Mazda Trucks 1987-1993 Repair Guide

Diagnosis and Testing

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SERVICE PRECAUTIONS





Always turn the key OFF and isolate both ends of a circuit whenever testing for shorts or continuity.
 
Never measure voltage or resistance directly at the processor connector.
 
Always disconnect solenoids and switches from the harness before measuring for continuity, resistance or energizing by way of a 12-volt source.
 
When disconnecting connectors, inspect for damaged or pushed-out pins, corrosion, loose wires, etc. Service if required.
 

TESTING PROCEDURES



See Figure 1



Click image to see an enlarged view

Fig. Fig. 1: Basic electronic ignition troubleshooting

You will need an accurate ohmmeter, a jumper wire and a test light. Before proceeding with troubleshooting, make sure that all connections are tight and all wiring is intact.

  1. Check for spark at the coil high tension lead by removing the lead from the distributor cap and holding it about 1/4 inch (6mm) from the engine block or other good ground. Use a heavy rubber glove or non-conductive clamp, such as a fuse puller or clothes pin, to hold the wire.Crank the engine and check for spark. If a good spark is noted, check the cap and rotor; if the spark is weak or nonexistent, replace the high tension lead, clean and tighten the connections and retest. If a weak spark is still noted, proceed to Step 2.
  2.  
  3. Check the coil primary and secondary resistance. Refer to those procedures later in this section.
  4.  
  5. Next, remove the distributor cap and rotor.Crank the engine until a spoke on the rotor is aligned with the pickup coil contact. Use a flat feeler gauge to check the gap. Gap should be 0.20-0.60mm. The gap is not adjustable (procedure for 1987-88 B2600 air gap adjustment is covered later in this section). On these models (except 1987-88 B2600), gap is corrected by parts replacement.
  6.  
  7. On B2200 carbureted models, check the pickup coil resistance. If resistance is not correct, replace the pickup coil.
  8.  
  9. Finally, test the ignition module. The only way to test the module is to substitute a known good module in its place.
  10.  

IGNITION COIL SECONDARY VOLTAGE (SPARK) TEST



Crank Mode

See Figure 2



Click image to see an enlarged view

Fig. Fig. 2: Conducting a secondary spark test

  1. Connect a spark tester between the ignition coil wire and a good engine ground.
  2.  
  3. Crank the engine and check for spark at the tester.
  4.  
  5. Turn the ignition switch OFF.
  6.  
  7. If no spark occurs, check the following:
    1. Inspect the ignition coil for damage or carbon tracking.
    2.  
    3. Check that the distributor shaft is rotating when the engine is being cranked.
    4.  

  8.  
  9. If a spark did occur, check the distributor cap and rotor for damage or carbon tracking. Go to the Ignition Coil Secondary Voltage (Run Mode) Test.
  10.  

Run Mode

  1. Fully apply the parking brake. Place the gear shift lever in Neutral (manual transmission) or Park (automatic transmission).
  2.  
  3. Disconnect the S terminal wire at the starter relay. Attach a remote starter switch.
  4.  
  5. Turn the ignition switch to the RUN position.
  6.  
  7. Using the remote starter switch, crank the engine and check for spark.
  8.  
  9. Turn the ignition switch OFF .
  10.  
  11. If no spark occurred, the problem lies with the wiring harness. Inspect the wiring harness for short circuits, open circuits and other defects.
  12.  
  13. If a spark did occur, the problem is not in the ignition system.
  14.  

PICKUP COIL RESISTANCE



Unplug the primary ignition wire connector and connect an ohmmeter across the two prongs of the pickup coil connector. Resistance, at 68°F (20°C), should be 900-1,200 ohms.

EXTERNAL RESISTOR



See Figure 3



Click image to see an enlarged view

Fig. Fig. 3: Testing resistance of the external resistor

1987-1988 B2600 models are equipped with an external resister. Measure the resistance at the two end contacts on the resistor. Resistance should be 1.0-1.5 ohms.

SPARK ADVANCE CONTROL



Distributors not equipped with a crank angle sensor are equipped with two methods of spark advance. They are, an internal centrifugal advance consisting of governor weights and springs; and an external advance controlled by engine vacuum. Models equipped with fuel injection are equipped with an electronic advance device.

To test the internal advance:

  1. Connect a timing light to the engine.
  2.  
  3. Warm up the engine to normal operating temperature.
  4.  
  5. Check that the idle speed and ignition timing are correct.
  6.  
  7. Disconnect and plug the vacuum lines at the vacuum advance.
  8.  
  9. Gradually increase the engine speed while checking the timing mark with the timing light.
  10.  
  11. If the mark move to what seems like an excessive amount of advance, the cause could be a weak governor spring. If the mark moves slowly and seems like an insufficient amount of advance, the cause could be a governor weight or advance cam malfunction.
  12.  

To test the vacuum advance:

  1. Warm the engine to normal operating temperature.
  2.  
  3. Check that the idle speed and ignition timing are correct.
  4.  
  5. Disconnect the vacuum lines from the vacuum control and plug them.
  6.  
  7. Connect a vacuum hand pump to the vacuum control, slowly apply vacuum and check the advance with a timing light.
  8.  
  9. If the spark advance seems sluggish or not operating, replace the vacuum control.
  10.  

To test fuel injected models equipped with an electronic advance:

  1. Connect a timing light and verify that the timing advances with engine acceleration.
  2.  

 
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