See Figures 1 and 2
With the ignition switch ON , the primary circuit is on and the ignition coil is energized. When the armature spokes approach the magnetic pickup coil assembly, they induce the voltage which tells the amplifier to turn the coil primary current off. A timing circuit in the amplifier module will turn the current on again after the coil field has collapsed. When the current is on, it flows from the battery through the ignition switch, the primary windings of the ignition coil, and through the amplifier module circuits to ground. When the current is off, the magnetic field built up in the ignition coil is allowed to collapse, inducing a high voltage into the secondary windings of the coil. High voltage is produced each time the field is thus built up and collapsed. When DuraSpark is used in conjunction with the EEC, the EEC computer tells the DuraSpark module when to turn the coil primary current off or on. In this case, the armature position is only a reference signal of engine timing, used by the EEC computer in combination with other reference signals to determine optimum ignition spark timing.
The high voltage flows through the coil high tension lead to the distributor cap where the rotor distributes it to one of the spark plug terminals in the distributor cap. This process is repeated for every power stroke of the engine.
Ignition system troubles are caused by a failure in the primary and/or the secondary circuit, incorrect ignition timing or incorrect distributor advance. Circuit failures may be caused by shorts, corroded or dirty terminals, loose connections, defective wire insulation, cracked distributor cap or rotor, defective pick-up coil assembly or amplifier module, defective distributor points or fouled spark plugs.
If an engine starting or operating trouble is attributed to the ignition system, start the engine and verify the complaint. On engines that will not start, be sure that there is gasoline in the fuel tank and the fuel is reaching the carburetor. Then locate the ignition system problem using the following procedures.
DIAGNOSIS AND TESTING
See Figures 3, 4, 5, 6, 7 and 8
The following procedures can be used to determine whether the ignition system is working or not. If these procedures fail to correct the problem, a full troubleshooting procedure should be performed.Preliminary Checks
- Check the battery's state of charge and connections.
- Inspect all wires and connections for breaks, cuts, abrasions, or burned spots. Repair as necessary.
- Unplug all connectors one at a time and inspect for corroded or burned contacts. Repair and plug connectors back together. DO NOT remove the dielectric compound in the connectors.
- Check for loose or damaged spark plug or coil wires. A wire resistance check is given at the end of this section. If the boots or nipples are removed on 8mm ignition wires, recoat the inside of each with new silicone dielectric compound (Motorcraft WA-10).
See Figures 9, 10, 11, 12, 13 and 14
To perform the following tests, two special tools are needed; the ignition test jumper shown in the illustration and a modified spark plug. Use the illustration to assembly the ignition test jumper. The test jumper must be used when performing the following tests. The modified spark plug is basically a spark plug with the side electrode removed. Ford makes a special tool called a Spark Tester for this purpose, which besides not having a side electrode is equipped with a spring clip so that it can be grounded to engine metal. It is recommended that the Spark Tester be used as there is less change of being shocked.Run Mode Spark Test
The wire colors given here are the main colors of the wires, not the dots or hash marks.STEP 1
- Remove the distributor cap and rotor from the distributor.
- With the ignition off, turn the engine over by hand until one of the teeth on the distributor armature aligns with the magnet in the pickup coil.
- Remove the coil wire from the distributor cap. Install the modified spark plug (see Special Tools, above) in the coil wire terminal and using heavy gloves and insulated pliers, hold the spark plug shell against the engine block.
- Turn the ignition to RUN (not START) and tap the distributor body with a screwdriver handle. There should be a spark at the modified spark plug or at the coil wire terminal.
- If a good spark is evident, the primary circuit is OK: perform the Start Mode Spark Test. If there is no spark, proceed to STEP 2.
- Unplug the module connector(s) which contain(s) the green and black module leads.
- In the harness side of the connector(s), connect the special test jumper (see Special Tools, above) between the leads which connect to the green and black leads of the module pig tails. Use paper clips on connector socket holes to make contact. Do not allow clips to ground.
- Turn the ignition switch to RUN (not START) and close the test jumper switch. Leave closed for about 1 second, then open. Repeat several times. There should be a spark each time the switch is opened.
- If there is no spark, the problem is probably in the primary circuit through the ignition switch, the coil, the green lead or the black lead, or the ground connection in the distributor; Perform STEP 3. If there is a spark, the primary circuit wiring and coil are probably OK. The problem is probably in the distributor pick-up, the module red wire, or the module: perform STEP 6.
- Disconnect the test jumper lead from the black lead and connect it to a good ground. Turn the test jumper switch on and off several times as in STEP 2.
