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Tech Tips
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Honda
Honda Ignition Diagnostics
Edited from an article by Gary E. Goms, ImportCar, March 2001
The very number of Honda distributor ignition system designs on the market can be intimidating. If we thumb through a shop manual, it appears that Honda has engineered a unique ignition system for each vehicle model and engine application. In addition, Honda ignition systems seem to experience repeat failures that seem to defy an import technician’s best diagnostic efforts.
Despite this apparent diversity, each Honda ignition system shares the same basic operating principles. With that in mind, it’s important to understand that the vast majority of Honda ignition failures can be diagnosed within a few minutes by using several basic diagnostic techniques requiring the use of a lab scope. In the following text, I will begin with a slightly different view of ignition basics, which we will later apply to diagnosing Honda ignition system failures. In addition, we’ll discuss how basic lab scope waveform and current ramping techniques can be used to simplify Honda ignition system diagnosis.
FORGOTTEN FUNDAMENTALS
Analyzing an electrical schematic of a modern Honda ignition system (or any other nameplate, for that matter) can become very confusing unless we remember how a basic ignition system creates a high-voltage spark and what additional functions are required to make a modern fuel-injected engine perform correctly.
To simplify the concept of how an ignition system operates, let’s begin with the old yet familiar contact-point ignition system such as those used on Honda Civics in the 1970s. To begin with, any ignition system must multiply a base or B+ voltage of, let’s say, 14.2 volts into a voltage with a high enough potential to cross an air gap of .030 inches under cylinder pressures exceeding 150-200 psi. Generally speaking, the early ignition systems must multiply the voltage in the B+ circuit by at least 1,000 times or to 14,200 volts so that the spark plug can initiate the combustion process between the air and gasoline being compressed in the engine’s cylinders.
The foundation of an ignition coil is an electromagnet that is created by winding insulated copper wire around a soft iron bar. When electricity flows through these primary windings, a strong magnetic field is created. When the electromagnet is turned off, the field collapses.
Up to this point, low-voltage, high-amperage B+ primary current hasn’t been converted into high-voltage, low-amperage secondary current. To accomplish this, engineers surround the electromagnet with a second (or secondary) winding having many more turns of wire than does the primary winding. When the electromagnet is turned off, the collapsing magnetic field of the primary circuit is "cut" by many thousands of secondary windings in the secondary circuit. Each time the magnetic field is cut by a secondary winding, voltage increases and amperage decreases. This assembly of iron core and primary/secondary windings is what we call an ignition coil.
Of course, we have to delve into the field of electrical engineering to fully explain how the simple electromagnet multiples voltage. Many design variations have taken place over the years, including placing the iron core on the outside of the windings to form what we now call an "e-core" coil design.
In addition, modern technology now insulates each wire in the coil through a complicated process of forcing epoxy into the windings. So we’ve progressed from simple oil-filled coils to solid epoxy-filled coils. In addition, engineers have found ways to make coils multiply voltage much more efficiently than in years past. The outcome, of course, is that we have many, many variations in coil design that require slightly different diagnostic interpretations when we apply advanced techniques such as current ramping and waveform analysis to test a modern ignition coil.
TRIGGERING FUNCTIONS
In earlier years, a cam-operated set of mechanical contact points was used to draw current through the primary windings of the ignition coil by grounding the primary circuit. The amperage drawn through the primary windings of the electromagnet would be limited to about 3 or 4 amperes by a resistor located in the primary circuit to prevent the contact points from overheating and oxidizing.
In later years, electronic ignition systems began using a power transistor to switch the primary current on and off. The primary current was limited by changing the amount of time (dwell angle) the primary current was drawn to ground or by electronically limiting the amount of current flowing through the primary circuit. The result is a more precise, durable and capable ignition system because the power transistor is able to operate at higher amperages (typically 7 amps) and thus generate higher secondary voltages without overheating the primary and secondary circuits. This allows engineers to design ignition systems that generate as high as 50,000 volts to jump wider spark plug gaps that, in turn, create a more consistent "burn" in the combustion chamber.
TIMING FUNCTIONS
Whereas the old contact-point systems were triggered by a cam mounted on a rotating distributor shaft, transistor or electronic ignition systems are triggered by a reluctor mounted on the distributor shaft. As the reluctor teeth pass by a magnetic pickup coil, a small alternating current is in the pickup coil. The current generated by the magnetic pickup coil signals the ignition module to turn on the power transistor.
