See Figures 1 through 8
The electronic ignition system can be tested with either special ignition testers or a voltmeter with a 20,000 ohm/volt rating and an ohmmeter using a 9 volt battery as a power source. Since the special ignition system testers have manufacturer's instructions accompanying the units, the technician can refer to the procedural steps necessary to operate them. The following outline will cover the ohm/volt meter unit.
SECONDARY CIRCUIT TEST
- Remove the coil wire from the distributor cap and hold it cautiously about 1 / 4 " away from an engine ground, then crank the engine while checking for spark.
- If a good spark is present, slowly move the coil wire away from the engine and check for arcing at the coil while cranking.
- If good spark is present and it is not arcing at the coil, check the rest of the parts of the ignition system.
IGNITION SYSTEM STARTING TEST
- Visually inspect all secondary cables at the coil, distributor and spark plugs for cracks and tightness.
- Check the primary wire at the coil and ballast resistor for tightness.
- With a voltmeter, measure the voltage at the battery and to ascertain that enough current is available to operate the cranking and ignition systems.
- Remove the coil secondary wire from the distributor cap.
- With the key ON, use a jumper wire and momentarily touch the negative terminal of the coil to ground while holding the coil secondary wire approximately 1 / 4 " from a good engine ground. A spark should be observed.
- Verify the spark is getting to the spark plugs. If the spark plugs are being fired, the ignition system is not responsible for the engine not starting.
- If no spark is observed at the ignition coil wire, turn the ignition switch to the OFF position and disconnect the 10 way connector from the bottom of the spark control computer. Turn the ignition switch to the ON position and hold the ignition coil wire approximately 1 / 4 " away from a good engine ground.
- With battery current to the coil negative terminal, intermittantly short the terminal to ground. If spark now occurs, replace the spark control computer.
- If the voltage is incorrect, check the continuity of the wiring between the battery and the coil positive terminal. Repair the wiring as required and retest.
- Should battery voltage (within one volt) not be present at the coil negative terminal with the ignition key ON, replace the ignition coil.
- Should battery voltage (within one volt) be present, but no spark is obtained when shorting the negative terminal, replace the ignition coil.
- If spark is obtained, but the engine will still not start, turn the ignition switch to the RUN position and with the positive lead of the voltmeter, measure the voltage from cavity No. 1 to the ground lead of the disconnected lead from the computer. The voltage should be within 1 volt of the battery voltage noted earlier.
- If battery voltage is not present, check the wire for an open circuit and repair. Retest as required.
- Place a thin insulator between the curb idle adjusting screw and the carburetor switch or, make sure the curb idle adjusting screw is not touching the carburetor switch.
- Connect the negative voltmeter lead to a good engine ground. Turn the ignition switch to the RUN position and measure the voltage at the carburetor switch terminal. The voltage should be approximately 5 volts.
- If the voltage is not 5 volts, turn the ignition switch to the OFF position and disconnect the 10 way connector from the bottom of the spark control computer. Turn the ignition switch back to the RUN position and measure the voltage at terminal 2 of the connector.
- Voltage should be within 1 volt of battery voltage. If the correct voltage is not present, check the wiring between terminal 2 of the connector and the ignition switch for open or shorted circuits or poor connections.
- Turn the ignition switch to the OFF position and disconnect the connector from the bottom of the spark computer, if not already done. With an ohmmeter, check the continuity between terminal 7 of the connector and the carburetor switch terminal. Continuity should exist between these two points. If not, check for opens or poor connections.
- Check for continuity between terminal 10 of the connector and engine ground. If continuity exists, replace the Spark Control Computer assembly. If continuity does not exist, check the wiring for open circuits or poor connections. Repeat Step 18.
- If the engine still fails to start, turn the ignition switch to the OFF position and with an ohmmeter, measure the resistance between terminal 5 and terminal 9 for the start pick-up coil of the 10 way connector. The resistance should be between 150-900 ohms.
- If the resistance is not within the specified range, disconnect the Pick-up coil leads from the distributor. Measure the resistance at the lead going into the distributor. If the reading is now between 150-900 ohms, an open circuit or faulty connections exists between the distributor connector and terminals 5 and terminal 9 of the 10 way connector. If the resistance is not within specifications, the pick-up coil is bad. Replace it and set the air gap to specifications.
- Connect one lead of the ohmmeter to the engine ground and with the other lead, check for continuity at each terminal of the leads going to the distributor. There should be no continuity.
- If there is continuity, replace the pick-up coils. Adjust the air gap to specifications.
- Attempt to start the engine. If it fails to start, repeat the tests. If the engine still fails to start, replace the Spark Control Computer.
Should the engine still fail to start with the replaced Spark Control Computer, Chrysler Corp. suggests reinstalling the original Spark Control Computer and repeating the tests. However, proper testing of the circuits and pick-up should result in the engine starting, unless unrelated problems exist in the systems.
TESTING FOR POOR PERFORMANCE
Correct basic timing is essential for optimum engine performance. Before any testing and service is begun on a poor performance complaint, the basic timing must be checked and adjusted as required. Refer to the underhood specifications label for timing adjustment specifications.
Spark Computer Advance of Spark Control Computer Testing
Incorporated within the digital microprocessor electronics are programmed spark advance schedules which occur during cold engine operation. These programmed advance schedules have been added to reduce engine emissions and improve driveability. Because they will be changing at different engine operating temperatures during warm-up, all spark advance testing should be done with the engine at normal operating temperature and a temperature sensor that is connected and operating correctly.
- With an attached timing light, be sure basic timing is correctly adjusted.
- Place an insulator between the curb idle adjusting screw and the carburetor switch, or be sure the screw is not touching the switch.
