Toyota Pick-ups/Land Cruiser/4Runner 1970-1988

Ignition Timing

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See Figures 1, 2, 3, 4, 5, 6 and 7



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Fig. Fig. 1: Timing marks-8R-C and 18R-C engines



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Fig. Fig. 2: Timing marks-20R engine



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Fig. Fig. 3: Timing marks-22R engine (1981-84)



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Fig. Fig. 4: Timing marks-22R (1985-88), 22R-E and 22R-TE engines



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Fig. Fig. 5: Timing marks-3VZ-FE engine



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Fig. Fig. 6: Timing marks-F, 2F and 3F-E engines



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Fig. Fig. 7: Timing marks on crankshaft pulley

Ignition timing is the measurement in degrees of crankshaft rotation of the instant the spark plugs in the cylinders fire, in relation to the location of the piston, while the piston is on its compression stroke.

Ignition timing is adjusted by loosening the distributor locking device and turning the distributor in the engine.

Ideally, the air/fuel mixture in the cylinder will be ignited (by the spark plug) and just beginning its rapid expansion as the piston passes top dead center (TDC) of the compression stroke. If this happens, the piston will be beginning the power stroke just as the compressed (by the movement of the piston) air/fuel mixture starts to expand. The expansion of the air/fuel mixture will then force the piston down on the power stroke and turn the crankshaft.

It takes a fraction of a second for the spark from the plug to completely ignite the mixture in the cylinder. Because of this, the spark plug must fire before the piston reaches TDC, if the mixture is to be completely ignited as the piston passes TDC. This measurement is given in degrees (of crankshaft rotation) before the piston reaches top dead center (BTDC). If the ignition timing setting for your engine is seven (7°) BTDC, this means that the spark plug must fire at a time when the piston for that cylinder is 7° before top dead center of its compression stroke. However, this only holds true while your engine is at idle speed.

As you accelerate from idle, the speed of your engine (rpm) increases. The increase in rpm means that the pistons are now traveling up and down much faster. Because of this, the spark plugs will have to fire even sooner if the mixture is to be completely ignited as the piston passes TDC. To accomplish this, the distributor incorporates means to advance the timing of the spark as engine speed increases.

The distributor in your Toyota has two means of advancing the ignition timing. One is called centrifugal advance and is actuated by weights in the distributor. The other is called vacuum advance and is controlled by that larger circular housing on the side of the distributor.

In addition, some distributors have a vacuum retard mechanism which is contained in the same housing on the side of the distributor as the vacuum advance. The function of this mechanism is to retard the timing of the ignition spark under certain engine conditions. This causes more complete burning of the air/fuel mixture in the cylinder and consequently lowers exhaust emissions.

Because these mechanisms change ignition timing, it is necessary to disconnect and plug the one or two vacuum lines from the distributor when setting the basic ignition timing.

If ignition timing is set too far advanced (BTDC), the ignition and expansion of the air/fuel mixture in the cylinder will try to force the piston down the cylinder while it is still traveling upward. This causes engine "ping", a sound which resembles marbles being dropped into an empty tin can. If the ignition timing is too far retarded (after, or ATDC), the piston will have already started down on the power stroke when the air/fuel mixture ignites and expands. This will cause the piston to be forced down only a portion of its travel. This will result in poor engine performance and lack of power.

Ignition timing adjustment is checked with a timing light. This instrument is connected to the number one (No. 1) spark plug of the engine. The timing light flashes every time an electrical current is sent from the distributor, through the No. 1 spark plug wire, to the spark plug. The crankshaft pulley and the front cover of the engine are marked with a timing pointer and a timing scale. When the timing pointer is aligned with the 0 mark on the timing scale, the piston in the No. 1 cylinder is at TDC of its compression stroke. With the engine running, and the timing light aimed at the timing pointer and timing scale, the stroboscopic flashes from the timing light will allow you to check the ignition timing setting of the engine. The timing light flashes every time the spark plug in the No. 1 cylinder of the engine fires. Since the flash from the timing light makes the crankshaft pulley seem stationary for a moment you will be able to read the exact position of the piston in the No. 1 cylinder on the timing scale on the front of the engine.

There are three basic types of timing lights available. The first is a simple neon bulb with two wire connections (one for the spark plug and one for the plug wire, connecting the light in series). This type of light is quite dim, and must be held closely to the marks to be seen, but it is inexpensive. The second type of light operates from the battery. Two alligator clips connect to the battery terminals, while a third wire connects to the spark plug with an adapter. This type of light is more expensive, but the xenon bulb provides a nice bright flash which can even be seen in sunlight. The third type replaces the battery source with 110 volt house current. Some timing lights have other functions built into them, such as dwell meters, tachometers, or remote starting switches. These are convenient, in that they reduce the tangle of wires under the hood, but may duplicate the functions of tools you already have.

If your Toyota has electronic ignition, you should use a timing light with an inductive pickup. This pickup simply clamps onto the No. 1 plug wire, eliminating the adapter. It is not susceptible to crossfiring or false triggering, which may occur with a conventional light, due to the greater voltages produced by electronic ignition.

