A 4 wire ignition coil diagram displays primary/secondary windings, power, ground, and spark plug output in modern vehicles.
An ignition coil is a crucial electrical component in a vehicle’s ignition system. It is responsible for transforming the low voltage from the battery (12V) to the very high voltage (20,000V – 30,000V) required to create a spark to ignite the fuel/air mixture in the engine’s cylinders.
The ignition coil operates on the principle of electromagnetic induction – where electricity is generated in a coil of wire when magnetic fields around it change.
In a vehicle, the ignition coil contains two sets of wire windings – primary and secondary coils. The primary winding receives low voltage from the battery/ignition system.
As this current periodically gets interrupted by components like the distributor or ignition module, it creates a changing magnetic field in the coil.
This changing field induces a very high voltage across the secondary winding which gets sent to the spark plugs to ignite the engine.
The ignition coil provides the high energy sparks needed for igniting and running the engine.
Without a properly functioning coil, the engine would not start or run. This makes it an absolutely vital component in any vehicle’s ignition system.
4 Wire vs 3 Wire Ignition Coils
The key differences between 4 wire and 3 wire ignition coils are in their wiring and internal construction.
- 3 wire ignition coils have 3 terminals – one for the 12V power input from the battery, one for the control signal from the ignition module or computer, and one for the high voltage output to the spark plug. Inside they contain only a primary and secondary winding.
- 4 wire ignition coils add a fourth terminal and internal wire that connects to a sensor built inside the ignition coil. This sensor monitors the primary current in the coil and feeds back this signal to the ignition module or computer.
- The fourth wire allows more precise control and timing of the primary current ramp up and collapse. This results in a stronger spark for better combustion and smoother idle.
- The internal sensor also enables advanced diagnostics of the ignition system by the engine computer. Problems like coil failures or wiring issues can be detected and logged by the computer.
- Overall, the 4 wire design provides more accuracy, better performance, and diagnostics capability compared to a basic 3 wire coil. All modern engine management systems use 4 wire coils, while older distributor based ignitions used 3 wire coils.
4 Wire Ignition Coil Components
A 4 wire ignition coil has 4 terminals or prongs that need to be connected:
- Positive terminal – This connects to the positive battery voltage to provide power to the ignition coil. It is usually labeled as + or POS.
- Negative terminal – This connects to the vehicle ground and completes the circuit. It is usually labeled as – or NEG.
- Switched 12V terminal – This terminal receives 12V power from the ignition switch when the key is turned on. This activates the primary windings in the coil. It is usually labeled as IGN or SW.
- Tach terminal – This terminal provides a pulsing signal to the tachometer to indicate engine speed. It receives the voltage spikes induced in the secondary windings by the collapse of the magnetic field in the primary. The tach uses this to calculate rpm. It is usually labeled as TACH.
The positive and negative terminals provide power to the primary windings in the ignition coil. The switched 12V terminal activates the coil when the ignition is turned on.
The tach terminal taps into the secondary voltage pulses to give a signal to the tachometer.
4 Wire Ignition Coil Wiring
Wiring a 4 wire ignition coil properly is critical for the coil to operate correctly. Here’s a step-by-step guide to connecting the 4 wires:
- Locate the ignition coil on top of the engine and identify each of the 4 wires coming out of it. The wires are typically colored as follows:
- Red – This is the positive 12 volt power supply for the ignition coil primary winding. It needs connected to a 12 volt source from the fuse box or ignition switch.
- Black/White – This is the negative ground for the ignition coil primary winding. It needs connected to the engine block or chassis ground.
- Black – This is the hot output wire that provides the high voltage spark from the ignition coil secondary winding to the distributor cap or spark plug wires.
- Orange/Blue – This is the tachometer signal wire that sends a pulsing signal to the tach gauge on the dash to indicate engine speed.
- Use wire crimpers to attach ring terminals to each ignition coil wire if they don’t already have them.
- Locate the corresponding colored wires in the main engine wiring harness. They are typically grouped together in a section dedicated to the ignition system.
- Bolt the red power wire to the positive 12 volt terminal on the fuse block or ignition switch.
- Bolt the black/white ground wire to any grounding point on the engine block or chassis. Make sure the connection is clean and tight.
