Ignition timing is essential to engine performance.
It controls when the spark plug fires during the compression stroke.
But what is ignition timing?
What does it have to do with your engine making that knocking sound?
We’ll address both those questions in this article. We’ll look at signs your ignition timing is off, and the difference between ignition advance and ignition retard. We’ll also cover how ignition timing is controlled, and some ignition system faqs.
This Article Contains:
- What Is Ignition Timing?
- Signs Your Ignition Timing Is Off
- Ignition Advance VS Ignition Retard: What’s the Difference?
- How Is Ignition Timing Controlled?
- 5 Ignition System FAQs
Let’s begin.
What Is Ignition Timing?
Ignition, or spark timing, controls the firing of your spark plug during the compression stroke. Proper ignition timing is essential to ensuring that your engine functions at peak efficiency.
Want to know where ignition timing applies?
Here’s How a Four Stroke Engine Works:
Each ignition cycle has four strokes — two up and two down, creating two crankshaft revolutions.
1. Intake Stroke — Down
This stroke goes down and draws in the air-fuel mixture.
2. Compression Stroke — Up
Here, the piston moves up, maximizing air compression at the top of the stroke.
This is where ignition timing does its work.
The spark plug is set to fire a few milliseconds before the piston reaches the top of its stroke. It does this because fuel takes a finite — although short — time for its explosive flame to propagate.
The fuel needs to explode with maximum power, so the spark must arrive slightly before the piston reaches the top for this to happen.
When the air-fuel mixture in the combustion chamber ignites, pressure is built in the cylinder as the burning gasses expand. Then pressure maximizes just as the piston hits top dead center (TDC).
3. Power Stroke — Down
Once spark ignition occurs, the explosive pressure drives the piston down as hard as possible.
4. Exhaust Stroke — Up
As the piston moves up, the exhaust gas is driven from the cylinder, ready for the whole process to start again.
The spark’s timing is crucial to maintaining high engine performance. However, a range of factors can influence your engine’s ignition timing:
- The spark plugs’ condition
- The engine’s temperature
- The intake pressure
Any changes or upgrades to your engine will also require an ignition timing adjustment, as you can take on engine damage if your spark plug timing is off during the compression stroke.
Now that you have the gist of ignition timing, let’s discover how to tell if your ignition timing is off.
Signs Your Ignition Timing Is Off
Several performance issues can occur if the timing of your ignition system is awry.
Here’s what to watch for:
A. Engine Knocking
If your ignition spark occurs at a position too advanced to the piston position, the rapidly combusting air-fuel mixture can push against the piston, which is still moving up during the compression stroke. In severe cases, the advanced ignition spark results in engine knocking and is known as pre ignition or detonation.
Engine knocking can also happen when combustion occurs inside the cylinder after the spark plug fires.
B. Decreased Fuel Economy
The ignition spark’s timing is essential because if it’s delayed or too fast, the entire combustion process is off. Your engine will compensate for the reduced power by using more fuel and reducing fuel economy.
C. Overheating
If the air and fuel mixture is ignited too soon during combustion, the heat generated will increase and damage different engine parts.
D. Low Power
If the spark occurs too late to the piston position, maximum cylinder pressure will happen after the cylinder reaches peak cylinder pressure. Missing the window for peak cylinder pressure results in lost power, high emissions, and unburned fuel.
Always take note of the above symptoms to catch problems with your ignition timing early.
Want to know the difference between ignition advance and retard?
Let’s discuss this.
Ignition Advance VS Ignition Retard: What’s the Difference?
You measure ignition timing by noting the degrees of a crankshaft rotation before top dead center (BTDC). Spark plugs need to fire on time, and this can be achieved by advancing or retarding the timing of the engine.
1. Timing Advance
Timing advance means your spark plugs fire earlier in the compression stroke, farther from Top Dead Center (TDC). Advance is required because the air-fuel mixture in the combustion chamber doesn’t burn immediately, and it takes time for the flame (spark plug fire) to ignite the mixture.
Advancing the timing of your ignition increases your engine’s horsepower and helps raise high-end power and reduce the low end. The advance helps get the spark past the ignition delay.
What about the ignition advance angle?
The ignition advance angle is when the crankshaft’s crank doesn’t reach the top dead center when a spark appears between the spark plug’s electrodes.
2. Retard Timing
Retard ignition timing causes your spark plug to fire later in the compression stroke. Retarding ignition timing reduces engine detonation, i.e., combustion inside the cylinders after the spark plug fires.
