stays at zero or near zero, conduct the following three checks to locate the source of trouble:
Check the current flow at the distributor. Disconnect the distributor primary wire from the top of the coil. Take a voltmeter reading from the distributor terminal of the coil. Current should flow through the circuit.
Check the opening and closing of the breaker points. If not adjusted properly, they may not open and close. Also look for a mechanical failure of the points or cam. Lubricate the rubbing block at this time if necessary.
Check grounding of the movable breaker point, the stud at the primary distributor wire terminal, or the wire of the condenser (pigtail). None of these should be grounded.
Secondary Circuit Tests
The high voltage in the secondary circuit is produced by the ignition coil. Current flows out of the coil at the secondary terminal through a cable to the distributor cap and rotor. The rotor distributes the current through the cap and cables to the spark plugs, and then to ground. The checkpoints for the secondary circuit are the secondary terminal of the coil, the coil-to-distributor cap cable, the distributor cap, rotor, spark plug cables, and spark plugs.
You should conduct the secondary circuit check as follows:
1. Pull the coil high-voltage cable from the distributor cap and hold the loose end of the cable about one-fourth of an inch from a good grounding point on the engine block.
2. Crank the engine and look for a spark to bridge the gap between the loose end of the cable and the grounding point. If you see a blue spark proceed to the next step since the coil is functioning normally. If you see a yellow spark or no spark at all, the trouble sources are in the primary circuit, the coil, and the coil-to-distributor cable.
3. Remove the sparkplug cables from sparkplugs and lift the distributor cap off. Connect one ohmmeter test lead to a spark plug cable connector and the other test lead to the terminal inside the distributor cap for the spark plug cable. Measure the resistance of the other spark plug cables in turn. Cable resistance should not exceed the manufacturer's recommendations. Excessive resistance can result from cable damage, defective spark plug connector, corroded distributor cap tower, or unseated cable in the tower.
4. Inspect the distributor cap inside and out for carbon tracking cracks, and inspect it for a worn center contact button or burned spark plug cable contacts.
5. Remove the rotor and inspect it. Look for high-resistance carbon, a burned tip, or a grounded rotor.
Because of the difference in materials and quality control used by manufacturers of distributor caps and rotors, you should use both items from the same manufacturer.
6. Remove all spark plugs from the engine and inspect each one. Look for fouled plug tips, gaps that are too wide or bridged, chipped insulators, and other conditions that can cause high resistance at the electrodes.
Coil Resistance Tests
You can use a simple ohmmeter to check the resistance of the ignition coil. Its primary circuit and secondary circuit are tested separately. To check the primary side, connect the ohmmeter leads across the primary terminals of the coil. Use the low ohms scale of the meter. The resistance should be about 1 ohm for coils requiring external ballast resistors and about 4 ohms for coils not requiring the ballast resistors. In checking the secondary side, switch to the high scale of the ohmmeter. Connect one ohmmeter lead to the distributor cap end of the coil secondary wire and the other lead to the distributor terminal of the coil. The condition of the coil is satisfactory if the meter reading is between 4,000 and 8,000 ohms, although the resistance of some special coils may be as high as 13,000 ohms. Should the reading be a lot less than 4,000 ohms, the secondary turns of the coil are probably shortened. A reading of 40,000 ohms or more indicates an open secondary, a bad connection at the coil terminal, or a high resistance in the cable.
The preceding techniques for troubleshooting a conventional battery/coil ignition system also apply, for the most part, to troubleshooting the basic types of transistorized ignition systems: breaker-point type and breakerless. Special techniques, however, are used in checking the electronic components of a transistorized ignition system. Before testing any electronic ignitionContinue Reading