See Figure 1
During the years 1975 through 1977, all American Motors built engines were equipped with the Breakerless Inductive Discharge (BID) ignition system. The system consists of an electronic ignition control unit, a standard type ignition coil, a distributor that contains an electronic sensor and trigger wheel instead of a cam, breaker points and condenser, and the usual high tension wires and spark plugs. There are no contacting (and thus wearing) surfaces between the trigger wheel and the sensor. The dwell angle remains the same and never requires adjustment. The dwell angle is determined by the control unit and the angle between the trigger wheel spokes.
See Figure 2
The AMC Breakerless Inductive Discharge (BID) ignition system consists of five components:
The control unit is a solid state, epoxy sealed module with waterproof connectors. The control unit has a built-in current regulator, so no separate ballast resistor or resistance wire is needed in the primary circuit. Battery voltage is supplied to the ignition coil positive (+) terminal when the ignition key is turned to the ON or START position; low voltage coil primary current is also supplied by the control unit.
In place of the points, cam, and condenser, the distributor has a sensor and trigger wheel. The sensor is a small coil which generates an electromagnetic field when excited by the oscillator in the control unit. This system was last used in 1977.
When the ignition switch is turned ON, the control unit is activated. The control unit then sends an oscillating signal to the sensor, which cause the sensor to generate a magnetic field. When one of the trigger wheel teeth enters this field, the strength of the oscillation in the sensor is reduced. One the strength drops to a predetermined level, a demodulator circuit operates the control unit's switching transistor. The switching transistor is wired in series with the coil primary circuit; it switches the circuit off, inducing high voltage in the coil secondary winding when it gets the demodulator signal. From this point on, the BID ignition system works in the same manner as a conventional system.
- Check all the BID ignition system electrical connections.
- Disconnect the coil-to-distributor high tension lead from the distributor cap.
- Using insulated pliers and a heavy glove, hold the end of the lead 1 / 2 in. away from a ground. Crank the engine. If there is a spark, the trouble is not in the ignition system. Check the distributor cap, rotor, and wires.
- Replace the spark plug lead. Turn the ignition switch OFF and disconnect the coil high tension cable from the center tower on the distributor cap. Place a paper clip around the cable 1 / 2 - 3 / 4 in. from the metal end. Ground the paper clip to the engine. Crank the engine. If there is spark, the distributor cap or rotor may be at fault.
- Turn the ignition switch OFF and replace the coil wire. Make the spark test of Step 3 again. If there is no spark, check the coil high tension wire with an ohmmeter. It should show 5-10,000 ohms resistance. If not, replace it and repeat the spark test.
- Detach the distributor sensor lead wire plug. Check the wire connector by trying a no. 16 (0.177 in.) drill bit for a snug fit in the female terminals. Apply a light coat of Silicone Dielectric Compound or its equivalent to the male terminals. Fill the female cavities 1 / 4 full. Reconnect the plug.
- Repeat the test of Step 4.
- If there was a spark in Step 7, detach the sensor lead plug and try a replacement sensor. Try the test again. If there is a spark, the sensor was defective.
- Connect a multitester with a volt scale, between the coil positive terminal and an engine ground. With the ignition switch ON, the volt scale should read battery voltage. If it is lower, there is a high resistance between the battery (through the ignition switch) and the coil.
- Connect the multitester between the coil negative terminal and an engine ground. With the ignition switch ON, the voltage should be 5-8v. If not, replace the coil. If you get a battery voltage reading, crank the engine slightly to move the trigger wheel tooth away from the sensor; voltage should drop to 5-8v.
- Check the sensor resistance by connecting an ohmmeter to its leads. Resistance should be 1.6-2.4 ohms.
Test the coil with a conventional coil checker or an ohmmeter. Primary resistance should be 1.25-1.40 ohms and secondary resistance should be 9-12K ohms. The open output circuit should be more than 20 kilovolts. Replace the coil if it doesn't meet specifications.
See Figures 3 through 10
If you must remove the sensor from the distributor for any reason, it will be necessary to have the special sensor positioning gauge in order to align it properly during installation.
- Scribe matchmarks on the distributor housing, rotor, and engine block. Disconnect the leads and vacuum lines from the distributor. Remove the distributor. Unless the cap is to be replaced, leave it connected to the spark plug cables and position it out of the way.
- Remove the rotor and dust cap.
- Place a small gear puller over the trigger wheel, so that its jaws grip the inner shoulders of the wheel and not its arms. Place a thick washer between the gear puller and the distributor shaft to act as a spacer; do not press against the smaller inner shaft.
- Loosen the sensor hold-down screw with a small pair of needlenosed pliers; it has a tamper proof head. Pull the sensor lead grommet out of the distributor body and pull out the leads from around the spring pivot pin.
- Release the sensor securing spring by lifting it. Make sure that it clears the leads. Slide the sensor off the bracket. Remember, a special gauge is required for sensor installation.
- Remove the vacuum advance unit securing screw. Slide the vacuum unit out of the distributor. Remove it only if it is to be replaced.
- Clean the vacuum unit and sensor brackets. Lubrication of these parts is not necessary.
- Install the vacuum unit, if it was removed.
- Assemble the sensor, sensor guide, flat washer, and retaining screw. Tighten the screw only far enough to keep the assembly together; don't allow the screw to project below the bottom of the sensor.
Replacement sensors come with a slotted head screw to aid in assembly. If the original sensor is being used, replace the tamperproof screw with a conventional one. Use the original washer.
- Secure the sensor on the vacuum advance unit bracket, making sure that the tip of the sensor is placed in the notch on the summing bar.
- Position the spring on the sensor and route the leads around the spring pivot pin. Fit the sensor lead grommet into the slot on the distributor body. Be sure that the lead can't get caught in the trigger wheel.
- Place the special sensor positioning gauge over the distributor shaft, so that the flat on the shaft is against the large notch on the gauge. Move the sensor until the sensor core fits into the small notch on the gauge. Tighten the sensor securing screw with the gauge in place (through the round hole in the gauge).
- It should be possible to remove and install the gauge without any side movement of the sensor. Check this and remove the gauge.
- Position the trigger wheel on the shaft. Check to see that the sensor core is centered between the trigger wheel legs and that the legs don't touch the core.
- Bend a piece of 0.050 in. gauge wire, so that it has a 90º angle and one leg 1 / 2 in. long. Use the gauge to measure the clearance between the trigger wheel legs and the sensor boss. Press the trigger wheel on the shaft until it just touches the gauge. Support the shaft during this operation.
- Place 3 to 5 drops of SAE 20 oil on the felt lubricator wick.
- Install the dust shield and rotor on the shaft.
- Install the distributor on the engine using the matchmarks made during removal and adjust the timing. Use a new distributor mounting gasket.