Chrysler Full-Size Trucks 1967-1988 Repair Guide

Ignition Coil

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TESTING



See Figure 1

Spark At Coil With Electronic Ignitions
  1. Set the parking brake and block the drive wheels.
  2.  
  3. Measure and note battery specific gravity and voltage. The gravity must be at least 1.220 (temperature corrected) in order to deliver the voltage necessary voltage to correctly operate the cranking and ignition systems.
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  5. Turn the ignition ON .
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  7. Remove the coil wire from distributor cap and, using an insulated tool, hold the end of the wire about 1 / 4 in. (6mm) away from a ground. DO NOT use bare hands to the wire.
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CAUTION
Do not use bare hands to hold any wires during a spark test. Always use an insulated tool to prevent the possibility of electrical shock

  1. Intermittently jump the coil negative wire to ground while looking for a spark at the coil wire. If spark is present, it should be bright blue in color and constant. Have a friend help you by cranking the engine while you slowly move the coil wire away from ground, looking for arching at the coil tower. If arching is present, replace the coil. If the spark is weak or not constant, or there is NO spark, continue testing.
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Fig. Fig. 1: Special jumper to ground coil negative

  1. If you have a good spark and no arching at the coil tower, your system is producing sufficiently high secondary voltage. However, make sure that this spark is getting to the plugs (check the distributor rotor, cap, spark plug cables, and plugs). If they are ok, then the ignition system is not your problem. Check for fuel system or engine mechanical trouble.
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On 10-Way Connector

See Figures 2 through 16

Before proceeding with this test make sure you have done a test for spark at the coil! Failure to do this could result in false test results.


WARNING
BE SURE TO SET THE PARKING BRAKE OR BLOCK THE DRIVE WHEELS BEFORE DOING THIS TEST!

  1. Turn the ignition switch in the OFF position and detach the 1-way connector from the bottom of spark control computer. Turn the ignition switch ON . Remove the coil wire from the distributor cap. Hold the end of the wire about 1 / 4 in. (6mm) away from a good engine ground. DO NOT use bare hands to hold the coil wire.
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Fig. Fig. 2: Remove 1-way connector from spark control computer



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Fig. Fig. 3: DO NOT test for spark during using your bare hands.

  1. Intermittently short coil negative (-) to ground using a jumper wire. If spark is obtained replace the spark control computer.
  2.  
  3. If no spark is obtained check for battery voltage at the coil positive (+) terminal with the ignition switch ON . It should be within one volt of a reading at the battery. If the voltage is correct, go to the next step. If the voltage is incorrect, check wiring between the battery and coil positive (+). Repair the wire and repeat this step.
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Fig. Fig. 4: Testing for voltage at coil positive



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Fig. Fig. 5: Checking coil positive-to-battery wire for continuity

  1. With the ignition switch ON , check for battery voltage at coil negative (-). It should be within one volt of the battery voltage. If it is correct go to the next step. If the voltage is incorrect, replace the coil.
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Fig. Fig. 6: Testing for voltage at coil negative

  1. If voltage is correct but no spark is obtained when shorting negative terminal, replace the coil.
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  3. If spark is obtained but the engine will still not start, turn ignition switch to the RUN position. With positive (+) lead of a voltmeter, measure the voltage from terminal 1 to ground of the disconnected lead from the computer. Voltage at each should be within 1 volt of previously noted battery voltage. If it is proceed ahead. If it is not, check the wire for an open circuit and repair (no power between coil negative (-) and the 1-way connector.) Repeat this step again.
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Fig. Fig. 7: Checking voltage from terminal 1 to ground

  1. Place a thin insulator (piece of paper) between curb idle adjusting screw and carb switch or make sure the curb idle adjusting screw is not touching the carb switch.
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  3. Connect the negative (-) lead of the voltmeter to a good engine ground.
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  5. Plug the 1-way connector into computer. Turn the ignition switch to the RUN position and measure voltage at the carb switch terminal. If the voltage is approximately 5 volts proceed ahead to Step 11. If the voltage is not at least 5 volts, turn the ignition switch to the OFF position and detach the 1-way connector from the bottom of the spark control computer. Turn ignition switch back to the RUN position and measure the voltage at terminal 2 of the connector. Voltage should be within 1 volt of previously noted battery voltage. If voltage is correct, repeat Step 1. If it is not, check the wiring between terminal 2 of connector and ignition switch for opens, shorts or poor connections.
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Fig. Fig. 8: Power check; positioning paper insulator



