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1984 Dodge truck: coil..no main spark to the distributor

Customer Question
I have a 1984 Dodge...
I have a 1984 Dodge truck that will not start. Checked the coil and have got no main spark to the distributor. Replaced the coil and have the same problem. We have 12 volts coming in to positive side and 11 volts coming from the negative side of coil. When we try to start it, we get no power going to the dist. cap. Please help us with this problem and thank you very much for your help.
Submitted: 9 years ago.Category: Dodge
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Answered in 13 minutes by:
4/26/2008
Dodge Mechanic: ase_master327, Shop Owner replied 9 years ago
ase_master327
ase_master327, Shop Owner
Category: Dodge
Satisfied Customers: 5,288
Experience: +15 years experience with Dodge. Bumper to bumper diagnosis & repair.
Verified

OK, sounds like a pickup coil...

Either that or the module is bad, but the pickup is more common.

Here are testing instructions for the igntition system components on your engine:

 

  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.

Click image to see an enlarged view
Fig. 2: Remove 1-way connector from spark control computer

 

Click image to see an enlarged view
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. 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.

Click image to see an enlarged view
Fig. 4: Testing for voltage at coil positive

 

Click image to see an enlarged view
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.

Click image to see an enlarged view
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.

  2. 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.

Click image to see an enlarged view
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.

  2. Connect the negative (-) lead of the voltmeter to a good engine ground.

  3. 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.

Click image to see an enlarged view
Fig. 8: Power check; positioning paper insulator

 

Click image to see an enlarged view
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.

  2. 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.

  3. 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.

  4. 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.

  5. Install the distributor cap, reconnect all wiring and try to start the engine. If engine does not start replace the spark control computer.

  6. If, after installing the new computer, the engine still does not start, reinstall the original one and repeat the test.

Click image to see an enlarged view
Fig. 10: Checking continuity between terminal 2 and the ignition switch

 

Click image to see an enlarged view
Fig. 11: Checking continuity between terminal 7 and the carburetor switch

 

Click image to see an enlarged view
Fig. 12: Checking continuity in terminal 1

 

Click image to see an enlarged view
Fig. 13: Checking the resistance between terminals 5 and 9 and then, 3 and 9

 

Click image to see an enlarged view
Fig. 14: Checking the pickup resistance on a common distributor

 

Click image to see an enlarged view
Fig. 15: Checking each pickup coil terminal for ground on a common distributor

 

Click image to see an enlarged view
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.

Check your battery voltage, make sure it is at least 12.4 volts.

  1. 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.

Click image to see an enlarged view
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.

  2. 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.

  3. Remove the lead to coil (+) and connect a jumper wire between battery (+) and coil (+).

  4. 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.

  5. If spark is generated, replace the SMEC.

  6. If no spark is seen, use the special jumper and ground the coil negative (-) terminal directly.

  7. If spark is produced, repair the wiring harness for an open condition.

  8. If no spark is produced replace the ignition coil.

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Customer reply replied 9 years ago
There is no computor in this truck, and there is only one pick-up and run in this distributor. We have also replaced the ignition modulator and a two prong resistor
Dodge Mechanic: ase_master327, Shop Owner replied 9 years ago

Did you change the pickup in the distributor? It is what triggers the coil.

Put a plug wire on the coil, and a spark plug on the wire.

Disconnect the (-) wire from the coil, and turn the key on. Now get a jumper wire fro the ground on the battery, and touch it to the coil, then release it right quick...This simulates what the pickup coil does. When you remove the wire from the coil, if the plug sparks, then the pickup is bad inside the distributor.

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