When your engine begins to skip and misfire, or won't start at all, one of its basic needs is not being met. It may be a fault in the ignition system. To help in the process of isolating ignition system problems, it's helpful to know exactly what the ignition system must do on your engine.
Manufacturers have devised slightly different methods to achieve the same goal, which is to create an electrical spark capable of blasting its way through a dense, compressed fog of fuel, oil, and air with enough heat to set it alight.
This spark must be delivered to the correct cylinder at the correct time, and with equal intensity for all cylinders. In addition, as the engine speed changes, so must the timing. On today's engines, these tasks are undertaken by a combination of solid state devices, electronic wizardry, and a mechanical linkage to advance the ignition timing. Figure 5-1 shows a typical outboard engine ignition system with all the key components named.
On outboard ignition systems, some of the primary operating components are located under the flywheel, so, as with some of the other procedures mentioned in this book, you may need the services of a trained mechanic with the correct puller tool to reach these parts. Also, test procedures in workshop manuals will typically call for the use of special tools and testers for troubleshooting ignition systems. This equipment is quite expensive, and really has no place in your tool kit unless you do this sort of work daily. So there are a few things you'll have to leave to the experts. But this chapter will show you how to figure out the most common ignition problems with the use of simple tools, and a multimeter that you really should have in your tool collection anyway.
Figure 5-1. Outboard engine capacitive discharge ignition system.
If your engine was built after about 1975, it most likely has some variation of a capacitive discharge (CD) ignition system. This system "charges up" a capacitor or condenser, a simple device capable of storing an electric charge and discharging it very rapidly. The charge then goes to the appropriate ignition coil. Different manufacturers use various names to describe the CD components they use, but they're all quite similar.
Since the first edition of Outboard Engines, midsized to large engine ignition systems have evolved into computerized marvels. Despite this evolution, however, many of the components in the system serve essentially the same function as they did in earlier electronic ignition systems. In fact, with smaller carbureted engines, the basic ignition systems are essentially the same as earlier capacitive discharge (CD) systems. The essential difference between earlier and newer engine ignition systems is that rather than using a simple CDI unit, the newest engines have an onboard computer that typically integrates ignition and electronic fuel injection functions into one "box." What happens is that some of the ignition components, such as the sensor coils, become data input devices for the computer, and components such as the high-voltage ignition coils are now thought of as output devices. Let's look at the key components of a typical ignition system one by one and learn about their function in the system.
The engine's flywheel contains magnets carefully positioned to create an electric current as they rotate past specially designed coils of wire. Current is created by magnetic induction. Simply put, that means that a magnet moving rapidly near a conductor will induce electrical flow within the conductor.
Conversely, a wire that moves rapidly through a magnetic field will also generate electrical flow. This principle governs the working of electric motors, alternators, and generators.
So as the flywheel spins, alternating current (AC) is produced in the charge coils, which are located under the flywheel. The AC is then converted to direct current (DC) by a diode-type rectifier located inside the onboard computer. This computer has various names, depending on the engine maker: electronic control module (ECM), electronic control unit (ECU), ignition control module (ICM), and engine management module (EMM). Next this voltage is sent to a capacitor inside the module, where it builds up a charge (capacitors are solid-state devices that store electrical energy).
Once fully charged, what Mercury refers to as a "gate signal" is applied and the computer directs the capacitor to discharge. This gate signal is supplied by yet another set of coils, or in some cases what's known as a Hall effect sensor, strategically located under the flywheel. Depending on the manufacturer, other names for this sensor can be simply sensor coils, pulsar coils, trigger coils, or, on modern engines, crankshaft position sensors (CPS) or ignition pulse generators. The voltage is sent to the high-tension ignition coils, where it runs through the primary windings of the coils. It's in these coils that some of the real magic occurs. The secondary windings in the ignition coils elevate the voltage levels to anywhere from 15,000 to 40,000 or more volts to fire the spark plugs. Figure 5-2 illustrates these primary and secondary windings. Figure 5-3 shows a more modern ignition coil. This coil type actually connects directly to the spark plug, one for each cylinder, and eliminates the need for a high-tension spark plug wire, historically a fairly vulnerable component in any ignition system.
Relative to ignition timing, the method used depends on the specific ignition system. On smaller, carbureted engines the sensor, or trigger coil, is mounted on a plate under the flywheel that is linked to the throttle
Figure 5-2. High-tension coil—internal construction.
