Jeep Wrangler/YJ 1987-1995 Repair Guide

Powertrain Control Module (PCM) System

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All 1993-95 2.5L and 4.0L Engines are equipped with multi-port fuel injection. The ignition system on these engines is operated by the Powertrain Control Module (PCM) and consists of:



Spark plugs
 
Secondary ignition cables
 
Ignition coil
 
Distributor (contains rotor and camshaft position sensor)
 
Powertrain Control Module
 
Crankshaft position sensor
 

DIAGNOSIS



Failure To Start Test

See Figures 1, 2, 3 and 4



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Fig. Fig. 1: Special jumper wire construction for grounding the coil



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Fig. Fig. 2: Common coil harness connector



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Fig. Fig. 3: Coil terminals



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Fig. Fig. 4: PCM 60-way electrical connector

Apply parking brake and block wheels before performing any engine running tests, including idle or timing checks and adjustments.

  1. Check battery voltage and determine that a minimum of 12.4 volts is available for operation of cranking and ignition systems.
  2.  
  3. Crank engine for 5 seconds while monitoring voltage at coil positive terminal. If voltage remains near 0 during entire period of cranking, please refer to Fuel System in this guide for on-board diagnostic checks of PCM and auto shutdown relay.
  4.  
  5. If measured voltage is near battery voltage but drops to 0 after 1-2 seconds of cranking, please refer to Fuel System in this guide for on-board diagnostic checks of distributor reference pick-up circuit to PCM.
  6.  
  7. If measured voltage remains near battery voltage for entire 5 second cranking period, turn key OFF and remove SBEC 60-way connector. Check 60-way connector for any spread terminals.
  8.  
  9. Remove the wire-to-coil positive terminal and connect regular jumper wire between coil positive terminal and battery positive terminal.
  10.  
  11. Using a special jumper cable, momentarily ground terminal No. 19 of the PCM 60-way connector. A spark should be generated when ground is removed:
    1. If spark is generated, replace the PCM.
    2.  
    3. If no spark is seen, use a special jumper to ground the coil negative terminal directly. If spark is produced by directly grounding the negative coil terminal, but was not produced with pin No. 19, trace and repair open condition within wiring harness. If no spark is produced when directly grounding the coil, the faulty ignition coil should be replaced.
    4.  

  12.  

Secondary Circuit Testing

  1. Remove the center wire from the distributor cap.
  2.  
  3. Using insulated pliers, hold the terminal end about 1 / 2 in. (13mm) from a good engine ground and crank the engine.
  4.  
  5. Check for steady arcing. If steady arcing does not occur, inspect the secondary coil cable. Also, inspect the distributor cap and rotor for cracks or burn marks, then repair as necessary.
  6.  
  7. Remove the cable from one spark plug.
  8.  
  9. Using insulated pliers, hold the terminal end about 1 / 2 in. (13mm) from the block or head and crank the engine.
  10.  
  11. If a spark occurs, check ECU sensors using tester DRB II, or equivalent. If the sensors check out okay, the problem is probably in the fuel system.
  12.  
  13. If no spark occurs, The rotor, distributor cap or spark plug wires are defective.
  14.  

 
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