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Old 07-25-2004, 07:30 PM
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Ignition system info................

I copied this information from the AIC (Automotive Information Center) website. Thanks to them.

Breaker Point Systems
Although all domestic cars have been built with electronic ignition since 1975, I'll still provide some basic information on point type ignition in case you like to work on vintage automobiles -- or, tractors, marine engines, etc. First, you should be aware that the spark occurs when the points OPEN -- that's when the primary field collapses, inducing high voltage in the secondary windings of the coil. Next, remember that there should be zero ohms between the points when they're closed, and there must be infinite resistance between the hot point and ground with the points open.
Dwell is the percentage of time the points are closed, and is thus a function of the breaker point gap. You can check dwell with your meter's red lead attached to the coil's negative terminal, and the other lead to ground. The smaller the point gap, the larger the dwell reading.
A DMA (Digital Mullet-Meter) can easily test ignition condensers/capacitors. Select the Ohms function, touch one lead to the pigtail and the other to the case, and you should see resistance rise from zero to infinity as the meter's battery charges the condenser. No other reading is acceptable. Check both ways.
Residence of induction
Whether point type or electronic, the magic of induction, which causes that high-voltage discharge at the spark plugs, still resides in the coil. For some reason, a bad coil is often overlooked as the cause of a nostart, but you can check it easily with a DMM or an ordinary analog ohmmeter. Primary winding resistance as measured between the plus and minus terminals is typically between a one half ohm and a few ohms. Secondary resistance (measured between the negative primary terminal and the high tension terminal) will generally range from 2,000 to 15,000 ohms. Tests should be done with the coil cold, then hot.