- If there is no spark, the problem is probably in the green lead, the coil, or the coil feed circuit: perform STEP 5.
- If there is spark, the problem is probably in the black lead or the distributor ground connection: perform STEP 4.
- Connect an ohmmeter between the black lead and ground. With the meter on its lowest scale, there should be no measurable resistance in the circuit. If there is resistance, check the distributor ground connection and the black lead from the module. Repair as necessary, remove the ohmmeter, plug in all connections and repeat STEP 1.
- If there is no resistance, the primary ground wiring is OK: perform STEP 6.
- Disconnect the test jumper from the green lead and ground and connect it between the TACH-TEST terminal of the coil and a good ground to the engine.
- With the ignition switch in the RUN position, turn the jumper switch on. Hold it on for about 1 second then turn it off as in Step 2. Repeat several times. There should be a spark each time the switch in turned off. If there is no spark, the problem is probably in the primary circuit running through the ignition switch to the coil BAT terminal, or in the coil itself. Check coil resistance (test given later in this section), and check the coil for internal shorts or opens. Check the coil feed circuit for opens, shorts, or high resistance. Repair as necessary, reconnect all connectors and repeat STEP 1. If there is spark, the coil and its feed circuit are OK. The problem could be in the green lead between the coil and the module. Check for an open or short, repair as necessary, reconnect all connectors and repeat STEP 1.
To perform this step, a voltmeter which is not combined with a dwell meter is needed. The slight needle oscillations ( 1 / 2 v) you'll be looking for may not be detectable on the combined voltmeter/dwell meter unit.
- Connect a voltmeter between the orange and purple leads on the harness side of the module connectors.
- Set the voltmeter on its lowest scale and crank the engine. The meter needle should oscillate slightly (about 1 / 2 v). If the meter does not oscillate, check the circuit through the magnetic pick-up in the distributor for open, shorts, shorts to ground and resistance. Resistance between the orange and purple leads should be 400-1,000 ohms, and between each lead and ground should be more than 70,000 ohms. Repair as necessary, reconnect all connectors and repeat STEP 1.
If the meter oscillates, the problem is probably in the power feed to the module (red wire) or in the module itself: proceed to STEP 7.STEP 7
- Remove all meters and jumpers and plug in all connectors.
- Turn the ignition switch to the RUN position and measure voltage between the battery positive terminal and engine ground. It should be 12 volts.
- Next, measure voltage between the red lead of the module and engine ground. To mark this measurement, it will be necessary to pierce the red wire with a straight pin and connect the voltmeter to the straight pin and to ground. DO NOT ALLOW THE STRAIGHT PIN TO GROUND ITSELF!
- The two readings should be within one volt of each other. If not within one volt, the problem is in the power feed to the red lead. Check for shorts, open, or high resistance and correct as necessary. After repairs, repeat Step 1.If the readings are within one volt, the problem is probably in the module. Replace it with a good module and repeat STEP 1. If this corrects the problem, reconnect the old module and repeat STEP 1. If the problem returns, permanently install the new module.
The wire colors given here are the main colors of the wires, not the dots or hash marks.
- Remove the coil wire from the distributor cap. Install the modified spark plug mentioned under Special Tools, above, in the coil wire and ground it to engine metal either by its spring clip (Spark Tester) or by holding the spark plug shell against the engine block with insulated pliers.
See CAUTION under STEP 6 of Run Mode Spark Test, above.
- Have an assistant crank the engine using the ignition switch and check for spark. If there is good spark, the problem is probably in distributor cap, rotor, ignition cables or spark plugs. If there is no spark, proceed to Step 3.
- Measure the battery voltage. Next, measure the voltage at the white wire of the module while cranking the engine. To mark this measurement, it will be necessary to pierce the white wire with a straight pin and connect the voltmeter to the straight pin and to ground. DO NOT ALLOW THE STRAIGHT PIN TO GROUND ITSELF. The battery voltage and the voltage at the white wire should be within 1 volt of each other. If the readings are not within 1 volt of each other, check and repair the feed through the ignition switch to the white wire. Recheck for spark (Step 1). If the readings are within 1 volt of each other, or if there is still no spark after the power feed to white wire is repaired, proceed to Step 4.
- Measure the coil BAT terminal voltage while cranking the engine. The reading should be within 1 volt of battery voltage. If the readings are not within 1 volt of each other, check and repair the feed through the ignition switch to the coil. If the readings are within 1 volt of each other, the problem is probably in the ignition module. Substitute another module and repeat the test for spark (Step 1).