Figure 5-3. A modern ignition coil.
linkage. As engine rpm increases, the throttle position changes, and, in turn, the relative location of the sensor coil to the magnets under the flywheel also changes. This movement of the sensor coil(s) is what "advances" the timing to appropriately deal with increased engine rpm.
On the newer fuel injected engines, additional computer data inputs often include such things as cooling water temperature, oil pressure, intake manifold pressure, air temperature, and fuel injection timing and duration. All of this data contributes to extremely precise ignition timing based on a combination of engine-specific and environmental changes. Additionally, most of the modules in use for the last 20 years have the ability to limit engine maximum rpm to prevent over-revving. Some modules even automatically reduce engine speed if the engine begins to run too hot for any reason.
As you saw above, the voltage from the module goes to the primary winding of the ignition coil, or high-tension coil. You may know this type of coil as a step-up transformer. As already stated, the voltage is stepped up to between 15,000 and 40,000 volts. That's the kind of voltage needed to jump the air gap we talked about before, and ignite the air/fuel mixture in the cylinder. Your high-tension ignition coil has two "sides," the primary and the secondary. It is really two coil assemblies combined into one neat, compact case.
Figure 5-2 shows the internal construction of a typical ignition coil, with its primary and secondary windings. It also uses the principle of magnetic induction, with the magnetism generated by the primary (lower voltage) winding creating a magnetic field around the secondary winding, which you will notice has many more windings than the primary coil. The ignition module controls the rapid turning on and off of electrical flow in the primary winding, thereby turning this magnetic field on and off. The effect of this is the same as described earlier. The rapid movement of this magnetic field past the secondary windings induces electrical current flow. The greater the number of turns of wire in the secondary winding, the higher the voltage produced.
As this secondary voltage leaves the center tower of the ignition coil, it travels along the spark-plug wire, which is heavily insulated and designed to carry this high voltage. In the case of the newer style coils shown in Figure 5-3, it goes directly to the spark plug.
If all is well, the high voltage will jump the gap in the spark plug between the center electrode and the ground electrode. On larger engines with surface-gap plugs, the high-voltage current will jump from the center electrode to the side of the plug assembly itself, completing a circuit to "ground"—the engine block the plug is threaded into.
Last, but certainly not least, is the stop control. You need a means to shut your engine off, and a good way is to stop the spark plugs working. Depending on your engine, this may be accomplished by a simple stop button, or a key switch on larger engines, that disables the whole ignition system. On newer engines, you'll find an emergency stop button with an overboard clip and lanyard attachment. This system is wired directly to your system's ignition module (power pack). It functions by creating a momentary short-circuit inside the CDI power pack, grounding the current intended for the high-tension coils and thus shutting off the ignition long enough to stop the engine. Faulty stop circuits are frequently the cause of a no-spark condition; test procedures for this circuit are outlined later in this chapter on page 40.
As with any electrical circuit testing, the first step should be to look for the obvious. Whenever a problem develops with any engine or system that has been regularly maintained, troubles that crop up are almost always due to some minor oversight, and easily solved.
• Check all the wiring hook-ups for loose connections.
• Look for signs of corrosion on terminals and at connectors.
• Check for any broken or frayed wires.
• Make certain the problem is not something as silly as a blown fuse.
Any of these things can be the cause of ignition problems—but they can be fixed quickly with basic tools.
The next step in checking out your ignition system is to verify that you're getting spark to each cylinder. When you're doing this it's extremely important that you check for fuel leaks. Make certain all fuel-line fittings and connections are secure.
Incidentally, if you're working in bright daylight, it's a good idea to create some shade near the plug wire you're checking. It's very difficult to see a spark in sunlight.
Figure 5-6 shows the neon tester hooked up and ready to go. Hold the tool so you can see the neon flash when it occurs. You should see a bright orange flash if a good spark is being delivered. It's a bit subjective, but the brightness of the flash is proportional to the strength of the spark being delivered. On modern systems, you want to see a really bright flash each time the ignition coil fires.
If your engine is skipping or misfiring, you should check all of the plug wires this way to be certain that each secondary coil is sending spark through its respective plug wire to the plug.
