Mazda Trucks 1994-1998 Repair Guide

Ignition Timing

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No periodic checking or adjustment of the ignition timing is necessary for any of the vehicles covered by this guide. However, the distributor ignition system used by 1994 B Series Pick-ups with 3.0L engines and all MPV models does allow for both, should the distributor be removed and installed or otherwise disturbed.

GENERAL INFORMATION



Ignition timing is the measurement, in degrees of crankshaft rotation, of the point at which the spark plugs fire in each of the cylinders. It is measured in degrees before or after Top Dead Center (TDC) of the compression stroke.

Because it takes a fraction of a second for the spark plug to ignite the mixture in the cylinder, the spark plug must fire a little before the piston reaches TDC. Otherwise, the mixture will not be completely ignited as the piston passes TDC and the full power of the explosion will not be used by the engine.

The timing measurement is given in degrees of crankshaft rotation before the piston reaches TDC (BTDC). If the setting for the ignition timing is 5° BTDC, the spark plug must fire 5° before each piston reaches TDC. This only holds true, however, when the engine is at idle speed.

As the engine speed increases, the pistons go faster. The spark plugs have to ignite the fuel even sooner if it is to be completely ignited when the piston reaches TDC. On all engines covered by this guide, spark timing changes are accomplished electronically by the engine and ignition control computers.

If the ignition is set too far advanced (BTDC), the ignition and expansion of the fuel in the cylinder will occur too soon and tend to force the piston down while it is still traveling up. This causes engine ping. If the ignition spark is set too far retarded, after TDC (ATDC), the piston will have already passed TDC and started on its way down when the fuel is ignited. This will cause the piston to be forced down for only a portion of its travel. This will result in poor engine performance and lack of power.

Timing marks consisting of O marks or scales can be found on the rim of the crankshaft pulley and the timing cover. The mark(s) on the pulley correspond(s) to the position of the piston in the number 1 cylinder. A stroboscopic (dynamic) timing light is used, which is hooked into the circuit of the No. 1 cylinder spark plug. Every time the spark plug fires, the timing light flashes. By aiming the timing light at the timing marks while the engine is running, the exact position of the piston within the cylinder can be easily read since the stroboscopic flash makes the pulley appear to be standing still. Proper timing is indicated when the mark and scale are in proper alignment.

Because these vehicles utilize high voltage, electronic ignition systems, only a timing light with an inductive pickup should be used. This pickup simply clamps onto the No. 1 spark plug wire, eliminating the adapter. It is not susceptible to cross-firing or false triggering, which may occur with a conventional light, due to the greater voltages produced by electronic ignition.

INSPECTION & ADJUSTMENT



1994 B Series Pick-up W/3.0L Engine

See Figure 1

Always refer to the Vehicle Emission Information Label in the engine compartment to verify the timing adjustment procedure.

  1. Place automatic transmission in PARK or manual transmission in NEUTRAL . The air conditioning and heater controls and all accessories should be in the OFF position.
  2.  
  3. Connect an inductive timing light and tachometer to the engine, according to the manufacturer's instructions.
  4.  



Click image to see an enlarged view

Fig. Fig. 1: Locate and disconnect the single in-line spout connector

  1. Disconnect the single wire in-line spout connector or remove the shorting bar from the double wire spout connector.
  2.  
  3. Start the engine and bring to normal operating temperature.
  4.  

To set timing correctly, a remote starter should not be used. Use the ignition key only to start the vehicle. Disconnecting the start wire at the starter relay will cause the TFI module to revert to start mode timing after the vehicle is started. Reconnecting the start wire after the vehicle is running will not correct the timing.

  1. Check the idle speed, and adjust if needed.
  2.  
  3. Check the initial timing by aiming the timing light at the timing marks and pointer. Refer to the underhood emission label for specifications.
  4.  
  5. If the marks do not align, shut off the engine and loosen the distributor hold-down bolt. Start the engine, aim the timing light and turn the distributor until the timing marks align. Shut off the engine and tighten the distributor hold-down bolt.
  6.  
  7. Reconnect the single wire in-line spout connector or reinstall the shorting bar on the double wire spout connector. Check the timing advance to verify the distributor is advancing beyond the initial setting.
  8.  
  9. Remove the timing light and tachometer.
  10.  

