BASIC OPERATING PRINCIPLES
The Ford Solid State Ignition is a pulse triggered, transistor controlled breakerless ignition system. With the ignition switch ON, the primary circuit is on and the ignition coil is energized. When the armature spokes approach the magnetic pick-up coil assembly, they induce a 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 second windings of the coil. High voltage is produced each time the field is thus built up and collapsed.
Although the systems are basically the same, Ford refers to their solid state ignition in several different ways. 1976 systems are referred to simply as Breakerless systems. In 1977, Ford named their ignition system Dura Spark I and Dura Spark II. In 1982 Ford dropped the Dura Spark I and introduced the Dura Spark III. This system is based on Electronic Engine Control (EEC). The EEC system controls spark advance in response to various engine sensors. This includes a crankshaft position sensor which replaces the stator and armature assembly in the distributor. Dura Spark II is the version used in all states except California. Dura Spark I and III are the systems used in California V8's only. Basically, the only difference between the two is that the coil charging currents are higher in the California vehicles. This is necessary to fire the leaner fuel/air mixtures required by California's stricter emission laws. The difference in coils alters some of the test values.
Ford has used several different types of wiring harness on their solid state ignition systems, due to internal circuitry changes in the electronic module. Wire continuity and color have not been changed, but the arrangement of the terminals in the connectors is different for each year. Schematics of the different years are included here, but keep in mind that the wiring in all diagrams has been simplified and as a result, the routing of your wiring may not match the wiring in the diagram. However, the wire colors and terminal connections are the same.
Wire color coding is critical to servicing the Ford Solid State Ignition. Battery current reaches the electronic module through either the white or red wire, depending on whether the engine is cranking or running. When the engine is cranking, battery current is flowing through the white wire. When the engine is running, battery current flows through the red wire. All distributor signals flow through the orange and purple wires. The green wire carries primary current from the coil to the module. The black wire is a ground between the distributor and the module. In 1976, the blue wire was dropped when the zener diode was added to the module. The orange and purple wires which run from the stator to the module must always be connected to the same color wire at the module. If these connections are crossed, polarity will be reversed and the system will be thrown out of phase. Some replacement wiring harnesses were sold with the wiring crossed, which complicates the problem considerably. As previously noted, the black wire is the ground wire. The screw which grounds the black wire, also, of course, grounds the engine primary circuit. If this screw is loose, dirty, or corroded, a seemingly incomprehensible ignition problem will develop. Several other cautions should be noted here. Keep in mind that on vehicles equipped with catalytic converters, any test that requires removal of a spark plug wire while the engine is running should be kept to a thirty second maximum. Any longer than this may damage the converter. In the event you are testing spark plug wires, do not pierce them. Test the wires at their terminals only.TROUBLESHOOTING THE FORD SOLID STATE IGNITION SYSTEM
See Figures 1, 2 and 3
Fig. 1: Dura Spark II V8 distributor Fig. 2: 1976 test sequence Fig. 3: 1977-80 test sequence
Ford has substantially altered their 1978-86 electronic ignition test procedure. Due to the sensitive nature of the system and the complexity of the test procedures, it is recommended that you refer to your dealer if you suspect a problem in your 1978-86 electronic ignition system. The system can, of course, be tested by substituting known good components (module, stator, etc.).
This system, which at first appears to be extremely complicated, is actually quite simple to diagnose and repair. Diagnosis does, however, require the use of a voltmeter and an ohmmeter. You will also need several jumper wires with both blade ends and alligator clips.
The symptoms of a defective component within the solid state system are exactly the same as those you would encounter in a conventional system. Some of these symptoms are:
- Hard or no starting
- Rough idle
- Poor fuel economy
- Engine misses while under load or while accelerating
If you suspect a problem in your ignition system, first perform a spark intensity test to pinpoint the problem. Using insulated pliers, hold the end of one of the spark plug leads about 1/2 inch; (12.7mm) away from the engine block or other good ground, and crank the engine. If you have a nice, fat spark, then your problem is not in the ignition system. If you have no spark or a very weak spark, then proceed to the following tests.
See Figure 4
Fig. 4: V8 distributor components
To test the stator (also known as the magnetic pickup assembly), you will need an ohmmeter. Run the engine until it reaches operating temperature, then turn the ignition switch to the off position. Disconnect the wire harness from the distributor. Connect the ohmmeter between the orange and purple wires. Resistance should be 400-800?. Next, connect the ohmmeter between the black wire and a good ground on the engine. Operate the vacuum advance either by hand or with an external vacuum source. Resistance should be 0?. Finally, connect the ohmmeter between the orange wire and ground, and then purple wire and ground. Resistance should be over 70,000? in both cases. If any of your ohmmeter readings differ from the above specifications, then the stator is defective and must be replaced as a unit.
If the stator is good, then either the electronic module or the wiring connections must be checked next. Because of its complicated electronic nature, the module itself cannot be checked, except by substitution. If you have access to a module which you know to be good, then perform a substitution test at this time. If this cures the problem, then the original module is faulty and must be replaced. If it does not cure the problem or if you cannot locate a known good module, then disconnect the two wiring harnesses from the module, and, using a voltmeter, check the following circuits.