By the way, be careful not to mix the plug wires up when you perform this test; each wire is timed to a specific cylinder. Make sure the emergency stop button and clip are set correctly if your engine is so equipped. (It's amazing how easy it is to forget this simple device.) Check for spark again. If spark is still not evident, further investigation will be needed.
Unfortunately, there's no guarantee that if you get an appropriately hefty electrical current to the spark plugs, they'll fire. They may simply be worn out. And
Figure 5-4. A surface-gap spark plug (left) and a conventional plug.
Figure 5-5. Using a spark plug gapping tool.
Figure 5-6. The neon tester in place and ready to use.
many other things can cause a plug in your engine not to fire.
For example, too much oil in the fuel is a primary cause of spark-plug failure. So is the use of a plug with an incorrect heat range. Problems with the fuel system also can result in spark-plug failure.
Now, if you've been conscientious and serviced your engine regularly as described in Chapter 3, worn-out plugs shouldn't be a consideration. What does that leave? A visual check of the plugs, and verification that the plug itself can actually fire.
Remove the plug, using the appropriate spark-plug socket or the plug removal tool supplied in the tool kit for your engine, and look it over. Is it soaked with a black fuel/oil mixture? Are the center and ground electrodes intact?
If the plug's center and ground electrodes are okay, and the plug is gapped correctly, check the number on the plug and compare it with the manufacturer's recommendations. It may be the wrong heat range for the engine.
If all of these things check out okay, then insert the plug into its correct plug wire boot, and wedge the plug into a spot on the side of your engine as shown in Figure 5-7, being sure that the metal case of the plug is grounded.
Crank the engine over. If you see a spark jumping from the center electrode to the edge of the plug on a surface-gap plug, or to the ground electrode on a standard unit, and it's blue in color, then it's okay and should fire in the cylinder. If no spark is evident, or it's weak and yellow, and you are certain (from your previous spark intensity check) that adequate current is getting to the plug, then the plug must be replaced. If it's a standard plug, make sure to check the gap before installing the new plug, as shown in Figure 5-4. Surface-gap plugs require no adjustment.
When you've had a bit of experience, you'll find that your spark plugs are valuable diagnostic tools. Whenever you remove your plugs, keep them in order according to the cylinders they came from and check each plug over carefully, looking for any cracks in the ceramic body or insulator, black oily build-up, or discoloration.
A spark plug that is burning correctly will show a light brown "fluffy" coloration on the center electrode's ceramic insulator, and a fluffy black coloration on the metal base, with the exception of the ground electrode itself, which will show a light gray/brown color.
Figure 5-7. Testing a spark plug on the engine block.
Several additional points regarding spark plugs need to be made. First, you need to be careful not to over-torque (screw them in too tightly) them into the cylinder head when installing them. It's a good idea to put a light coating of white grease on the threads before screwing them back into the cylinder head. Screw them in by hand until the sealing washer seats, and then use your special plug tool or socket and ratchet to tighten them an additional quarter to half a turn. Any more may damage the threads in the cylinder head.
Additionally, if your engine is fuel injected, it's a good idea to "key" the plug so that the gap between the ground electrode and the center electrode faces the fuel injector nozzle in the combustion chamber. If your engine calls for surface gap plugs, there's no problem, but with more conventional plugs, having the spark right in the face of the injector spray helps maximize combustion. In this case the method varies depending on whether your spark plug is recessed deeply into a cavity in the cylinder head or surface mounted. You should be able to identify the location of the fuel injector by looking for the fuel hoses and a wired plug on the injector. With surface-mounted plugs, simply mark the electrode gap side of the socket you are using with a permanent marker and screw the plug into the head. When it's finally tightened, you want the marker line pointing toward the injector. With recessed plugs, put a marker line on the ratchet end of the extension you use to gain reach, and line it up facing the injector.
If you have performed the spark checks described above, and determined that you have no spark at any of the cylinders, or spark at some and not others, then further investigation is needed.
The following checklist is designed to organize your search through the ignition system, and the tests that follow will help you to pinpoint the source of the problem. Remember, these tests should be performed by using this book and the manual for your particular engine.
Each manufacturer uses different wire-color codes, and slightly different test procedures for their respective systems, but by following this guide you should be able to trace through your system and isolate any CD ignition system problems, in the rare instance that they occur.
