Lesson Plan Industry Sector
Transportation

## Ingredient 3: Ignition (updated) by Thomas Dougherty

### Lesson Plan Overview / Details

Upon completion of this session, students will have an understanding of how a primary ignition signal is generated and be able to diagnose the lack of a primary ignition signal using a voltmeter and an oscilloscope.  They will also understand how an ignition coil functions and be able to diagnose a failed ignition coil using an ohm meter and an ignition scope.

### Lesson Time

Primary ignition
2 Hours
Secondary ignition
1 Hour

### Objectives and Goals

• Students will understand how a primary ignition signal is generated and how an ignition coil functions.
• Students will learn how to use a volt meter, ohm meter and oscilloscope and will be able to diagnose ignition system failures using these tools.

### Activities in this Lesson

• It's A Magnet! Hooks / Set

Upon entering the classroom, students will see, "If it doesn't produce heat or light, it's a magnet" written on the board.  There will be various nuts, bolts, washers and permanent magnets on the tables along with some early Chrysler electronic distributors.

• I will briefly explain that anything in an automotive electrical system that does not produce heat or light is a magnet.  We must find a way to use that magnetic field to turn the ignition coil on and off at the appropriate time.

As we cannot see a magnetic field or electron flow through a wire, we will be using a voltmeter and an oscilloscope to draw us a picture.  The voltmeter will show us the quantity of electricity being generated and the oscilloscope will draw the picture.

I will then explain that when a magnet is passed over a coil of wire, the magnetic field stimulates electron flow through the coil and produces AC voltage. I then project a Vantage Pro display on my classroom screen and produce a signal with a Chrysler distributor.  I use a Chrysler distributor as the pickup coil is visible and very similar to what we will be building in class.  I explain amplitude (voltage) and frequency (time).

Students can then play with their volt meters and the remaining distributors to produce a signal of varying amplitude and frequency depending upon how fast the distributor shaft is rotated.

• Build It! Demo / Modeling

Each student selects a nut, bolt and two washers, and is given a length of single strand insulated copper wire.  They are instructed to assemble the nuts and washers on the bolt and wind the wire around the bolt between the washers counting the revolutions as they do.  We then connect the ends of the coil wires to both volt meters and the oscilloscope and pass a permanent magnet across the coil.  Students can witness voltage being generated and view an AC wave form on the scope.  Students will notice the correlation between the length of wire in the coil and the amount of voltage generated.  They will also witness the voltage fall off as the permanent magnet gets further away from the coil and the magnetic field collapses.

• In the secondary ignition section, we will discuss the fact that the theory of operation is the same as in the primary ignition system, but on a much larger scale.  Instead of using a permanent magnet to stimulate electron movement, we will be using an electromagnet which is turned on and off by the ignition module using the primary signal.  We will compare a point controlled distributor to an electronic ignition distributor so the students can see the ignition coil being turned on and off.  We will then discuss transistor function and the fact that a transistor is just a switch with no moving parts.  I will explain that an ignition system needs to produce 8,000 to 10,ooo volts to idle and that some ignition systems are producing 40,000 to 60,000 volts under load.  How do we get that from 12 volts?  A step up transformer!  Using a white board, calculators and Ohm's law (which we are acquainted with from our electrical section!), we will compare the 1 ohm resistance of the primary side to the 5,000 ohm resistance of the secondary side and determine that 12 volts can easily be transformed into 60,000 volts with about 14 amps of current flow.  Enough math, let's go look at it on the scope!

• Ignition scope Lab / Shop

Using the two dual trace ignition scopes in the shop and various vehicles, students can break up into their work groups and view primary and secondary ignition patterns.  We then substitute bad ignition wires, install an inline spark tester, increase spark plug gaps etc. to see what different conditions look like in the ignition patterns.  Students are encouraged to look for anomolies and attempt to determine the cause.

### Assessment

Assessment Types:
Projects, Observations,

Using demonstration vehicles, each work group will create an ignition system problem by substituting failed parts, opening or closing spark plug gaps, crossing ignition wires, and my personal favorite, putting a pencil eraser down one of the distributor cap towers.  Students then move from vehicle to vehicle and attempt to locate the cause and effect of the problems.  This is more of a fun activity than an actual test and students gain experience tracking different types of ignition system failures.  Participating students are given a sticker to place on their classroom charts.