MPV Model With 2.6L Engine

See Figures 2 and 3



Click image to see an enlarged view

Fig. Fig. 2: Connect a jumper wire to the Data Link Connector-1994-95 2.6L and 3.0L engines



Click image to see an enlarged view

Fig. Fig. 3: Location of timing marks above the crankshaft pulley

  1. Apply the parking brake and place the gearshift lever in P .
  2.  
  3. Start the engine and bring to normal operating temperature. Make sure all electrical loads and the A/C switch are OFF .
  4.  
  5. Connect a timing light and connect a tachometer to the IG terminal of the diagnostic connector.
  6.  
  7. Connect a jumper wire between the TEN and GND terminals of the diagnostic connector.
  8.  
  9. Check the idle speed and adjust, if necessary. The idle speed should be 780-820 rpm.
  10.  
  11. Aim the timing light at the timing scale on the timing belt cover and the timing mark on the crankshaft pulley. The timing should be 4-6 degrees BTDC.
  12.  
  13. If the timing is not as specified, loosen the distributor mounting bolt and turn the distributor to adjust. After adjustment, tighten the bolt to 19 ft. lbs. (25 Nm) and recheck the timing.
  14.  
  15. Remove the jumper wire and all test equipment.
  16.  

MPV Model With 3.0L Engine
1994-95

See Figures 4 and 5

  1. Apply the parking brake and place the gearshift lever in P .
  2.  
  3. Start the engine and bring to normal operating temperature. Make sure all electrical loads and the A/C switch are OFF .
  4.  
  5. Connect a timing light and connect a tachometer to the IG terminal of the diagnostic connector.
  6.  
  7. Connect a jumper wire between the TEN and GND terminals of the diagnostic connector.
  8.  
  9. Check the idle speed and adjust, if necessary. The idle speed should be 780-820 rpm.
  10.  
  11. Aim the timing light at the timing scale on the timing belt cover and the timing mark on the crankshaft pulley. The timing should be 4-6 degrees BTDC.
  12.  
  13. If the timing is not as specified, loosen the distributor mounting bolt and turn the distributor to adjust. After adjustment, tighten the bolt to 19 ft. lbs. (25 Nm) and recheck the timing.
  14.  
  15. Remove the jumper wire and all test equipment.
  16.  

1996-98

See Figures 4



Click image to see an enlarged view

Fig. Fig. 4: SST 49 B019 9A0 system selector-1996-98 3.0L engine

  1. Apply the parking brake and place the gearshift lever in P .
  2.  
  3. Start the engine and bring to normal operating temperature. Make sure all electrical loads and the A/C switch are OFF .
  4.  
  5. Connect a timing light to the high-tension lead No. 1.
  6.  
  7. Connect the SST 49 B019 9A0 (system selector) to the data link connector.
  8.  
  9. Set the switch A to position No. 1 and set the test switch to SELF TEST. Verify that the idle speed is within specifications. If not, adjust it. Specification is 500-900 rpm.
  10.  
  11. Verify that the timing mark (yellow) is within the specification. Specification is BTDC 10-12°.
  12.  
  13. If not as specified, loosen the distributor lock bolts and turn the distributor to make the adjustment.
  14.  
  15. Tighten the distributor lock bolts to 14-18 ft. lbs. (19-25 Nm).
  16.  
  17. Disconnect the SST (system selector) and verify that the timing mark (yellow) is within specification. Specification is ATDC 2-BTDC 34°.
  18.  
  19. Stop the engine and disconnect the timing light.
  20.  

Except 1994 B Series Pick-ups W/3.0L Engine and All MPV Models

These engines utilize a Distributorless Ignition System (DIS). On this system, ignition coil packs fire the spark plugs directly through the spark plug wires. All spark timing and advance is determined by the ignition control module and engine control computer. No ignition timing adjustments are necessary or possible.

 
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