- Connect the black hot output wire to the center terminal on the distributor cap or the hot terminal on each individual spark plug wire.
- Connect the orange/blue tachometer wire to the appropriate tachometer input terminal, often marked ‘TACH’ in the fuse box.
Following this wiring method ensures proper voltage and grounding for ignition coil operation and allows the coil signal to reach the spark plugs to fire them and create the engine spark.
The tachometer connection enables engine speed monitoring. Taking care with the wiring helps avoid misfires, poor performance, and ignition issues.
Ignition Coil Primary and Secondary Windings
The ignition coil contains two sets of coil windings – the primary and secondary windings.
These play different but complementary roles in generating the high voltage spark for the spark plugs.
The primary winding is made up of a few hundred turns of thick wire. It receives 12 volts from the battery/ignition switch when the ignition is turned on.
As current flows through the primary winding, a magnetic field builds up.
When the ignition module sends a signal to open and close the primary circuit, the magnetic field collapses and causes a high voltage spike in the thousands of volts to be induced in the secondary winding.
The secondary winding has many thousands of turns of thin wire wrapped around the primary winding.
As the magnetic field around the primary winding collapses and builds, the high voltage spike is induced in the secondary.
The high number of turns in the secondary winding transforms the 12 volts from the primary side into the thousands of volts needed for the spark plug. Without this step-up in voltage produced by the coil windings, the spark plugs would not fire.
So in summary, the primary winding receives 12 volts to build up the magnetic field, while the secondary winding transforms this into high voltage for the spark by the magnetic field collapsing and building.
The two windings work together to boost the voltage for the spark plug spark.
Ignition Coil Operation
A 4 wire ignition coil works by using electromagnetic induction to transform the 12 volts from the battery into the thousands of volts required to create a spark to ignite the fuel/air mixture in the engine’s cylinders.
Inside the ignition coil are two sets of windings – the primary and secondary windings.
The primary winding is made up of heavy gauge wire wrapped around an iron core, while the secondary winding uses many more turns of finer wire also wrapped around the same core.
When power flows into the primary winding from the ignition system, it creates a magnetic field in the iron core.
As the current is turned on and off in the primary winding, the magnetic field expands and collapses rapidly.
This changing magnetic field in the core passes through the secondary winding, inducing a high voltage across its ends – often 20,000 volts or more.
This high voltage spike travels out of the ignition coil to the distributor or coil pack, then to the spark plugs where it arcs across the electrodes to ignite the compressed fuel/air mixture.
The spark is precisely timed by the ignition system to coincide with the engine’s compression stroke for maximum power and efficiency.
So in summary, the 4 wire ignition coil transforms the 12 volt current into a momentary high voltage spike by using the principles of electromagnetic induction and timed switching of current in the primary winding.
This is how it provides the all-important spark to run the engine.
Ignition Coil Failure Symptoms
A failing ignition coil can cause several issues with your vehicle’s performance.
Here are some of the most common symptoms that indicate your 4 wire ignition coil may be going bad:
- Misfiring and sputtering engine – If the ignition coil is unable to provide the high voltage needed to spark the plugs, you may experience misfires, especially under load or at higher RPMs. This can cause the engine to run rough or sputter.
- Loss of power – As the coil fails, your engine will start to lose power especially when accelerating or going up hills. The lack of high voltage reduces the combustion efficiency.
- Lower fuel efficiency – Along with less power, a failing coil will also cause a drop in your fuel mileage. Unburnt fuel due to weak sparks will waste gas.
- Difficult starting – Faulty coils will make it harder for your engine to start. You may need to crank the engine longer before it starts.
- Engine stalling – A severely failing coil can completely stop generating adequate spark leading to engine stalls, especially at idle or lower speeds.
- Check engine light – The ECU will detect misfires or voltage issues and trigger the check engine light with coil-related trouble codes like P0300, P0301, etc.
If you notice any of these symptoms, have your 4 wire ignition coil inspected and tested to confirm. Replacing a faulty coil promptly can restore performance and prevent further issues.
Ignition Coil Testing
Testing a 4 wire ignition coil is an important step in diagnosing ignition system issues. Here are the main steps involved:
1. Check Primary Resistance
Use a multimeter to measure the resistance between the coil’s positive and negative terminals with the ignition turned off.
