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The automotive ignition system has two circuits a low-voltage primary circuit and a high-voltage secondary circuit.
An oscilloscope displays voltage changes within a certain period, and the oscilloscope would be the best tool to display the voltage.
Oscilloscope works on the principle of displaying voltage over a period of time on the screen.
Voltage traces are displayed as a graph of voltage on a horizontal axis over a period of time.
Oscilloscope works on the principle of displaying voltage over a period of time on the screen.
Voltage traces are displayed as a graph of voltage vertically over a period of time horizontally.
The vertical scale on the screen represents voltage and the horizontal scale indicates time.
Primary circuits are measured in volts, and secondary circuits in kilovolts, or thousands of volts.
Time is measured in the percentage of one complete engine cycle or milliseconds, thousandths of a second.
The ignition system voltage trace primary and secondary is divided into three sections
When looking at the patterns, you are looking for something that doesn't look normal compared to the other cylinders.
An abnormal pattern would indicate a problem in that particular cylinder.
Each pattern is best used to identify a particular malfunction.
There are usually three patterns:
Parade or Display Pattern
Raster or Stack Pattern
Superimposed pattern
A superimposed pattern of voltage traces for all cylinders is displayed on top of each other.
This pattern is a quick look at the ignition system operation and can also reveal certain problems
The parade or display pattern displays voltage traces for all cylinders one after another across the screen from left to right in the firing order. This procedure allows the comparison of voltage levels between cylinders.
The parade pattern display is helpful in diagnosing problems in the secondary circuit.
The raster parade pattern displays the voltage traces for all cylinders stacked one above another in the firing order. This display allows you to compare the periods of the three sections of a voltage trace
The parade or display pattern displays voltage traces for all cylinders one after another across the screen from left to right in the firing order.
This procedure allows the comparison of voltage levels between cylinders.
The parade pattern display is useful for diagnosing problems in the secondary circuit.
The same ignition coil will fire each pair of cylinders. One cylinder will fire on the compression stroke "event" and the companion cylinder will fire at Top Dead Center on the exhaust stroke also known as "waste spark".
Resistance determines the voltage requirements for each cylinder. The Top Dead Center Compression cylinder will have higher resistance, which requires a higher voltage to ionize the spark plug gap, than its companion cylinder on TDC exhaust.
High resistance is caused by the Air Fuel Ratio "rich or lean" and high pressures within the cylinder on Top Dead Center Compression. The cylinder on top dead center exhaust will have inert gases and very low pressure requiring much less voltage to ionize the spark plug gap.
While in the parade pattern and looking for an abnormal signal, you are comparing one signal to another. For example, when looking for an oil-fouled plug, you may see a lower-than-normal fire line or longer-than-normal sparkline with no activity.
Using the different displays on the oscilloscope makes it easier to view certain sections of the ignition patterns
Example:
The display pattern makes it easier to see the firing line when looking for an open wire or high resistance in the circuit.
The raster pattern makes it easier to see the spark line checking for a fouled plug.
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