Since the power stroke occurs only once each two revolutions on a four-cycle engine, the distributor is driven at one-half crankshaft speed so that the triggering of the primary coil winding occurs only at top dead center (TDC) on the compression stroke. With a low-amperage contact-point system, this strategy allows more dwell angle or saturation time to occur in the coil windings. In this way, a higher voltage can be developed in the secondary windings of the ignition coil. Practically all distributor-type ignition systems such as those used by Honda follow the practice of saturating the coil windings once per each compression stroke.
Keep in mind that a conventional distributor also times the spark to occur slightly before or at TDC on each cylinder compression stroke. The actual timing of each spark to each cylinder in the firing order is accomplished by the distributor rotor aligning with a contact inside the distributor cap.
Before we leave early-model distributors, let’s not forget that a centrifugal-style spark advance is used to add spark timing advance as the engine speeds up. A single or dual vacuum advance is used to add or subtract spark advance according to engine load as indicated by intake manifold vacuum. This system, if you will, is a mechanical computer that advances or retards the spark according to a very narrow set of operating conditions and standards.
COMPUTERIZATION
 Let’s fast-forward to multi-port, computer-controlled electronic fuel injection and computer-controlled spark advance systems like those found on modern Honda engines. Obviously, the engine computer or PCM processes electrical inputs such as crankshaft and camshaft position into electrical outputs like a timing signal for the fuel injection and ignition. To match fuel injector pulse and spark advance to varying engine speeds and loads, the PCM must receive a timing signal from the distributor that provides a base timing signal for both crankshaft and camshaft position.
Honda typically incorporates three sensors into the distributor that indicate crankshaft position (CKP), top dead center (TDC) and cylinder (CYL) position. In contrast to requirements for a computerized engine, a conventional distributor simply indicates when each of the four pistons is approaching TDC.
While dual-point throttle-body systems don’t require a #1 reference to time the fuel injection, multi-point fuel injection does require a CYL input to trigger the fuel injectors at a specific point, before the intake valve opens and the piston descends upon its intake stroke.
CKP, CMP AND CYL SIGNALS
At this point, we’re going to begin where the recommended service procedures leave off. Most service literature illustrates using a digital volt ohmmeter to measure resistance and voltage in a circuit. Clearly, the coil must have B+ power before it can generate a spark. Clearly, too, the battery must be fully charged before it will deliver adequate ignition voltage (at least 10 volts) during cranking.
But testing ignition circuits with an ohmmeter requires intrusive testing that may temporarily restore a poor electrical contact. In addition, since resistance testing is done with the system in an electrically unloaded condition, it doesn’t duplicate actual operating conditions. The net result is a diagnostic zero when, in fact, one or more of the distributor sensor circuits may become defective as the engine warms up. A change in temperature, for example, causes ignition coil and magnetic pickup windings to expand. In some cases, this expansion will create an open circuit if a wire happens to become cracked or broken.
So, the important objective in diagnosing ignition systems is to perform a non-intrusive test that leaves the ignition components undisturbed and measures electrical outputs as they occur in a normal operating environment. The minute the distributor cap is removed on a Honda, the CKP, CMP and CYL pickup connections can be disturbed. So let’s begin testing the vehicle in the same condition as it arrived on the shop floor.
SPARK/NO SPARK
The first question, of course, is do we have spark, no spark or intermittent spark? First of all, it’s important to test the battery condition. A battery must maintain at least 10 volts during cranking to maintain adequate B+ voltage at the ignition coil B+ terminal. Second, adequate B+ voltage must be maintained at the ignition switch or fuse box. A quick system voltage test can be performed by plugging in an aftermarket or home-made connector in the cigarette lighter or auxiliary power outlet socket. This way, system voltage can be quickly tested while cranking the engine from the driver’s seat.