Engines running at higher pressure levels, like turbocharged or supercharged engines, benefit from retarding the timing of an engine. Retard timing on these engines helps compensate for denser air-fuel mixtures, allowing them to run better.
Let’s move on to discover how proper ignition timing is controlled.
How Is Ignition Timing Controlled?
In most modern engines, the computer handles ignition timing control.
However, engines with a distributor can deal with ignition timing control in many ways:
A. Mechanical Advance
With mechanical advance, as engine rpm increase, it uses centrifugal force to push weights outward. The weight’s movement rotates the trigger mechanism, which causes the ignition to be triggered sooner.
B. Vacuum Timing Advance
With vacuum advance, as the engine vacuum rises, it pulls the diaphragm inside your vacuum canister. Since the diaphragm is connected to the advance plate by a linkage, its movement rotates the trigger mechanism. The vacuum timing advance causes the ignition to be triggered early.
C. Computer-Controlled Compatible Distributors
Here, an external computer (or ECU) controls the timing and the ignition coil. The distributor sends an alert from its internal pickup module to the ECU. The ECU can also get its signals from engine sensors like the camshaft or crankshaft sensor.
The ECU sends a signal to the coil, telling it to fire. Current travels from the coil to the distributor cap and rotor, and a spark is routed to the spark plug.
Let’s answer some ignition system FAQs.
5 Ignition System FAQs
Here are the answers to a few questions regarding ignition systems:
1. What Is Engine Timing?
Two kinds of engine timing take place in every engine. There’s camshaft timing (valve timing) and ignition timing (spark timing).
Cam timing manages valve opening and closing. Ignition timing manages when the spark plug fires. These different actions need to be timed together to make the engine work.
2. What Is Initial Timing?
Initial timing is the amount of ignition timing applied to the engine at idle and is set by the position of the bolted-down distributor.
3. What Is Static Timing?
It’s a method for setting your ignition timing and occurs when you set your ignition timing with your engine off.
Here’s how:
You set the crankshaft at the correct number of degrees before TDC, then adjust the distributor by turning it till the contact-breaker points are opening slightly.
The amount of total timing required determines the initial timing. The proper setting will also depend on the amount of mechanical advance your distributor provides.
However, this timing method doesn’t consider wear between two parts, such as the teeth of gears.
4. Are There Different Types of Ignition Systems?
Yes. We’ll be discussing two ignition systems:
A. Mechanical Ignition Systems
This ignition system uses a mechanical spark distributor to carry a high-voltage current to the correct spark plug on time.
When setting an initial timing advance or retard, the engine should be idle, and the distributor should be adjusted to achieve the best ignition timing for the engine at idle speed.
B. Electronic Ignition Systems
Newer engines typically use computerized ignition systems (electronic ignition). The computer has a timing map containing spark advance values for every engine speed and engine load combination.
Note: The engine speed and engine load will determine how much total advance is needed.
The computer signals the ignition coil to fire the spark plug at the indicated time. The majority of computers from original equipment manufacturers (OEM) can’t be modified, so you can’t change the timing advance curve.
5. How Do Mechanics Adjust Ignition Spark Timing?
Your mechanic will need a timing light to get started with this job. When the engine is running, a timing light illuminates each timing mark on your crankshaft pulley or flywheel.
What they’ll do is:
1. Locate the timing mark on your crank pulley — as with most cars or modern engines — or flywheel.
2. Identify a stationary notch indicating the current base timing as the engine operates.
3. Refer to your vehicle manual to check the correct spark plug gap and the idle speed to adjust the base ignition timing properly.
4. Start the engine and engage your parking brake, then let it idle for about 15 minutes to bring it to normal operating temperature.
5. Turn off the engine and disable computer-controlled advance.
6. Connect the timing light. Keep the timing light leads away from spinning engine components like fans and belts to avoid engine damage.
7. If you have a distributor with a vacuum advance, ensure the hose is disconnected and plugged.
8. Start and let the engine idle.
9. Shine the timing light on the timing marks on your crankshaft pulley, and as the light pulses, they’ll see the stationary line pointing to the current degree mark. They’ll then adjust the timing base accordingly.
10. Turn off the engine and put everything back in its place.
Wrapping Up
The ignition timing process is intricate; having one component out of the loop could spell disaster. To avoid setbacks and ensure your vehicle is always in working condition, regularly have your car serviced by professionals like AutoNation Mobile Service.
AutoNation Mobile Service is a professional mobile mechanic service available to come straight to your driveway.
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