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Fig. Fig. 9: Testing terminal 2 for voltage

  1. Check with an ohmmeter for continuity between terminal 7 of the connector and the carb switch terminal. There should be continuity between these two points. If there is not, check the wire between them for opens, shorts or poor connections. If there is continuity between terminal 7 and the carb switch then, check for continuity between terminal 1 of the connector and engine ground. If there is continuity, replace the Spark Control Computer. If not, check the wire for opens or poor connections and repeat Step 13. Only proceed to Step 3 if the engine fails to start.
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  3. Turn the ignition switch to the OFF position and with an ohmmeter measure the resistance between terminals 5 and 9 for run pickup coil and between terminals 3 and 9 for start pickup coil of dual connector. Resistance should be between 8-900 ohms. If the resistance is 8-900 ohms proceed to Step 12. If it is not, disconnect the pickup coil leads from the distributor. Measure resistance at the lead going into the distributor. If the resistance is now between 8-900 ohms, this means there is an open, shorted or poor connection between distributor connector and terminals 5 and 9 or terminals 3 and 9 of the dual connector. Repair harness and repeat this step. If the resistance is still out of specifications, the pickup coil is bad. Replace the pickup coil and set the air gap to specifications then repeat this step.
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  5. Connect one lead of the ohmmeter to engine ground and with the other lead, check for continuity at each terminal of lead going to the distributor. There should not be any continuity. Reconnect the distributor lead and continue to Step 4. If there is continuity, replace the pickup coil.
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  7. Remove the distributor cap and check the air gap of the pickup coil. If it is not within specifications adjust. If it is, continue to next step.
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  9. Install the distributor cap, reconnect all wiring and try to start the engine. If engine does not start replace the spark control computer.
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  11. If, after installing the new computer, the engine still does not start, reinstall the original one and repeat the test.
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Fig. Fig. 10: Checking continuity between terminal 2 and the ignition switch



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Fig. Fig. 11: Checking continuity between terminal 7 and the carburetor switch



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Fig. Fig. 12: Checking continuity in terminal 1



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Fig. Fig. 13: Checking the resistance between terminals 5 and 9 and then, 3 and 9



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Fig. Fig. 14: Checking the pickup resistance on a common distributor



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Fig. Fig. 15: Checking each pickup coil terminal for ground on a common distributor



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Fig. Fig. 16: Checking the pickup coil air gap

On 3-Way Connector

See Figure 17

Before proceeding with this test make sure you have done a test for spark at the coil! Failure to do this could result in false test results.


WARNING
BE SURE TO SET THE PARKING BRAKE OR BLOCK THE DRIVE WHEELS BEFORE DOING THIS TEST!

  1. Check your battery voltage, make sure it is at least 12.4 volts.
  2.  
  3. Crank your engine for 5 seconds while checking the voltage at the coil (+). If voltage remains near zero during the entire period of cranking, you will need to do a check on the On-Board Diagnostic, for the Single Module Engine Controller (SMEC) and auto shutdown relay.
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Fig. Fig. 17: Single Module Engine Controller (SMEC) location

  1. If the voltage is at or near battery voltage and drops to zero after 1-2 seconds of cranking, check the On Board Diagnostic for the distributor reference pickup to the SMEC.
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  3. If voltage remains at or near battery voltage during the entire 56 seconds, remove the 3-way connector from SMEC (with the key OFF ). Check the 3-way connector for any spread terminals.
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  5. Remove the lead to coil (+) and connect a jumper wire between battery (+) and coil (+).
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  7. Using the special jumper used in testing spark at the coil, momentarily ground terminal #12 of the 3-way connector. A spark should be generated when the ground is removed.
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  9. If spark is generated, replace the SMEC.
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  11. If no spark is seen, use the special jumper and ground the coil negative (-) terminal directly.
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  13. If spark is produced, repair the wiring harness for an open condition.
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  15. If no spark is produced replace the ignition coil.
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REMOVAL & INSTALLATION



See Figures 18, 19, 20, and 21

  1. Disconnect the battery ground.
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  3. Disconnect the 3 wires from the coil. Mark them to identify for installation.
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Fig. Fig. 18: Disconnect the wires from the coil

  1. Disconnect the condenser suppressor connector from the coil, if equipped.
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  3. Unbolt and remove the coil.
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Fig. Fig. 19: Remove the bolts from the coil assembly



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