Second, let’s begin a systematic spark test. Begin by alternately installing an adjustable spark tester on each spark plug wire. Several years ago, I had a Honda Civic with two open-circuited spark plug wires come into the shop. The previous shop had tested spark at only one wire and had assumed the ignition was defective. If the spark is weak or nonexistent at the spark plug, test at the coil lead on the distributor cap. If the spark is a white-blue arc at least 1/4" long at the coil lead, the Honda probably suffers from a spark perforation at the rotor. A perforation usually develops when firing voltage is drastically increased by worn spark plugs and open-circuit or high-resistance plug wires. In other cases, the lack of dielectric strength in a cheap distributor rotor may cause a similar failure. In any case, it’s just good preventive maintenance to replace suspect caps, rotors, wires and spark plugs.
LAB SCOPE DIAGNOSTICS
If we have a no-spark or intermittent spark condition at the distributor coil lead, our next step is to test the B+, CKP, CMP and CYL waveform outputs from the distributor. A lab scope display is superior to conventional testing because it provides a dynamic display of each signal.
If you’re not presently using a lab scope, let me briefly note that basic scopes are available for under $1,000 from one of several companies specializing in automotive electronic diagnostic equipment. A new basic scope available from retail sources may sell for about $1,300. When you learn the ropes of scopes, so to speak, you may want to move up into more expensive automotive scopes ($6,000) equipped with comprehensive ignition testing systems, or into one of several industrial models ($2,000-$3000) preferred by many master diagnostic techs. In any case, it’s time to get into the business of operating a lab scope.
WAVEFORM ANALYSIS
To begin a waveform analysis, you’ll need an engine management system wiring schematic for the specific Honda ignition system that you’re trying to diagnose. The best place to access the wiring harness is at the distributor connector. If you must tap directly into the wires, clean them with brake/electrical cleaner to remove grease and make the color coding more identifiable. Never scrape the insulation away from the wire, since this may allow moisture to destroy circuit integrity. Instead, use a professional pin-piercing probe to tap through the insulation. After testing is completed, the insulation puncture should be sealed with a commercial ignition sealer.
As for testing, B+ voltage can be evaluated with a lab scope (See Photo 8). In this case, the amplitude is set at 10v per division and the waveform shows 12.5 volts available to the distributor. Next, the crank sensor waveform (CKP) displays a 10-volt alternating current, KOER (See Photo 3). Keep in mind that any voltage generated by a magnetic pickup will be less with the engine cranking. As a rule of thumb, the signal should be identifiable and should be at least 25% of the KOER or idle value.
Next, we’ll look at the TDC sensor (See Photo 4), the CYL sensor (See Photo 5) and the TACH signal (See Photo 7). Notice that the TDC (See Photo 4) is pulsing approximately four times faster than the CYL sensor (See Photo 5). The tach signal (See Photo 7) indicates that the module is triggering the primary coil winding. This indicates that the module is operating correctly.
These waveforms are from a known good (new) distributor on a 1992 Acura Integra. Although we might have some waveform variation from model to model and from lab scope to lab scope, the basic waveform should be present with no prominent glitches.
Last, a square-wave signal should be returning from the PCM to the distributor ignition module. Remember that in a computer-controlled engine, the PCM usually controls the spark advance. If the three inputs (CKP, CMP and CYL) are reaching the PCM, then the PCM should be returning a square-wave timing signal similar to Photo 6. If the PCM is returning a square-wave signal, then the three sensors located in the base of the distributor are functioning correctly.
IGNITION COIL DIAGNOSIS
I mentioned previously that there are many different ways of building an ignition coil. This very fact makes traditional secondary waveform analysis more difficult since the waveform may vary from system to system.
While space doesn’t allow me to discuss the subject in detail, the most accurate method of analyzing the condition of an ignition coil is to display current primary draw on a lab scope by using a low-ampere inductive probe. This type of diagnostic method displays the current rise in the coil windings, current limiting and the interruption of current at the end of the saturation cycle. Of course, we will see some different current ramps for different types of coils. But the basic current ramp waveform will display an angular, straight-line ramp to the point of current limiting. The opening of the primary circuit by the ignition module should be represented by a straight-line drop to zero amperage.
Current ramping isn’t a complex procedure, but it does help to have a manual that helps you interpret variations in waveform patterns. One of several automotive electronics specialty firms can supply the manuals and current ramping equipment at a very reasonable cost. Current ramping is becoming a more important tool than ever for diagnosing shorted coil windings in Honda ignition systems, so do a little research on training materials and equipment. It’ll pay off in the long run.
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