One last reminder: These test sequences assume that you have already eliminated the possibility of a fuel-related or compression-related problem.
1. Begin by checking to see if your engine is equipped with a fuse for the ignition system. If it is, check the fuse, and replace it if needed.
2. Check the plug wires.
3. Test the ignition coils.
4. Test the outputs of the charge coil, sensor coil, and ignition module if specifications are given in the workshop manual. You may need to use the DVA tester (part number 511-9773(a)—see Chapter 3). With some engines you may be simply measuring resistance values for these components using your ohmmeter.
5. Test all engine stop circuits.
6. Test the mercury tilt switch if your engine is equipped with one.
Detailed procedures follow for each of these checks.
Here's a nice easy job. If you have already used the spark tester and seen a spark at the plug end of the wire, then you know the wire is conducting electricity to the plug. But that's not all the wire has to do. It also has to insulate this high-voltage electricity under all engine operating conditions. It has to conduct electricity on a vibrating engine when your boat is underway, and stop the electricity leaking out to the many metal components all around it, which would ground it.
So start with a visual inspection of the wire and the wire ends inside the protective boots. Look for any sign of cracking, spots where the insulating material has been worn away due to chafing with some part of your engine, and any sign of green corrosion on the metal clips that lock the wire end to the coil and spark plug. If corrosion is evident, slide the wire boot back onto the wire and carefully clean the metal connector with a wire brush until the metal is bright and shiny. If the wire is chafed or cracked, replace it.
For further checks, you'll need your multimeter. Set the meter on the low ohms scale and insert the meter probes into the wire as shown in Figure 5-9. The meter should read near zero ohms. Next, hold the meter probes in place and bend and flex the wire while you watch the meter carefully. If the meter fluctuates, there is a break in the wire inside the insulation. Replace the wire. When reinstalling wires, make sure to use the wire hold-downs found on many engines. These hold-downs are there to keep the wire from coming in contact with moving parts of the engine that may cause chafe and ultimately wire failure. Also, all manufacturers recommend applying a light coating of nonconductive waterproof grease on the ribbed ceramic insulator and metal connector of the spark plug and coil connector before reinstalling the plug wire. This grease will help the boot to seal out moisture that would eventually corrode the metal connector end of the plug wire.
Figure 5-8. Properly burning spark plugs look like these. They should have a light-brown center electrode insulator, with a light fluffy black color around the perimeter of the plug.
Figure 5-9. Using the ohmmeter to test a plug wire.
A technician in a repair shop will normally be using a laptop computer with proprietary software or a specialized (again, proprietary) tester to perform engine diagnostic procedures. These units are quite expensive and don't need to be a part of your tool collection. This means you won't be able to perform some of the more advanced ignition system tests. But if you have a multimeter, a spray bottle filled with fresh water, and the spark tester already mentioned, you'll be well equipped to track down most ignition faults. At the very least, you'll be able to point the professional mechanic in the right direction, saving yourself expensive labor charges.
As we've already seen, your ignition coil is really two coils combined into one unit. It consists of two sets of wire windings, a primary winding and a secondary winding. The trick is to identify which external wires and connections go to which coil inside the insulated case. To find out, you'll need the wiring diagram and workshop manual for your engine. Refer to the wiring diagram and check the resistance of each of the coils with your multimeter's ohmmeter. If electrical continuity and normal resistance is shown with these tests, you can be reasonably certain your coils are okay. If you discover excessive resistance, or if the meter indicates an open circuit in the coil, the coil must be replaced.
Figure 5-10 shows these tests being performed on a typical outboard engine high-tension coil. But please remember that it's absolutely vital to identify the wires
Figure 5-10. (Top) Testing the primary winding. (Bottom) Testing the secondary winding.
correctly so you can ascertain their relative resistance values.
Incidentally, whenever you remove an ignition coil from your engine, be extremely careful to note the location of any insulating washers located under the coils or their hold-down bolts. If you misplace this insulation it's likely that even a perfectly good coil won't work.
Another simple test for this part of your ignition system is to spray fresh water over the ignition coils, plug wires, and spark plugs while the engine's running. Do this in the shade, or at dusk. Any problems will immediately show as sparks, jumping from the poorly insulated wire or connection. The faulty component will have to be replaced.
