The injectors are one of, if not the most important part of an internal combustion engine. It is basically a switching electromagnet that controls a tapered valve seat. Opening and closing in milliseconds according to a duty cycle signal sent by the ECU, allowing high pressurised amounts of fuel to be precisely injected into the manifold or combustion chamber.
As the throttle is opened, the ECU tells the injectors to stay open for longer and close for shorter periods at a time. It is usually explained as a percentage, where at wide open throttle the injector may be open around 80 to 90% and closed 10 to 20% of each cycle. At idle the injectors may only open 10 to 20% and closed the other 80 to 90% of the time in each cycle.
The ECU collects alot of data feedback from the engines sensors and the injection cycle is determined by this various, ever changing information. That is why it is important to have sensors that are operating effectively.
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| An Injector Pattern |
Here is an example of an injector operating correctly. And as you can see the voltage spikes high, quickly (about 60v) and then slowly returns to a normal voltage. This happens within about 4 milliseconds.
Injectors are most accurately tested off the vehicle. They are benched tested in order to visually examine the spray pattern, delivery volume or leakage (dribbling). Sometimes even possible seal damage.
Ignition System
Ignition systems are another key component in an internal combustion engine. They create a spark at the desired time the ECU signals and intends combustion of the air/fuel mixture.
Components often include a power source, an ignition switch, coil or coil pack, an igniter module, a trigger generating component/distributor, distributor cap, rotor, HT leads and spark plugs. A newer, more commonly used setup will contain a direct ignition coil. This does away with most of the components previously used such as HT leads, distributor/distributor cap, rotor and in some cases the igniter module as well.
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| A Basic Ignition System |
Testing Ignition Coils
Older ignition coils were very basic where they had two sets of windings.The secondary winding is constructed of thin wire wound tightly around the iron core, located in the center of the coil. The primary winding is constructed of thick wire and is wound around the outside of the secondary windings.
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| A Single Coil Cross-section |
Low voltage is coming through the positive terminal attached to the primary windings and is earthed out the negative terminal on the coil housing. When switching occurs in the primary triggering circuit and over the primary winding, the voltage built up in secondary windings collapses and creates a giant energy surge over the spark plug gap.
Testing coils using an ohmmeter off the vehicle is a reliable way of retrieving knowledge of their condition.
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| Testing the Primary Winding |
When testing primary windings the ohmmeter must be connected between the positive and negative terminals on the coil housing.
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| Testing the Secondary Winding |
When testing the secondary windings, the ohmmeter must be connected to both the positive terminal on the coil housing and the negative side of the secondary windings. Being where the HT lead conducts the power to the distributor cap.
The readings against the specifications as follows (two separate coils are being tested):
Spec: Coil #1 No.CIT-118 Voltage - 12v
Primary - 1.0-1.3ohm Secondary - 8.5-9.5k/ohm
Spec: Coil #2 No.CIC-31 Voltage - 12v
Primary - 3-4ohm Secondary - 7-8k/ohm
Results are:
Coil #1 Primary - 2ohm Secondary - 9.38k/ohm
Coil #2 Primary - 3.9ohm Secondary - 8.46k/ohm
Resistance through the primary windings is a little high, but other than that these coils will perform as normal.
Wasted spark type coil packs can be tested using a multimeter also as follows (one individual wasted spark type coil pack is being tested)(four cylinder type):
Coil #1 Primary - 1.1ohm Secondary - 6.95k/ohm
Coil #2 Primary - 1.1ohm Secondary - 7.13k/ohm
Ballast resistors (used more commonly with 9v coils) can also be tested, as follows:
Spec: Ballast #1 No.BR1 0.9 - 1.1ohm
Spec: Ballast #2 No.BR3 1.5 - 1.7ohm
Results are:
Ballast #1 No.BR1 2.2ohm
Ballast #2 No.BR3 2.4ohm
Results are a bit high, this wont cause damage to any other components. Although it may affect the performance of the ignition system.
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| Testing the Current and Voltage Drops |
Current can be tested in a circuit. Here we test a coil and a ballast resistor in series. As you can see the multimeter needs to be in the circuit. So the multimeter is connected between the positive terminal at the power source and the entry terminal of the ballast resistor.
We can now collect the current value of the circuit. Then disconnect the multimeter and collect voltage drop values over the coils primary windings and the ballast resistor. As follows:
Current in the circuit: 1.9A
Coil (CIC-31) calculated Voltage drop: A x R = V
= 1.9A x 3.9ohm
= 7.41v
Coil measured Voltage drop: 7.59v
Ballast (BR3) calculated Voltage drop: A x R = V
= 1.9A x 2.4ohm
= 4.56
Ballast measured Voltage drop: 3.55v
Types of Ignition Systems
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| Basic Single Coil Schematic |
Here we have the original, more basic type of ignition system. It consists of the typical components found in a basic ignition system. A 12v power supply, a 12v coil (no ballast resistor in necessary), an igniter module, an HT lead and a spark plug. A distributor is not used, as a function generator which takes its place here can produce alot more variety of signals. It can also change signal speed alot more effectively. This makes it alot more accurate in this demonstration than any distributor could be.
This link shows the above single coil circuit in action. It also has an oscilloscope hooked up showing the triggering pattern in the primary circuit:
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| Wasted Spark System Schematic |
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| Wasted Spark wired up |
In this picture above, we have a wasted spark type ignition system. This is a good upgrade from the single coil ignition system. The coils in this system don't have to work as hard as a single coil on its own. This also allows the secondary windings dwell time to stay at an effective time right throughout the increasing engine rpm.
Links involving the wasted spark show the system in action:
Each coil is only igniting two spark plugs. They are in fact ignited simultaneously. One spark plug is ignited on the combustion stroke as normal. But the opposing spark plug is ignited at the opposing stroke which is effectively, the exhaust stroke. In a way this is good because it will ignite any unburnt fuel leaving the combustion chamber and in turn slightly reduce emissions.
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| The Smart Direct Ignition Individual Coil System |
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| Direct Ignition System wired up |
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