CHECKING & ADJUSTMENT



Carburetted Engines

See Figures 8, 9, 10, 11, 12, 13, 14 and 15

  1. Warm-up the engine. Connect a tachometer and check the engine idle speed to be sure that it is within the specification given in the "Tune-Up Specifications'' chart at the beginning of the section.
  2.  

Before hooking up a tachometer to a 1975-77 truck with a transistorized ignition system see the preceding "service precautions" in the "Breaker Points and Condenser" section.On models with electronic ignition, hook the positive (+) terminal of the dwell meter or tachometer to the negative (-) side of the coil, not to the distributor primary lead, on the 22R, hook the positive lead to the service connector on the igniter; damage to the ignition control unit will result. See illustrations.

  1. Clean off the timing marks. On the 2F, the timing marks are a ball on the flywheel and a pointer on the bellhousing. On all other engines, the marks are on the crankshaft pulley and timing cover. The timing notches in the crankshaft pulley are normally marked at the factory with red or white paint. You may want to retouch them if they are dark, using chalk or paint. Fluorescent (dayglow) paint is excellent for this purpose. You might have to bump the engine around with the starter to find the pulley marks.
  2.  
  3. Connect a timing light according to the manufacturer's instructions.
  4.  
  5. Disconnect the vacuum line(s) from the distributor vacuum unit. Plug it (them) with a pencil or golf tee(s).
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On 20R and 22R engines with HAC (High Altitude Compensation system) there are two vacuum hoses which connect to the distributor. Both must be disconnected and plugged. These systems require an extra step in the timing procedure, found at the end of this section. You can obtain more information about the HAC in Emission Controls .

  1. Be sure that the timing light wires are clear of the fan and start the engine.
  2.  


CAUTION
Keep fingers, clothes, tools, hair, and leads clear of the spinning engine fan. Be sure that you are running the engine in a well ventilated area!

  1. Allow the engine to run at the specified idle speed with the gearshift in Neutral with manual transmission and Drive (D) with automatic transmission.
  2.  


CAUTION
Be sure that the parking brake is set and that the front wheels are blocked to prevent the truck from rolling forward, especially when Drive is selected with an automatic!

  1. Point the timing light at the marks indicated in the chart and illustrations. With the engine at idle, timing should be at the specification given on the "Tune-Up Specifications'' chart at the beginning of the section.
  2.  
  3. If the timing is not at the specification, loosen the pinch bolt (holddown bolt) at the base of the distributor just enough so that the distributor can be turned. Turn the distributor to advance or retard the timing as required. Once the proper marks are seen to align with the timing light, timing is correct. If only minor corrections in the timing are necessary, adjustment can be made with the octane selector, rather than by moving the distributor. See the Octane Selector section following for further information.
  4.  
  5. Stop the engine and tighten the pinch bolt. Start the engine and recheck the timing. Stop the engine; disconnect the tachometer and timing light. Connect the vacuum line(s) to the distributor vacuum unit. Except on engines with HAC.
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  7. On engines with HAC (identified in the NOTE earlier) after setting the initial timing, reconnect the vacuum hose at the distributor. Recheck the timing. It should now be about 13° BTDC.
  8.  
  9. If the advance is still about 8°, pinch the hose between the HAC valve and the three way connector. It should now be about 13°. If not, the HAC valve should be checked for proper operation.
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Fig. Fig. 8: Tachometer hook-up-20R engine



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Fig. Fig. 9: Tachometer hook-up-22R engine



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Fig. Fig. 10: Tachometer hook-up at the check connector-22R-E, 22R-TE and 3VZ-E engines



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Fig. Fig. 11: Tachometer hook-up at the check connector-3F-E engine



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Fig. Fig. 12: Tachometer hook-up-22R-E and 22R-TE engines



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Fig. Fig. 13: Shorting the check connector-3F-E engine



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Fig. Fig. 14: Shorting the check connector-3VZ-E engine



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Fig. Fig. 15: Short circuit the terminals of the timing check connector T-E and check and adjust the timing, then unshort the connector-22R-E and 22R-TE engines

Fuel Injected Engines
  1. Connect a timing light to the engine following the manufacturer"s instructions.
  2.  

These engines require a special type of tachometer which hooks up to the service connector wire coming out of the distributor. You may also obtain an rpm reading by hooking the tachometer lead to the IG (-) terminal in the check connector found on the inner fender well. As many tachometers are not compatible with this hook-up, we recommend that you consult with the manufacturer before purchasing a certain type.

  1. Start the engine and run it at idle.
  2.  
  3. Remove the rubber cap from the check connector and short the connector at terminals (T-E), as shown.
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  5. Loosen the distributor pinch bolt just enough that the distributor can be turned. Aim the timing light at the marks on the crankshaft pulley and slowly turn the distributor until the timing mark is at the desired readings as listed in the "Tune-Up Specifications'' chart. Tighten the distributor pinch bolt.
  6.  
  7. Unshort the connector.
  8.  

 
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