Consult the factory spec, but primary resistance should be around 0.5-2 ohms for most 4 wire coils. A significantly higher reading indicates a bad primary winding.
2. Check Secondary Resistance
Next measure between the positive terminal and the top of the coil tower. Factory specs vary greatly, but secondary resistance typically falls between 6,000-30,000 ohms. A grossly different reading indicates issues with the secondary winding.
3. Check for Continuity
There should be continuity between the positive terminal and all other terminals with the ignition off. If not, there is likely a break in the windings or internal connections.
4. Perform an Output Test
This requires a coil output tester. With the ignition on, clip the tester to the positive terminal and top of the coil tower.
Crank the engine and check that the coil produces a minimum of 7,000-10,000 volts or the factory specified reading. Lower output indicates a weak coil.
5. Swap with a Known Good Coil
If the above tests reveal issues, swap the suspect coil with a known good one. If the problem disappears, confirm you have a faulty coil.
Thoroughly testing a 4 wire ignition coil requires checking windings, output, and confirming operation. This helps pinpoint coil faults and avoid misdiagnosis.
Ignition Coil Replacement
Replacing a 4 wire ignition coil is a relatively straightforward process that can be done in about 30-60 minutes with some basic hand tools. Here is a step-by-step guide:
1. Disconnect the battery
- Locate the battery and disconnect the negative terminal. This is an important safety step as it prevents sparks while working on the ignition system.
2. Remove the coil wiring
- Trace each wire going into the faulty ignition coil and disconnect them. There should be 2 larger primary wires and 2 smaller secondary wires. Remove any wire looms or brackets that may be holding the coil in place.
3. Unbolt the coil
- Use a wrench or socket to loosen and remove the ignition coil retaining bolts. There may be 2-3 bolts depending on the vehicle. Carefully pull the coil out of the mounting bracket.
4. Install the new coil
- Compare the new coil to the old one – they should have the same number of primary and secondary terminals. Insert the new coil into the mounting bracket. Hand tighten the retaining bolts first, then use the wrench/socket to torque them to spec.
5. Reconnect the wiring
- Refer to a wiring schematic as needed to make sure each wire goes to the proper terminal. Snap any wire looms back into place and secure the coil wiring.
6. Reconnect the battery
- Reconnect the negative battery cable once everything is back in place.
7. Test operation
- Start the engine and let it run, checking for any ignition issues or engine codes. The new coil should solve any misfire problems.
And that covers the full ignition coil replacement process! Let me know if you need any clarification or have additional questions.
Conclusion
A 4 wire ignition coil is a common component found in many vehicles with gasoline engines.
Compared to a 3 wire ignition coil, the 4 wire coil has an additional wire that provides voltage to the ignition control module or ignition coil driver.
The major components of a 4 wire ignition coil include the primary and secondary coil windings, core, and housing.
The primary winding receives 12 volts from the ignition switch to generate the magnetic field.
The secondary winding steps up the voltage to thousands of volts to fire the spark plugs.
Wiring a 4 wire ignition coil properly is critical for operation. The power feed wire provides 12 volts to the primary winding.
The 2 signal wires connect to the ignition module which grounds them to turn the coil on and off.
The fourth wire sends the high voltage spark to the distributor or coil packs.
Inside the coil, the primary and secondary windings are wrapped around an iron core. When power flows into the primary, the magnetic field builds up and is discharged to induce a high voltage in the secondary.
This generates the spark for ignition.
Over time, ignition coils can fail due to bad wiring, faulty modules, cracks, moisture damage, and normal wear.
Symptoms of a bad coil include engine misfires, rough idle, loss of power, and failed emissions tests.
Testing coil resistance and using a scope probe can verify if replacement is needed.
Replacing a 4 wire ignition coil involves disconnecting the electrical connectors, removing any mounting bolts, and installing the new coil.
It’s important to use a replacement coil with the same resistance specifications. With a new quality coil properly wired, the engine should run and perform smoothly.
In summary, a 4 wire ignition coil is a crucial component in gasoline engine ignition systems.
Following proper installation and maintenance procedures will help ensure reliable coil operation and engine performance.