For these tests you will again need your engine's workshop manual. Remember, your charge coil and sensor coil lie under the flywheel, and you can't see them unless you remove it. Unfortunately, flywheel removal goes beyond routine testing, and is not within the scope of this book, but there are still several useful tests you can perform. For example, you can test the charge coils and sensor coils for continuity and a possible short to ground. You can also test their voltage output using the Mercury DVA tester in conjunction with your multimeter.
Just like your high-tension coil, these coils consist of a tightly wound length of wire, insulated from the ground in most cases. In all cases, the charge coil will have a greater designed resistance than the sensor coil. The reason for this is that the charge coil must generate higher voltage than the sensor coils. This means the length of wire in the coil will be much longer, and therefore have more inherent resistance.
The wiring harness for these coils is always secured to the movable timing plate under the flywheel and usually exits from under this assembly on the starboard side (right side, looking toward the bow of the boat) of the engine powerhead. Once you have located the harness
Figure 5-11. Testing charge and sensor coils. Note the point at which the wiring harness exits from under the flywheel, and the timing-plate assembly.
and found all the wires that come through it, use the wiring diagram to identify the wires attached to the charge and sensor coils. These wires will often end up at a gang plug assembly for connection to your ignition module. Unplug this connection to continue testing.
To test the charge coil, set your ohmmeter to the appropriate scale for the expected resistance as specified in your engine manual. Insert your meter's red and black test probes into the plug socket terminal that matches the correct color wire, and take the reading.
Charge coils generally have a resistance of 400 to 900 ohms. If the reading is more than specified, or indicates a break in the wiring (infinite reading), the charge coil is defective, and will have to be replaced.
Next, you must check for a short to ground. To perform this test, simply remove one of the meter's test leads from the plug assembly, switch your meter to its high ohms scale, and touch the free lead to the metal timing plate the harness is secured to. Any movement of the meter needle indicates a short to ground caused by frayed or melted insulation, or by a bad charge coil. In both cases the flywheel will have to be removed to fix the problem.
To test a sensor coil for continuity and a short to ground, follow the exact procedure given above for the charge-coil tests, only remember to adjust your meter for a much lower resistance reading, usually between 15 and 50 ohms.
For the short-to-ground test, the meter will be set on the same high scale as for the charge-coil short test. Remember to test all sensor coils in this manner if your engine is equipped with more than one.
On new engines, this "coil" may actually be a Hall effect sensor, in which case an ohmmeter test will tell you nothing. Although specialized testers are available to test Hall effect sensors in automotive applications, I'm not aware of one available as a dedicated device for outboard engine applications. The proprietary testers already discussed can check output signals, but for the owner-mechanic, this test isn't possible and it requires dealer testing.
To test for voltage output from these coils you will need to use the DVA adapter as shown in Figure 5-12. This device will convert the AC voltage from your charge and sensor coils to a DC voltage your multimeter can read. The readings you get here will not only test the performance of these coils but also verify that the magnets under your flywheel still have sufficient magnetism. Voltage output is directly proportional to the cranking speed of the engine and the strength of these magnets.
To test output, simply plug the red lead from the tester into the DC voltage socket on your multimeter and the black lead from the tester into the ground or negative socket on your meter. Next, plug the red and black leads from your meter into the corresponding sockets on the DVA tester. You're ready to take a voltage reading now.
Figure 5-12. Testing voltage output with the DVA tester.
To test the charge-coil output you should set your voltmeter to a scale that will read as much as about 400 volts. Typical readings at cranking speed for charge coils are between 150 and 275 volts. You must check the workshop manual for your engine to get the exact specification for this.
Next, plug the meter leads into the socket or connect to the leads coming from the charge coil. Again, your manual will help you identify these two wires. Next crank the engine over, or use the pull cord and take a reading from your meter. If the reading you get is within specifications, your charge coil has tested fully okay and is not the source of any ignition problems.
Next test the sensor coil following the same procedure as for the charge coil, only for this coil you must switch to a low volt reading—20 volts or less. Typical sensor-coil output readings will be between 1.2 and 9 volts at cranking speed. Again, verify the specification in your engine's manual. Make sure to check all the sensor coils if your engine is equipped with more than one.
Next, you can test the ignition module's output to each of the high-tension coils using the meter and DVA adapter. For this test it's important to be sure the ground wire for your ignition module is secure, as damage to the module could occur if it is not.