- Remove tand plug the vacuum line at vacuum transducer.
- Connect an auxiliary vacuum source to the vacuum transducer and set the vacuum at 16 in.Hg (318 CID engines).
- Increase the engine speed to 2,000 rpm. Wait for approximately one minute or specified accumulator clock-up time and check the specifications. On certain systems with an accumulator, the specified time must be reached with the carburetor switch ungrounded before checking the specified spark advance schedule. This would be noted on the information specification label.
Advance specifications are in addition to basic timing.
- Should the computer fail to obtain specified specifications, the Spark Control Computer should be replaced. Perform the same test on the replacement computer.
Carburetor Switch Testing
Grounding the carburetor switch eliminates all spark advance on mosts systems.
- With the ignition key in the OFF position, disconnect the 10 way connector from the Spark Control Computer.
- With the throttle completely closed, check the continuity between pin 7 of the disconnected 10 way connector and a good engine ground.
- If no continuity exists, check the wires and the carburetor switch. Recheck the basic timing.
- With the throttle open, check the continuity between pin 7 of the disconnected 10 way connector harness connector and a good engine ground. There should be no continuity.
Engine Temperature Sensor TestingENGINE TEMPERATURE SWITCH (CHARGE TEMPERATURE AND COOLANT)
- Turn the ignition switch to the OFF position and disconnect the wire from the temperature switch.
- Connect one lead of an ohmmeter to a good ground on the engine, or in the case of the charge temperature switch, to its ground terminal.
- Connect the other lead of the ohmmeter to the center terminal of the coolant switch.
- Check for continuity using the following ohmmeter readings:
- Cold engine-The continuity should be present with a resistance less than 100 ohms. If not, replace the switch. The charge temperature switch must be cooler than 60°F in order to achieve this reading.
- Hot engine at normal operating temperature-The terminal reading should show no continuity. If it does, replace the coolant switch or the charge temperature switch.
- Connect the leads of an ohmmeter to the terminals of the sensor.
- With the engine cold and the ambient temperature less than 90°F., the resistance should be between 500-1100 ohms.
- With the engine at normal operating temperature, the resistance should be greater than 1300 ohms.
- If the resistance is not within the specified range, replace the sensor. The sensor will continually change its resistance with a change in engine operating temperature.
Detonation Sensor Testing
- Connect an adjustable timing light to the engine.
- Start the engine and run it on the second highest step of the fast idle cam (at least 1200 rpm).
- Connect an auxiliary vacuum supply to the vacuum transducer and set on 16 in.Hg.
- Tap lightly on the intake manifold near the sensor with a small metal object.
- Using the timing light, look for a decrease in the spark advance. The amount of decrease in the timing is directly proportional to the strength and frequency of the tapping. The most decrease in timing will be 11° for 1984 models and 20° for 1985 and later models.
- Turn the ignition switch to the OFF position. With the engine stopped, disconnect the timing light.
Electronic Exhaust Gas Recirculation System Testing
The Electronic EGR control is located within the electronic circuitry of the Spark Control Computer and its testing procedure is outlined.
- All the engine temperature sensors must be operating properly before the tests can be done.
- With the engine temperature cold and the ignition switch turned to the OFF position, connect one voltmeter lead to the gray wire on the EGR solenoid and the second to a good engine ground.
- Start the engine. The voltage should be less than one volt. It will remain at this level until the engine has reached its normal operating temperature range and the electronic EGR schedule has timed out. The solenoid will then de-energize and the voltmeter will read charging system voltage.
- If the charging system voltage is not obtained, replace the solenoid and repeat the test.
- If the voltmeter indicates charging system voltage before the EGR schedule is complete, replace the computer or the externally mounted timer.
The 318-2 Federal engines have no thermal delay below 60°F ambient temperature. It will follow the EGR time delay schedule only.
- If an engine is started with the temperature hot, the EGR solenoid will be energized for the length of the time delay schedule only. It will then de-energize.
Electronic Throttle Control System Testing
Incorporated within the Spark Control Computer is the electronic throttle system. A carburetor mounted solenoid is energized when the air conditioner, electric back light or the electric timers are activated. The two timers which are incorporated in the ignition electronics, operate when the throttle is closed, plus a time delay (2 seconds), or after an engine start condition.
- Connect a tachometer to the engine.
- Start the engine and run it until normal operating temperature is reached.
- Depress the accelerator and release it. A higher than curb idle speed should be seen on the tachometer for the length of the EGR schedule.
- On vehicles equipped with/and turning on the air conditioning or the back light, depressing the accelerator for a moment should give a higher than curb idle speed. Turning the air conditioning and Back light off will produce the normal idle speed.
With the air conditioning system on, the air conditioning clutch will cycle on and off. This should not be mistaken as a part of the electronic control system.
- If the speed increases do not occur, disconnect the three way connector at the carburetor.
- Check the solenoid with an ohmmeter by measuring the resistance from the terminal that contains the black wire to ground. The resistance should be between 15-35 ohms. If not within specifications, replace the solenoid.
- Start the engine and before the delay has timed out, measure the voltage of the black wire of the three way connector. The voltmeter should read charging system voltage. If it does not, replace the computer.
- Turning the air conditioning or the back light on should also produce charging system voltage after the time delay has timed out. If not, check the wiring back to the instrument panel for open circuits.
Dual Pick-Up Start/Run Relay Test
- Remove the two way connector from pins No. 4 and No. 5 of the dual pick-up start/run relay.
- Using an ohmmeter, touch pins No. 4 and No. 5. The meter should read 20-30 ohms. If not, replace the relay.