Make no tests at the module side of the connectors.
- Starting circuit: Connect the voltmeter leads to ground and to the corresponding female socket of the white male lead from the module (you will need a jumper wire with a blade end). Crank the engine over. The voltage should be between 8 and 12 volts.
- Running circuit: Turn the ignition switch to the ON position. Connect the voltmeter leads to ground and the corresponding female socket of the red male lead from the module. Voltage should be battery voltage plus or minus 0.1 volts.
- Coil circuit: Leave the ignition switch ON. Connect the voltmeter leads to ground and to the corresponding female socket of the green male lead from the module. Voltage should be battery voltage plus or minus 0.1 volts.
If any of the preceding readings are incorrect, inspect and repair any loose, broken, frayed or dirty connections. If this doesn't solve the problem, perform a battery source test.
Battery Source Test
To make this test, do not disconnect the coil.
Connect the voltmeter leads to the BAT terminal at the coil and a good ground. Connect a jumper wire from the DEC terminal at the coil to a good ground. Make sure all lights and accessories are off. Turn the ignition to the ON position. Check the voltage. If the voltage is below 4.9 volts (11 volts for Dura Spark I), then check the primary wiring for broken strands, cracked or frayed wires, or loose or dirty terminals. Repair or replace any defects. If, however, the voltage is above 7.9 volts (14 volts for Dura Spark I), then you have a problem in the resistance wiring and it must be replaced.
It should be noted here that if you do have a problem in your electronic ignition system, most of the time it will be a case of loose, dirty or frayed wires. The electronic module, being completely solid state, is not ordinarily subject to failure. It is possible for the unit to fail, of course, but as a general rule, the source of an ignition system probably will be somewhere else in the circuit.IGNITION COIL TEST
The ignition coil must be diagnosed separately from the rest of the ignition system.
SPARK PLUG WIRE RESISTANCE
- Primary resistance is measured between the two primary (low voltage) coil terminals, with the coil connector disconnected and the ignition switch off. Primary resistance should be 0.3-1.0?.
- On Dura Spark ignitions, the secondary resistance is measured between the BATT and high voltage (secondary) terminals of the ignition coil with the ignition off, and the wiring from the coil disconnected. Secondary resistance must be 8,000-11,500?.
- If resistance tests are okay, but the coil is still suspected, test the coil on a coil tester by following the test equipment manufacturer's instructions for a standard coil. If the reading differs from the original test, check for a defective harness.
Resistance on these wires must not exceed 5,000? per foot. To properly measure this, remove the wires from the plugs, and remove the distributor cap. Measure the resistance through the distributor cap at that end. Do not pierce any ignition wire for any reason. Measure only from the two ends.
Silicone grease must be re-applied to the spark plug wires whenever they are removed. When removing the wires from the spark plugs, a special tool should be used. do not pull on the wires. Grasp and twist the boot to remove the wire. Whenever the high tension wires are removed from the plugs, coil, or distributor, silicone grease must be applied to the boot before reconnection. Use a clean small screwdriver blase to coat the entire interior surface with Ford silicone grease D7AZ-19A331-A, Dow Corning #111, or General Electric G-627.SYSTEM OPERATION
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 cylinders. Then locate the ignition system problem using the following procedures.TROUBLESHOOTING DURASPARK II
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.
See Figures 5 and 6
Fig. 5: V8 static timing position Fig. 6: When working on the electronic ignition, unplug the module connectors here. Leave the module side alone or you'll short out the module
- Check the battery's state of charge and connections.
- Inspect all wires and connections for breaks, cuts, abrasions, or burn 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, reline the inside of each with new silicone dielectric compound (Motorcraft WA-10).
See Figures 7 and 8
Fig. 7: Attaching a tachometer lead to the coil connector Fig. 8: Removing the coil-to-distributor lead
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 chance of being shocked.
See Figures 9, 10, 11 and 12
Fig. 9: Checking igntion wire resistance Fig. 10: Removing the distributor cap Fig. 11: Silicone compound application on the rotor Fig. 12: Loosening the distributor holddown bolt
The wire colors given here are the main colors of the wires, not the dots or hashmarks.
- 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 (1/2V) 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.
On catalytic converter equipped cars, disconnect the air supply line between the Thermactor by-pass valve and the manifold before cranking the engine with the ignition off. This will prevent damage to the catalytic converter. After testing, run the engine for at least 3 minutes before reconnecting the by-pass valve, to clear excess fuel from the exhaust system.
- Set the voltmeter on its lowest scale and crank the engine. The meter needle should oscillate slightly (about 1/2V). 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?, and between each lead and ground should be more than 70,000?. 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.
- 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 BE GROUNDED!
- 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.
Start Mode Spark Test
The wire colors given here are the main colors of the wires, not the dots or hashmarks.
- 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 BE GROUNDED. 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).