically jumps to the ground because the higher the voltage, the higher the potential difference.

The higher the potential difference, the stronger the electron's movement.

Actually the electron jump is not a fire, but just a flash of electricity. but also has a burning effect, so it can be used for combustion.

9. High voltage wire

It is a special cable used to carry 20,000 V electrical energy from the ignition coil to the spark plug.

The diameter of this cable is quite large, sometimes when we touch the cable insulator, we can be electrocuted even though not dangerous. That shows how high the voltage of this spark plug wire.

Battery Ignition System Working Principle and Parts Explanation

Nowadays the battery ignition system is rarely found, besides the old-typed ignition system is also considered less efficient.

But the electronic ignition system that is widely applied now is the result of the development of the battery ignition system. So we also have to learn how the battery ignition system work, because it is the basis of the car ignition system in the current era.

If you are looking for a complete explanation of the battery ignition system, you are lucky because in this article we will discuss it in detail but easy to understand.

Battery Ignition System Definition


A battery ignition system is an ignition system that uses batteries as the main energy. We know that the function of ignition system is to run combustion inside the engine, to do that, the system is need to provide a spark.

Sparks are obtained from changes in electrical energy, so the spark plug actually comes from electricity in the battery.

Then how can a 12 volt DC battery comes into a spark on a spark plug?

Simply put, this spark arises due to the very high voltage on the spark plug. While in high voltage electricity, the power is also very high so that we can see the sparking electrons on the spark plug gap that only 0.8 mm.

More details will be explained below.

Battery Ignition System Parts and Function

There are several main components in the battery ignition system, among others;

Battery, it is a source of energy for the ignition system.
Ignition switch, to activate or deactivate the ignition system manually (via ignition key).
Ignition coil, is a step up transformer to increase the battery voltage.
Contact breaker, is a mechanism to cut the primary winding of the ignition coil so that the voltage on the secondary winding can rise significantly.
Capacitor, an electronic component to prevent electrical sparks in the contact breaker.
Distributor, used to divide the secondary winding from the ignition coil to each spark plug, you can only see the distributor on car engine (more than 1-cylinder engine)
Spark plug, is an actuator that can convert high-voltage electrical energy into sparks.
High voltage wire, there are two types of wires in the ignition system namely standard cable (12 V) and high voltage cable with a larger diameter to be able to conduct electricity with voltages up to 20 KV.

Battery Ignition System Working Principle

To understand how the battery ignition system works, you need to understand two main parts. Namely;

Ignition coil and contact breaker.

As explained above, the ignition coil is a step up transformer that can increase the voltage. But the ignition coil design is not like a transformer in general.

Here, the primary winding is located on the outside while the secondary winding is located inside the primary winding.


Then how the ignition coil is able to increase the voltage of 12 volts to 20 KV?

The answer is because of the magnetic field, secondary winding has a greater number of turns so that the output voltage is greater than the input voltage. But why does it reach 20 KV?

That is because the primary coil magnetic field is not static but moves from outside to inside, to move the magnetic field of primary winding, the current in the primary winding must be cut suddenly.

When the current still flows in the primary winding, a magnetic field is formed on the outside of the ignition coil. When the current in the primary winding is cut off, the previously formed magnetic field will move inward towards the secondary winding before finally disappearing.

The induction will suddenly increase the secondary winding voltage so that it can be converted into sparks.

This is where the contact breaker job, this serves to cut off the primary current according to ignition timming.

After understanding how the ignition coil works, you can see the diagram below.


From the diagram above, there are two schemes

1. Primary schema

As explained above, this primary scheme serves to induce the ignition coil. This scheme, if written down, starts from the battery - ignition switch - primary winding of ignition coil - contact breaker - capacitor - ground.

2. Secondary scheme

The secondary scheme is a series to pass high voltage electricity to the spark plugs to create sparks.

This is from the battery - ignition switch - secondary winding of ignition coil - distributor - spark plug - ground.

How can the contact breaker cut off the primary current according to engine ignition timming?

 It just about the mechanism, we know there is a valve mechanism where the engine valves are always open and closed at the right time. That's because there is a connection between the crankshaft and camshaft.

The contact breaker mechanism consists of a cam breaker, and a breaker lever.

Cam breaker is connected to the camshaft which is also indirectly connected to the crankshaft. When the cam touches the breaker lever, the contact point will be raised and that causes the primary current to be cut off.

Meanwhile, when the cam shifts, the contact point is back attached so that the primary current is re-connected.

Cam is designed to always touch the breaker lever when the piston is at TDC at the combustion step. So that induction also only occurs in ignition timming.

The engine RPM is directly proportional to the ignition interval because the higher the engine RPM, the faster the cam breaker rotates and it causes the faster induction interval.

Fuel Injection Pump Working Principle in Diesel Engine

There are two types of injection pumps on conventional diesel engines, inline pump and distributor pump.

We have discussed the difference between the two types of pumps in the previous article, you can access these 3 types of fuel injection pump in diesel engines.

in this article, we will discuss in detail about the inline injection pump.

How does it work ? what are the components? we will discuss it all.

Definition of Inline Injection Pump


Inline injection pump is a high pressure pump on a diesel engine that is used to increase diesel fuel pressure up to 18,000 PSI individually.

That is, each injector will be served by a plunger unit.

It can be said, in a 4 cylinder diesel engine there are 4 injectors and 4 plungers.

The main characteristic of the inline injection pump, lies in the configuration of each plunger. Each plunger is placed in line above a camshaft pump.

That's where the name inline pump is taken. In addition to being called an inline pump, this type is also known as the individual pump because, as explained above, this type uses one plunger for each cylinder.

