Tiny spark at negative terminal as ground wire when attached

Terminal locations on the engine controller 14-way connector-1989 models
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Engine controller 60-way connector-relevant terminals for testing are shown numbered
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1. Attach one lead of a a voltmeter to the positive (12V) jumper wire. Attach the negative side of the voltmeter to a good ground. Measure the voltage at the battery and confirm that enough current is available to operate the starting and ignition systems.
   
2. Crank the engine for five seconds while monitoring the voltage at the coil positive terminal:
   
   1. If the voltage remains at zero, diagnosis of the fuel system should be performed. Also check the engine controller and auto shutdown relay.
      
   2. If voltage is at or near battery voltage and then drops to zero after one or two seconds of engine cranking, check the engine control module circuit.
      

The ignition must be turned OFF prior to unplugging the engine controller connector. If it is not, electrical surging could occur causing damage to the unit or other electrical components in the vehicle.

1. If the voltage remains at or near battery voltage during the entire five seconds, turn the ignition key OFF. Remove the 14-way connector on 1989 models, or the 60-way connector on 1990-96 models at the engine controller. Check the 14-way or 60-way connector for any spread terminals.
   

1. Remove the test lead from the coil positive terminal. Connect an 18 gauge jumper wire between the battery positive terminal and the coil positive terminal.
   
2. Make a special jumper cable (see illustration). Using the jumper MOMENTARILY ground terminal 12 on the 14-way connector (1989), or terminal 19 (see illustration) of the 1990-96 60-way connector. A spark should be generated at the coil wire when the ground is removed.
   
   1. If a spark is generated, replace the engine controller computer.
      
   2. If no spark is seen, use the special jumper to ground the coil negative terminal directly. If spark is produced, repair the wiring harness for an open circuit condition. If spark is not produced, replace the ignition coil
      
   this is for distributor ignition
   

This procedure requires an ohmmeter to test the coil packs for primary and secondary resistance (specifications are given for an ambient temperature of 70-80°F/21-27°C).

The two coil packs contain five independent coils, which fire paired cylinders (shown numbered)
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1. Disconnect the negative battery cable.
   
2. Determine the manufacturer of the coil. It should be labeled either a Diamond or Toyodenso.
   

Location of critical terminals for checking the coil primary resistance-V10 engine front coils
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Location of critical terminals for checking the coil primary resistance-V10 engine rear coils
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1. Check the secondary resistance of each individual paired coil by connecting an ohmmeter across the coil towers. This must be done between the correct cylinder pairs: 3/2, 7/4, 1/6, 9/8, or 5/10. Resistance for a Diamond coil should be 11,300-15,300 ohms. For a Toyodenso manufactured coil pack, resistance should be 11,300-13,300 ohms.
   

Use an ohmmeter to check secondary resistance as shown

1. Check the primary resistance of the front coil pack by attaching an ohmmeter between the B+ coil terminal and either the right (cylinders 3/2), center (cylinder 7/4), or left coil (cylinders 1/6) terminals. Resistance for a Diamond coil should be 0.97-1.18 ohms. Resistance for a Toyodenso coil should be 0.95-1.20 ohms.
   
2. To test the primary resistance of the rear coil pack, attach an ohmmeter between the B+ coil terminal (see illustration) and either the right (cylinders 9/8), or left (cylinders 5/10) coil terminals. Resistance for a Diamond coil should be 0.97-1.18 ohms. Resistance for a Toyodenso coil should be 0.95-1.20 ohms.
   

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