Once you've located this ground wire you can attach to it the black lead from your multimeter/DVA combination. Also, it's a good idea to use your wiring diagram to locate the stop-circuit ground lead for your ignition module. Disconnect it from the stop circuit. This will isolate the ignition module from that circuit, and eliminate the possibility of a defect in the stop circuit leading you to misdiagnose your ignition module as faulty.
Next, switch your meter to a scale capable of reading as much as about 400 volts. Locate the high-tension coil primary feed wire (the wire that connects from the ignition module to the coil), attach your meter's red lead to the terminal point at the high-tension coil where this wire is attached, and crank over the engine. Your reading here, which will be somewhere between 150 and 350 volts, is the output voltage from the capacitor inside the ignition module. Match your reading to factory specifications for your engine. Perform this test for each ignition module output lead on your engine. You readings should be approximately the same for each lead on your module. If you discover a lead with no output, or a considerably lower output (check your engine's tolerance in the workshop manual), the ignition module is defective and must be replaced.
In some of the latest CD ignition systems, the ignition module is under the flywheel, and the sensor coils have been integrated with the module pack. In this case, you won't be able to touch the charge coil wiring, and you won't find any reference to sensor-coil testing in your workshop manual. The flywheel must be removed to service these components on this type of system. If your engine is like this, and your tests on the plugs, secondary wiring, and high-tension coils lead you to this point, you will need the services of your dealer.
I should emphasize that problems with charge coils, sensor coils, and the permanent magnets under the flywheel are extremely rare. You shouldn't ever have to deal with them on your engine. The only thing that classically causes early failure of these components is lack of early attention when an engine has been accidentally submerged in salt water. This saltwater exposure induces excessive corrosion, resulting in resistance to the electrical flow and premature failure. The correct procedures for handling a saltwater dunking are outlined in Chapter 10.
Let's pause here for a moment before we tackle the final tests of the ignition system. At this stage, you know how to verify your system's spark output with a seven-dollar tester. You know how to remove spark plugs, check them, and replace them. You know how to check the plug wires and the high-tension coils. You should also be able to check your charge and sensor coils with the help of your workshop manual. So what's left, you ask? What else could possibly cause ignition trouble? Well, there are a few things you might have to investigate one day. Your engine's stop circuit is one of them. And then there's timing. Finally, your ignition module may have some additional functions you'll need to look at. Let's take one thing at a time:
Your engine may have a remote key switch to turn the ignition on and off. Or, if it's a smaller engine, it may have a simple stop button mounted directly on the engine or steering tiller. In either case, the tool of choice for testing the circuit will be your ohmmeter. In addition, of course, you'll need the wiring diagram for your engine.
If you don't have a remote-control ignition switch, you'll need to begin your search under the engine cowl at the point where the wiring and cable controls exit the steering tiller assembly. One lead goes to a good engine ground, and the other goes to the ignition module. Verify that you have the correct wires by checking your engine-wiring diagram.
Install the emergency stop clip if your engine is so equipped. Your engine should now be in the run mode. Now find a good ground point on your engine and with your meter's black lead attached to ground, install the red lead in the plug assembly or attach it to the previously identified wire coming from the stop button.
Your meter should give you a high (infinity) reading indicating an open circuit if all is well. Any reading showing continuity indicates the switch is defective, or the wire coming from the switch is shorted to ground somewhere inside your tiller handle. In either case, you'll have to replace the assembly.
If all appears okay to this point, push the stop button in and check your meter; it should show a low reading, indicating continuity. Finally, if equipped, pull the clip out and observe your meter reading; the meter should show a low reading again. If pushing the stop button or pulling the emergency clip does not give the desired low ohmmeter reading, the assembly must be replaced. Figure 5-13 shows a typical meter hookup for these tests.
On larger engines, you will still be checking switch function and for short circuits to ground. In this case you'll just have a little more distance to cover—the distance between your engine's powerhead and the key switch itself. Again, you will use your ohmmeter and need your engine's wiring diagram.
For these tests you will need to positively identify all the terminal connections on the back of your key switch. To get to the switch, you may have to unfasten your assembly from the boat and remove the back cover of the control unit.
Figure 5-13. Testing the stop circuit.