Electronic Ignition Principles and Diagnosis
In the early days of the automobile, numerous methods of setting fire to that compressed charge in an engine's cylinders were tried. Platinum tubes heated red hot by an external flame were mounted in the combustion chambers, and low tension ignition produced an arc between two contacts when they were moved apart mechanically. But undoubtedly the most primitive and amazing idea was the flint and steel sparking arrangement a rough piece of steel was welded to the top of the piston, and this rubbed against a spring loaded flint. Magnetos and trembler coils, such as found on the Ford Model T, were great improvements.
But the Kettering breaker point/condenser/coil system, which appeared in 1911, became the universal standard, eventually supplanting the magneto. It was simple, dependable, and easy to service. It did, however, have drawbacks. The points' contact surfaces eroded and burned eventually, rpm capability was limited by the tendency of the moving point to float from inertia, dwell decreased and spark weakened with speed, and, perhaps most important, spark timing retarded from its original setting as the moveable point's rubbing block wore against the distributor cam. Especially in the U.S. where car makers had to certify that their products would meet government emissions standards for long periods, such timing variation could not be tolerated.
Applied electronics
This was a logical application for electronics. Instead of having a wear-prone and super-sensitive mechanical switch control the flow of current to the primary winding of the coil, transistors were used. These semiconductor devices have the ability to switch a relatively large amount of amperage when they receive a very small control signal current, they are for all practical purposes capable of doing this at any speed, and they don't wear or erode.
The various breakerless electronic ignition system designs differ in the way the transistor control signal current is produced. The earliest was the magnetic pickup type, in which a reluctor or armature having as many teeth as there are cylinders in the engine rotates past a fixed magnet and pickup coil. As each tooth passes the pickup, it generates an electrical impulse (this is similar to an alternator without diodes). The transistor in the control module, also known as the igniter, switches the ignition coil's primary circuit on and off according to this impulse. This principle was the basis of the 1973 Chrysler Corporation system, the first electronic ignition offered as original equipment. It is still widely used on many makes today.
The Hall Effect type is also popular. The Hall principle states that if a constant current flows through a thin conducting material, and that material is exposed to a magnetic field, voltage will be generated, and the amount of voltage will depend on the strength of the field.
In an ignition system, this phenomenon is put to work by the action of a shutter wheel in the distributor that interrupts the field created within the Hall generator by a permanent magnet (this is mounted across an air gap from a magnetically conducting element with a thin semiconductor layer). The wheel has as many shutters as there are cylinders, and they can be compared to the flat spots on a distributor cam. The ignition control unit is designed to supply current to the coil's primary winding while the shutter wheel is blocking the field. When the shutter moves out of the way and Hall voltage is produced, the control unit cuts off primary circuit current, the coil's field collapses, and induction produces high voltage in the secondary winding.
There are other types too, such as optical triggers, but the magnetic pickup and Hall Effect varieties are the most common. Also, late model ignition systems often include features such as electronic spark advance controls that make vacuum and centrifugal mechanisms less important or entirely unnecessary, and a detonation sensor, a piezoelectric crystal bolted to the engine that generates a tiny voltage signal when it "hears" the particular frequency of spark knock (the control unit responds by retarding ignition timing). But those are subjects for other sections in this encyclopedia. Here, I'll concentrate on the parts that cause spark to be created.
Not failure free
Although electronic ignition is extremely dependable, failures do occur, mostly in the form of nostarts. Whenever you are presented with a car that refuses to fire up, the thing to look for first is spark, just as you did with conventional ignition. Pull the coil wire out of the cap, hold it about 1/8 in. from ground (too big a gap will make the system go to maximum voltage, and in some designs this has been known to damage the electronic components or the coil), or use one of those convenient testers -- basically a spark plug with a ground clip welded to it -- and crank the engine.
Be careful not to jump to conclusions here. If you don't see a robust discharge of voltage, it doesn't necessarily mean the ignition system is at fault. Control modules or distributor pickups are sometimes mistakenly replaced when the problem is actually a snapped OHC belt or broken timing chain. After all, the distributor shaft has got to turn. So, as you activate the starter, look down the oil filler hole at the camshaft or rocker arms, or remove the distributor cap and watch for rotor movement.
If you find spark at the coil wire, yet the engine won't start, it's possible that ignition is not occurring at the right time. Perhaps the camshaft, distributor drive, or rotor has jumped from its proper position. Or, maybe someone has installed the distributor incorrectly, or even mixed up the order of the spark plug wires. If rotor position and firing order check out okay, remember that fouled spark plugs are a frequent cause of nostarts, so remove and examine them. In cases where they're in good condition also, lack of ignition is not the problem. Either fuel supply or compression, the other two legs of the tripod that supports combustion, is at fault.
If, on the other hand, there was no evidence of high voltage during your spark test, the next step is to find out what component in the ignition primary circuit is causing the problem. While it would take a whole volume to include specific testing procedures for all the different electronic ignition systems in use, I can provide some checks that are generally applicable and will identify the problem in many cases.
Coil tests
As a preliminary, check the coil. Primary winding resistance is typically somewhere around one ohm, and that of the secondary (measured at the coil's high tension terminal) 2,000 to 15,000 ohms. There's also a direct method: With a test light, make sure current is available at the plus terminal of the coil with the ignition on. Connect a jumper wire with a capacitor spliced into it (.33 microfarad is ideal) between the minus terminal and ground, and hold the high tension lead near a convenient bolt or casting as in your initial spark test. Using a second jumper (also grounded), brush the negative terminal and look for spark.
Control module
On systems with external control modules, always make sure the module is properly grounded. On some Japanese cars, for instance, the wire that handles this is attached to the voltage regulator mounting bolt, and the connection sometimes corrodes to the point that the engine won't start. Regardless of the make of car, it's a good idea to use a jumper to provide an auxiliary ground, then try the spark test again before condemning anything.
On many designs, it's possible to test the control module by triggering it artificially. Remove the coil wire from the distributor cap and plug in a spark tester, or place it a short distance from a good ground, turn the ignition on, then hold the body of an electric drill or soldering gun against the distributor. If spark is produced when you run the drill or turn on the soldering gun (this simulates the control signal you may have to try several different positions), the module is good. Unfortunately, this isn't a comprehensive test because if you don't get spark, you can't be sure whether the module is at fault, or the positioning of the drill or soldering gun is simply not adequate. It's worth a try, however, because if you do generate spark, you'll know the control module is not the problem.
A basic check used with every system is to make sure the proper amount of voltage is available at the control unit. You'll have to use a service manual to find out which wire supplies the current.
Signal generator examination
Another test that's done universally on the magnetic pickup type is to measure the resistance of the pickup coil. Attach your ohmmeter across the two wires of the pickup, and check the reading against specifications. On a typical Toyota, for example, you should see between 140 and 180 ohms. If you get no resistance, the coil is shorted. If you get infinite resistance, it's open.
If you have a DMM (Digital Multi-Meter) with an analog scale, you can check a magnetic pickup by separating the distributor's plug, and attaching your DMM (set to low volts) across the two terminals that go to the pickup. You should see voltage pulses on the scale as you crank the engine.
The size of the air gap between the armature and pickup coil is important. To check it accurately against specifications, you'll have to use a brass feeler gauge to eliminate magnetic drag.
With Hall Effect, the procedure is different. To test, unplug the threeterminal connector, jump straight battery voltage to the power terminal of the pickup (that's the one that gets voltage with the key on), and ground the negative terminal. Attach your DMM (again, set to volts) between the signal output terminal and ground. Crank the engine or rotate the distributor so that none of the shutter blades is between the Hall Effect magnets, then move a feeler gauge in and out of the gap. You should see alternating 0 V and 12 V readings.
On most designs, you can bypass the Hall generator (also called the Hall sender) by triggering the control unit with a jumper. On a typical VW, for example, attach the coil wire to a spark tester, put a test light between coil terminal #1 and ground, remove the connector from the distributor, turn the ignition key on, then momentarily ground the center terminal of the distributor connector (green wire). If you get spark and the test light dims, the Hall generator is bad. If the light dims, but there's no spark, a new coil is needed. If neither happens, check for an open circuit between the control unit and the distributor. No fault in those wires means the control unit has failed.
Before condemning it, however, try one more test. Remove the connector from the distributor, attach the positive lead of your voltmeter to terminal #15 and the negative lead to #1 (both on the coil), then turn the ignition on. The needle should jump to six volts, then drop to zero within about two seconds. If it doesn't drop, a new control unit is required.
A few miscellaneous tips:
Never disconnect or connect any wires with the ignition on.
When doing a compression test, ground the coil wire so that a big gap doesn't cause the system to generate a potentially damaging amount of voltage.
Some designs, such as Ford's TFI, require a layer of special silicone grease between the module and its mounting surface. Without it, the module will overheat.
When you encounter a nostart in a Volkswagen equipped with an idle stabilizer, remove both connectors from the stabilizer unit, which you'll find under a plastic cover in the plenum at the back of the engine compartment (it's mounted on top of the control unit), and plug them together. Spark now means the stabilizer is bad or its connector pins are damaged (new pins are available). You could drive the car with this component bypassed, and, providing it doesn't have accessories that tend to drag idle speed down, the difference might never be noticed. But replacing the unit is the proper thing to do.
On systems with integral coil and distributor, such as GM's HEI, there's no separate coil wire, so you'll have to perform your engine cranking spark test at the end of a spark plug lead.
On Hall Effect systems with a combination rotor and shutter wheel that has a contact for grounding the unit to the distributor shaft (such as on a typical Chrysler product), make sure the contact and shaft are clean.
Direct ignition systems, as first seen on Saabs and GM's, have no distributor or spark plug wires, and are the next logical step in the evolution of ignition
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