Jeep Wrangler/YJ 1987-1995 Repair Guide

Troubleshooting

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See Figures 1

INITIALIZATION



When the ignition system is turned OFF , the MCU is also turned off. It has no long term memory circuit for prior operation. As a result, it has an initialization function that is activated when the ignition switch is turned ON .

The MCU initialization function moves the metering pins to the predetermined starting position by first driving them all the way to the rich end stop and then driving them in the lean direction a predetermined number of steps. No matter where they were before initialization, they will be at the correct position at the end of every initialization period. Because each open loop operation metering pin position is dependent on the initialization function, this function is the first test in the diagnostic procedure.

The CEC System should be considered as a possible source of trouble for engine performance, fuel economy and exhaust emission complaints only after normal tests that would apply to an automobile without the system have been performed.



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Fig. Fig. 1: Vacuum switch solenoid-4.2L engine

PRELIMINARY TESTS



Before performing the Diagnostic Tests, other engine associated systems that can affect air/fuel mixture, combustion efficiency or exhaust gas composition should be tested for faults. These systems include:

  1. Basic carburetor adjustments.
  2.  
  3. Mechanical engine operation (spark plugs, valves, rings, etc.).
  4.  
  5. Ignition system components and operation.
  6.  
  7. Gaskets (intake manifold, carburetor or base plate); loose vacuum hoses or fittings, or loose electrical connections.
  8.  

DIAGNOSTIC TESTS



See Figures 2 through 28

One of the most common problems with electronic engine control systems results not from a faulty component, but from a bad circuit which is caused by loose, dirty or corroded connections. Always begin diagnosis by checking all wiring and hoses from proper connections, routing and lack of physical damage.

If a visual inspection does not turn up the problem and the preliminary tests do not reveal a mechanical problem or some other cause of improper operation, proceed with the diagnostic flow charts in order to troubleshoot the condition. As necessary, refer to other information in this guide for additional information on engine, fuel and ignition system components.



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Fig. Fig. 2: Stepper motor connector-4.2L engine



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Fig. Fig. 3: Coolant temperature switch-4.2L engine



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Fig. Fig. 4: 4 and 10-inch vacuum switches-4.2L engine



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Fig. Fig. 5: CEC system wiring diagram-4.2L engine



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Fig. Fig. 6: CEC system diagnostic test and system connectors-4.2L engine



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Fig. Fig. 7: CEC system diagnostic test-4.2L engine



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Fig. Fig. 8: CEC system diagnostic test-4.2L engine



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Fig. Fig. 9: CEC system diagnostic test-4.2L engine



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Fig. Fig. 10: CEC system diagnostic test-4.2L engine



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Fig. Fig. 11: CEC system diagnostic test-4.2L engine



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Fig. Fig. 12: CEC system diagnostic test-4.2L engine



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Fig. Fig. 13: CEC system diagnostic test-4.2L engine



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Fig. Fig. 14: CEC system diagnostic test-4.2L engine



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Fig. Fig. 15: CEC system diagnostic test-4.2L engine



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Fig. Fig. 16: CEC system diagnostic test-4.2L engine



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Fig. Fig. 17: CEC system diagnostic test-4.2L engine



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Fig. Fig. 18: CEC system diagnostic test-4.2L engine



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Fig. Fig. 19: CEC system diagnostic test-4.2L engine



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Fig. Fig. 20: CEC system diagnostic test-4.2L engine



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Fig. Fig. 21: CEC system diagnostic test-4.2L engine



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Fig. Fig. 22: CEC system diagnostic test-4.2L engine



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Fig. Fig. 23: CEC system diagnostic test-4.2L engine



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Fig. Fig. 24: CEC system diagnostic test-4.2L engine



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Fig. Fig. 25: CEC system diagnostic test-4.2L engine



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Fig. Fig. 26: CEC system diagnostic test-4.2L engine



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Fig. Fig. 27: CEC system diagnostic test-4.2L engine



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Fig. Fig. 28: CEC system diagnostic test-4.2L engine

 
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