Some good manuals give a detailed picture of the plug assembly coming from the back of this switch, and identify all the terminal connections. In that case, if you can reach the plug, you won't have to remove the remote-control assembly to perform these tests.
If you do have to remove the remote control unit and partially take it apart, be sure to follow your manual's instructions for opening up the control unit. In some cases, if you remove the central pivoting screw, you can inadvertently create a mess that will be a nightmare to reassemble. Be warned.
If the remote ignition switch is separate from the shift control, you shouldn't have a problem. Simply look for the back of the switch. You can usually get to it without removing the switch from the panel.
See your wiring diagram to identify the wire coming from the back of the ignition switch to the ground shut-off at the power pack. As with the smaller engines, this wire will usually terminate at a gang plug under the engine cowl in the harness going to the power pack. Once you're absolutely positive about its identity, disconnect the plug or connection to the module. Now you're ready for your ohmmeter tests. Start at the engine end.
First, connect the red test lead from your ohmmeter to the ignition-switch terminal that goes to the module. Connect your black test lead to a good engine ground. With the ignition key in the "on" position, your meter should give a high reading, infinity on the scale.
If your meter shows a complete circuit, indicated by a near 0 resistance reading, you must disconnect this same wire from the back of the ignition switch and check the meter reading again. If the meter now reads infinity, the ignition switch itself is faulty and must be replaced. If the meter indicates a complete circuit to ground, shown by little or no resistance on the gauge, then the wire that connects the ignition switch to the engine is shorted to ground and must be repaired.
If all of these readings check out okay, turn the key switch to the "off" position and check your meter. You should have a low resistance, reading near 0 ohms. If your meter still gives a reading of infinity, then you must check that the terminal and wire indicated by your engine wiring diagram as ground for the key switch are connected and in good condition. If they are, then you may have a break (open circuit) in the wire leading from the switch to the terminal on the engine. You'll have to check the entire length of this wire and either install a new one or splice the break. Figure 5-14 shows a typical wiring diagram for a remote-key installation, with the typical test points shown, and the possibly faulty wires indicated.
If after performing all of these tests to your engine's stop circuit(s) you still have a problem with your engine not shutting down with either the key switch or the stop button, then the only thing left in the circuit that could cause this fault is the ignition module itself. Unfortunately, it's a solid-state, completely sealed device, and you can't repair it in the field. You'll have to replace it.
Some midsize and larger outboards have a switch located in the trim/mounting bracket assembly. It's designed to cut out the ignition if the engine is trimmed too much and fails to pick up cooling water. Figure 5-15 shows this switch on a 70-hp Mercury outboard.
To test the tilt switch, remove the mounting screw that secures it to the engine. Disconnect the remaining lead coming from the switch. Now set your ohmmeter to the low ohms scale and hook it to the two switch leads. It doesn't matter which lead goes where.
Figure 5-14. Remote ignition switch installation.
Position the switch in your hand as it would normally be on the engine in the trim-down position. Observe the meter. It should read no continuity or infinity. Next, tilt the switch in your hand and tap its high end with a finger. The meter should now indicate continuity through the switch. If your test readings show anything else, replace the mercury switch.
I don't want to depress you, but it's possible to do a thorough test of all the ignition components we've mentioned, have everything check out okay electrically, and still not have a spark. Or, you may have a strong spark in an engine that backfires when you try to start it, or misfires at high speed. Your ignition system could still be the culprit. Before condemning the ignition module for either of these faults, let's verify a few facts.
First, you must be absolutely certain that all wires are hooked up correctly. It's all too easy to cross plug wires or switch primary feed wires going to the high-tension coils, so that the ignition module sends its signal
Figure 5-15. A mercury tilt switch.
to the wrong coil. Double-check everything with the help of your engine-wiring diagram. Gang-plug connections are always "keyed" so they can only fit together one way, but on engines with individual terminal connections, it's easy to make a mistake.
Also, make sure that all high-tension leads go back into their proper hold-down clamp on the engine, to avoid the possibility of a "crossfire" between cylinders.
Very rarely, the flywheel may be the culprit. Remember, it has carefully positioned magnets on its circumference. It's keyed to the engine's crankshaft so that these magnets pass by the appropriate charge or sensor coil at a carefully timed point in the engine's rotation.
