GM Corvette 1984-1996 Repair Guide

Diagnosis and Testing

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SYSTEM TESTING



See Figures 1 through 10

Effective troubleshooting of the Opti-Spark ignition system requires a logical and systematic approach. The following charts are designed to help diagnose a no-spark condition or erratic spark plug firing. Refer to the system wiring chart before making any tester connections, and follow the steps in their prescribed order.


CAUTION
When handling secondary spark plug leads with the engine running or starting, insulated pliers must be used and care exercised to prevent a possible electrical shock.



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Fig. Fig. 1: Ignition system wiring-1992 5.7L (VIN P) engine



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Fig. Fig. 2: Ignition system check (1 of 2)-1992 5.7L (VIN P) engine



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Fig. Fig. 3: Ignition system check (2 of 2)-1992 5.7L (VIN P) engine



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Fig. Fig. 4: Ignition system wiring-1993-94 5.7L (VIN P) engine



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Fig. Fig. 5: Ignition system check (1 of 2)-1993-94 5.7L (VIN P) engine



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Fig. Fig. 6: Ignition system check (2 of 2)-1993-94 5.7L (VIN P) engine



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Fig. Fig. 7: Ignition system wiring-1995 5.7L (VIN P) engine



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Fig. Fig. 8: Ignition system wiring-1996 5.7L (VIN P and 5) engines



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Fig. Fig. 9: Ignition system check-1995-96 5.7L (VIN P and 5) engines



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Fig. Fig. 10: Ignition system diagnosis for misfire-1994-96 5.7L (VIN P and 5) engines

SPARK TEST



  1. With the engine off, disconnect a spark plug wire from a spark plug.
  2.  
  3. Connect the negative battery cable.
  4.  
  5. Connect a spark tester, such as tool ST-125, to the plug wire. Attach the clip to a good ground.
  6.  
  7. Have an assistant crank the engine. Check for spark at the tester. If there is no spark at one wire, check a second wire. It should be a bright blue color; if it is not, the coil may be faulty.
  8.  

IGNITION COIL



  1. Using an ohmmeter (on the high scale), connect the probes between the primary (low voltage) terminal and coil ground. The reading should be very high and infinity; if not, replace the coil.
  2.  
  3. Using an ohmmeter (on the low scale), connect the probes between both primary terminals. The reading should be very low or zero; if not, replace the coil.
  4.  
  5. Using an ohmmeter (on the high scale), connect the probes between a primary terminal and the secondary (high voltage) terminal. The reading should be high (not infinite); if not, replace the coil.
  6.  

DISTRIBUTOR VENTILATION SYSTEM CHECK



See Figures 11 and 12

The distributor ventilation system is used on 1995-96 vehicles. The distributor ventilation system vacuum harness is connected to the air intake duct, the distributor and the intake manifold. The vacuum harness provides ventilation for the distributor, preventing any moisture from accumulating and causing ignition system problems or failure.

The distributor vacuum harness attaches to the air intake duct and the intake manifold with vacuum fittings. It connects to the distributor at two places with separately sized connectors.



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Fig. Fig. 11: Distributor ventilation system components-1995 vehicles



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Fig. Fig. 12: Distributor ventilation system components-1996 vehicles

  1. Disconnect the distributor vacuum hose from the intake manifold. Connect a hand held vacuum pump to the distributor vacuum hose. Apply vacuum and observe the vacuum pump gauge. The vacuum should not build or should bleed off quickly.
  2.  
  3. If vacuum builds and does not bleed off quickly, check the system for blocked, restricted or collapsed hoses. Check the connections at the distributor cap for blockage. Check for a faulty check valve or check valve/filter.
  4.  
  5. If the vacuum bleeds off quickly, or does not build at all, leave the vacuum pump connected. Disconnect the distributor clean air supply hose from the air intake duct and plug it with a suitable stopper. Apply 10 in. Hg (34 kPa) of vacuum and observe the gauge. The vacuum should hold. If vacuum does not hold, check the system for vacuum leaks, damaged hoses or connections. Check the seal between the distributor cap and distributor and also, check the cap for cracks or damage. If vacuum does hold, proceed with the following steps.
  6.  
  7. Remove the stopper from the clean air supply hose. Disconnect the vacuum pump. Connect the vacuum pump to the clean air supply hose. Apply 10 in. Hg (34 kPa) of vacuum and observe the gauge. The vacuum should hold. If vacuum does NOT hold, the check valve is faulty and must be replaced. If the vacuum does hold, the system is OK, and you should check for a probable blocked or restricted vacuum source.
  8.  
  9. Once you determine the distributor ventilation system vacuum harness is operating properly, disconnect the vacuum gauge and reconnect the vacuum hose to the air intake duct.
  10.  

 
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