The main component of the inline injection pump

There are 5 main components in the inline injection pump,


  • Camshaft pump
  • Plunger
  • Fuel barrel
  • Fuel feed
  • Rack and pinion


The camshaft pump is used to drive the plunger in order to press the fuel. While the fuel barrel, is the place to hold fuel that will be pressed to the injector.

This is the configuration, the plunger is located above the camshaft and the fuel barrel is located above the plunger.

Rack and pinion is a mechanism to regulate the amount of fuel in the fuel barrel. This mechanism will regulate the diesel engine RPM.

Fuel feeds are fuel enter-exit door, there are three fuel feeds
inlet feed, used as fuel entrance from the tank to the pump
output feed, used as the fuel exit to the injector in high pressure conditions
return feed, used to drain the remaining fuel that is not pressed into the injector

And how does it work?

1. The outside mechanism of injection pump

Generally, there is a mini pump that is used to transfer fuel from the tank into the injection pump. This pump works mechanically, meaning it is driven by the crankshaft engine.

So, to run the fuel flow we need to crank the engine.

When the crankshaft rotates, the mini pump will send diesel fuel from the tank into the injection pump through the inlet feed. From the inlet feed, the fuel directly fill the fuel barrel and it is ready to be pressed.

2. The injection pump mechanism

The pump camshaft is connected to the engine crankshaft, so that when the engine cranks automatically the pump camshaft rotates.


This rotation will move the plunger, so that the plunger is pressed upwards and as a result the fuel that is already in the fuel barrel is pressed with high pressure and enters the injector.

When the cam has finished pressing the plunger, the plunger returns to the bottom position. This will reopen the fuel barrel chamber, so that the fuel from the inlet feed filling the fuel barrel directly.

3. Engine RPM setting mechanism


To adjust engine RPM on conventional diesel, it is done by adjusting the amount of fuel injected by the injector.

In this case, the control is located in the fuel barrel. How much the amount of fuel in the fuel barrel when it is pressed will affect the engine RPM.

it is the task of rack and pinion. These two components will regulate the amount of fuel in the fuel barrel by regulating fuel disposal through the return feed.

The amount of fule is less (Low RPM)

The amount of fuel is more (high RPM)

So, there is a fuel path inte plunger from the fuel barrel leading to the return feed.

This path is made with a certain slope, so that when the angle of the plunger is rotated, it will affect the amount of fuel contained in the fuel barrel

To be clearer you can see the picture (viewed from side)

a. when low RPM

The amount of pressed fuel is lower, so the angle of plunger can be seen from the picture.


2. when high RPM

The amount of pressed fuel is more, so the angle of plunger can be seen from the picture.


3 Type of Fuel Injection Pump With Definition and Differents

We know that the diesel engine is a self-ignition engine, that means the combustion is occur by itself.

However, combustion in diesel engines does not appear immediately but there are several trigers that cause combustion to occur. At least there must be two things, first high pressure air with a temperature greater than the flash point of the diesel fuel.

second, the fuel is atomize (pulverize) in the high pressure air. If the two trigers are fulfilled, then combustion will occur spontaneously.

To get atomize fuel, a fuel mechanism is needed. The mechanism will force fuel out of the narrow gap with high pressure. To increase the pressure of diesel fuel, we know a component called an injection pump.

Then, how many types of injection pumps are used in diesel engines? we will discuss in detail.

3 Types of Diesel Fuel Pumps


Maybe you only know there are only two types of injection pumps in diesel engines. But if we see further, there is one type that is actually applied to many recent vehicles.

1. Individual inline pump


An individual pump is a pump mechanism with an individual fuel delivery system. That means that each injector will be served by a plunger mechanism.

It can be say, the number of plungers is the same as the number of injectors.

However, all the plungers are placed together in one pump unit in a line position. That is what causes this pump also called the inline injection pump.

The main components of this type of pump, among others;

  • Camshaft with the number of cam according to the number of plungers
  • plunger which functions to increase fuel pressure
  • Fuel barrel, a small space where the fuel is ready to be sent to the injector.


The way it works, when the crankshafy rotates, the camshaft pump also rotates. The rotation of the camshaft will cause the cam to press against the plunger alternately.

When the plunger is pressed against the cam, the fuel pressure rises immediately so that the fuel is sprayed from the injector.

2. Distributor pump type


Distrubutor pump is a type of injection pump with smaller design. The main purpose of the distributor pump, as a solution for vehicles with limited space.

The main feature of the distributor pump is the injection system. The inline type uses one plunger for one injector, but the distributor type uses a single plunger for all injectors.

The way it works, this plunger will press all the fuel in each fuel barrel alternately. The fuel barrel is placed around the pump shaft.

When the pump shaft rotates, the plunger will press the fuel in the fuel barrel alternately according to the ignition timing.

Even though it has a smaller design, the distributor pump does not have high fuel pressure. Therefore, this type is rarely used for high capacity diesel engines.

3. Continuous pump


Continuous pump is the latest type of diesel injection pump. As I said earlier, this type is actually the most widely applied today.

Continuous pump is an injection pump that is applied to the common direct injection system.

Judging from the physical, this pump has the smallest form of all types that we discuss. The reason is this pump only has a single function.

Its function is only to increase fuel pressure stably at high pressure. The pressure generated is also very high (30,000 - 40,000 PSI)

While the two types above, in addition to increase fuel pressure also regulates the timing and volume of sprayed fuel. So it's reasonable that the form is quite concise.

The way this pump works is like a water pump that uses a turbine even though some types also use membranes. The pump will suppress the fuel and hold the fuel pressure at the applied limit.

How is the fuel spraying technical?

On the common rail system, to spray the fuel is regulated by the injector directly with the ECU command. So, the pump duty only ensures maximum fuel pressure so that once the ECU opens the injector, fuel can be atomized.