On rare occasions (usually after the flywheel has been removed and improperly reinstalled) the flywheel may work loose on the end of the crankshaft and shear the positioning key. In this situation, the flywheel may "spin" independent of the crankshaft, altering the position of the magnets relative to the crankshaft position. The end result is an engine that is severely out of time.
To check for this, unplug the master plug to the ignition module to totally disable the ignition system. You don't want any risk of the engine starting with your hands on the flywheel. Next, grasp the flywheel firmly with both hands and feel for any movement from side to side or up and down, as shown in Figure 5-16.
Any evidence of movement indicates that the flywheel is loose on its mounting taper at the end of the crankshaft. The engine must be taken to an experienced mechanic. The flywheel must be removed, and the crankshaft and flywheel inspected, repaired, or replaced
Figure 5-16. Checking the flywheel for looseness.
as needed. With any luck, you will need only a new key.
If all the wiring is properly connected, and your flywheel is secure, then a timing check is in order. But you won't necessarily do it yourself. This is not a procedure for the inexperienced outboard engine mechanic to try.
First of all, there are different procedures for every outboard made. Secondly, for a precise job the ignition timing pointer position must be verified, and that requires special tools the average boat owner won't have. Lastly, the timing should be checked not only at idle, but for maximum advance at high speed. This is best done in a special test tank, or with the aid of a dynamometer specially designed for outboard engines. The average boat owner definitely doesn't have these tools.
Don't give up hope, though. If you're well equipped and reasonably experienced, you can set the timing by following the instructions in your workshop manual. Look for the section titled "Engine Synchronization and Timing," or something similar. On small, single-carburetor engines, the procedure is not especially complicated, and the timing could be set even by someone with limited experience. Just follow the instructions carefully. On large engines, though, I wouldn't recommend that you try it. The variables are many, and go beyond the scope of this book.
To sum up the section on timing, here are the important facts again:
• Timing will rarely change unless someone inadvertently alters the carburetor linkage or adjustments; or
• The flywheel comes loose from the crankshaft; or
• The flywheel magnets work loose on the underside of the flywheel—fairly common on some engines; or
• The engine has many hours on it, and the timing plate under the flywheel is worn and suffers from excessive play.
So, if no one has tried to "adjust" your carburetor, and the flywheel isn't loose, it's highly unlikely that your ignition timing has changed. But, if you have any doubts based on all the information presented here, have a professional look at your timing.
If your engine has been quitting intermittently, or suddenly losing speed, again on an intermittent basis, there is still a remote possibility that your ignition module (CDI unit) is acting up.
Unfortunately the ignition module is one component that may require you to rely on your dealer's expertise for some tests, particularly on midsize and large outboard engines. However, if your ignition problem was a lack of spark, and you have carefully performed all of the tests already outlined here, you can feel quite comfortable about purchasing a new module and installing it. That was your problem.
Other module-related problems are a little more difficult to pinpoint. Your module may incorporate a speed limiter. It could have a slow-down circuit designed to reduce revs if the engine overheats. If all your other tests point to the CD module (in anything other than a no-spark situation) inform your dealer of everything you have done, and rely on his advice about whether to replace the module. Remember, dealers will not accept returns on electrical components, so trial-and-error methods of testing can be expensive.
If you own a midsize or large outboard engine made within the last several years, you may have an additional sub-system integrated into your CD ignition called Optical Timing. This is a very sophisticated system designed to electronically control timing advance and retard functions for easier starting and to control the timing with absolute precision.
Once again, unfortunately, this system requires a full arsenal of specialized test equipment and adapters to troubleshoot. If your engine is equipped with a system of this type, I can only advise you to consult your dealer for diagnosis if your problem search goes beyond checking fuses, corroded or loose connections, spark plugs, plug wires, and coils as described earlier in this chapter.
To sum up this chapter, just remember these important facts. In most cases, problems with ignition systems will be visible: a broken wire, a corroded connection, or simply a bad spark plug that should have been replaced long ago.
Because there are many engine manufacturers and many different ignition systems, you must use this book in conjunction with the right service manual for your engine.
When you follow the guidelines in this chapter, and the simplified test procedures, you'll be able to pinpoint all common ignition system problems (and some that aren't so common) and make the necessary repairs.
If your testing leads you to something that must be handled by the dealer, console yourself with the thought that you'll have saved a lot of labor dollars by doing the diagnostic tests yourself.
