Jeep Wagoneer/Commando/Cherokee 1984-1998

Diagnosis and Testing

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SECONDARY SPARK TEST



See Figure 1

Since the only change between electronic and conventional ignition systems is in the distributor component area, it is imperative to check the secondary ignition circuit first. If the secondary circuit checks out properly, then the engine condition is probably not the fault of the ignition system. To check the secondary ignition system, perform a simple spark test.

  1. Remove one of the plug wires and insert some sort of extension in the plug socket. An old spark plug with the ground electrode removed makes a good extension.
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  3. Hold the wire and extension about 1 / 4 in. (6mm) away from the block and crank the engine. If a normal spark occurs, then the problem is most likely not in the ignition system. Check for fuel system problems, or fouled spark plugs.
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Fig. Fig. 1: Performing the secondary spark test

VACUUM ADVANCE



This is used on carbureted models only
  1. Bring the engine to operating temperature.
  2.  
  3. Disconnect the three-wire connector to the vacuum input switches, and disconnect and plug the vacuum hose from the distributor vacuum advance.
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  5. Connect a vacuum pump (available through local tool distributors) to the vacuum advance unit.
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  7. Connect a timing light to the No. 1 spark plug wire, and a tachometer to the negative terminal on the coil.
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  9. Start engine and increase engine speed.
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  11. While observing the timing degree scale with a timing light, apply vacuum to the distributor vacuum advance unit. If timing advances, the unit is functioning properly. If timing does not advance, replace the vacuum advance unit.
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  13. Stop engine, remove all test equipment, replace the three-wire connector and vacuum advance hose.
  14.  

CENTRIFUGAL ADVANCE



This is used on carbureted models only
  1. Bring the engine to operating temperature.
  2.  
  3. Disconnect the three-wire connector to the vacuum input switches, and disconnect and plug the vacuum hose from the distributor vacuum advance.
  4.  
  5. Connect a timing light to the No. 1 spark plug wire.
  6.  
  7. With the engine idling, slowly increase the speed and observe the timing mark. Timing should advance smoothly as engine speed increases. If timing advances unevenly, check and repair the centrifugal advance unit.
  8.  
  9. Stop engine, remove all test equipment, replace the three-wire connector and vacuum advance hose.
  10.  

 
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