Chrysler Front Wheel Drive Cars 4-CYL 1981-1995 Repair Information

Ignition Timing

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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. To do this, distributors have various means of advancing the spark timing as the engine speed increases. On some earlier model vehicles, this is accomplished by centrifugal weights within the distributor along with a vacuum diaphragm mounted on the side of the distributor. Later model vehicles are equipped with electronic ignition systems, in which the advance of the ignition timing is controlled by the Powertrain Control Module (PCM).

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 generally consist of a notch on the rim of the crankshaft pulley and a scale of degrees attached to the front of the engine (often on the engine front cover). The notch corresponds 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 mark on the pulley appear to be standing still. Proper timing is indicated when the notch is aligned with the correct number on the scale.

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 quite inexpensive. The second type of light is powered by the car's 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, but still attaches to the No. 1 spark plug wire in order to determine when the plug is fired. 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.

Never pierce a spark plug wire in order to attach a timing light or perform tests. The pierced insulation will eventually lead to an electrical arc and related ignition troubles.

An inductive pick-up timing light should be used with the Chrysler vehicles. The inductive pick-up 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



See Figure 1

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Fig. Fig. 1: Always refer to the VECI label located on the underside of the hood

For the correct timing specifications refer to the Vehicle Emission Control Information (VECI) label or the Tune-up Specifications chart in this section. If the VECI label and specifications chart disagree as to the correct ignition timing, always use the information on the VECI label. The VECI label reflects any running changes made by the manufacturer.

On all 2.2 and 2.5L except Premier engines, the timing marks are located on the flywheel with the pointer on an access hole in the transaxle, or on the edge of the access hole with a line on the flywheel. On 2.5L Premier and 2.6L engines, the timing marks are on a special bracket mounted on the front of the block and there is a notch in the front pulley.

1981-87 Models

See Figures 2 and 3

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Fig. Fig. 2: The timing marks for the 2.6L engine are located on a tab above the crankshaft pulley



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Fig. Fig. 3: The timing marks for the 2.2L EFI and 2.5L engines are located at the transmission/engine flange

  1. Warm the engine to normal operating temperature. Shut off the engine and connect the timing light to the No. 1 spark plug. Do not under any circumstances pierce a wire to hook up a light.
  2.  
  3. Clean off the timing marks and mark the pulley or damper notch and the timing scale with white chalk or paint. The timing notch on the damper or pulley can be elusive. Bump the engine around with the starter or turn the crankshaft with a wrench on the front pulley bolt to get it to an accessible position.
  4.  

The 2.2L and 2.5L engines have their timing marks on the flywheel and bell housing.

  1. Disconnect and plug the vacuum advance hose at the distributor or, at the spark advance computer vacuum transducer on (carbureted) models that have one in all years through 1987, to prevent any distributor advance. The computer is located in the air intake on the driver's side fender well, with the vacuum transducer's diaphragm clearly in view on top. The vacuum line is the rubber hose connected to the metal cone-shaped canister on the side of the distributor or the top/center of the transducer diaphragm. A short screw, pencil, or a golf tee can be used to plug the hose. On 1986 models equipped with a carburetor switch, connect a jumper wire between the carburetor switch and ground. On 1987 2.2 and 2.5L engines with Electronic Fuel Injection, disconnect the coolant temperature sensor electrical lead at the sensor, which is located on the thermostat housing.
  2.  

  1. Make sure the idle screw rests against its stop. If necessary, open and close the throttle to make sure the linkage is not binding. Start the engine and adjust the idle speed to that specified in the Tune-up Specifications chart. Since some cars require that the timing be set with the transmission in Neutral, you can disconnect the idle solenoid to lower the idle speed. If the vehicle is not equipped with an idle solenoid, adjust the idle speed screw to lower the idle speed. Adjusting the idle speed is vital, since it prevents any centrifugal advance from affecting the distributor timing.
  2.  
  3. Aim the timing light at the timing marks. Be careful not to touch the fan, which may appear to be standing still. Keep your clothes and hair, and the light's wire clear of the fan, belts, and pulleys. If the pulley or damper notch isn't aligned with the proper timing mark (see the Tune-up Specifications chart or the Vehicle Emission Control Information label on the underside of the vehicle's hood), the timing will have to be adjusted.
  4.  

Top Dead Center (TDC) corresponds to 0°; Before Top Dead Center (B or BTDC) may be shown as BEFORE; After Top Dead Center (A or ATDC) may be shown as AFTER.

  1. Loosen the distributor base clamp locknut. You can buy special wrenches which will make this task easy. Turn the distributor slowly to adjust the timing, holding it by the body and not the cap. Turn the distributor in the direction of rotor rotation (found in the Firing Order illustrations) to retard, and against the direction to advance.
  2.  
  3. Tighten the locknut. Check the timing, in case the distributor moved as you tightened it.
  4.  
  5. Reconnect the distributor vacuum hose. Correct the idle speed.
  6.  
  7. Shut off the engine and disconnect the light. Reconnect the coolant temperature sensor connector, if necessary.
  8.  

1988-95 Models
EXCEPT PREMIER

See Figures 3, 4, 5 and 6

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Fig. Fig. 4: To adjust the timing, loosen the hold-down screw and turn the distributor-except 2.5L Premier engine



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Fig. Fig. 5: The ECT sensor is mounted in the engine block next to the ignition coil-1988-95 models, except 1991-95 Sundance and Shadow



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Fig. Fig. 6: The ECT sensor for the 1991-95 Shadow and Sundance models is mounted in the water neck outlet housing

  1. Set the gearshift selector in Park or Neutral and apply the parking brake. All lights and accessories must be off.
  2.  
  3. Attach an inductive pick-up type of timing light to the No. 1 cylinder spark plug wire.
  4.  


WARNING
Do not puncture cables, boots or nipples with test probes. Always use the proper adapters. Also make sure that the timing light wires are not in the way of any moving engine components, such as the cooling fan.

  1. Start the engine and allow it to idle until normal operating temperature is reached.
  2.  

  1. Detach the Engine Coolant Temperature (ECT) sensor connector. The electric radiator fan will turn on and the malfunction indicator lamp (in the instrument panel) will turn ON after disconnecting the ECT sensor.
  2.  
  3. Aim the timing light at the timing marks. Be careful not to touch the fan, which may appear to be standing still. Keep your clothes and hair, and the light's wire clear of the fan, belts, and pulleys. If the pulley or damper notch isn't aligned with the proper timing mark (see the Tune-up Specifications chart or the Vehicle Emission Control Information label on the underside of the vehicle's hood), the timing will have to be adjusted.
  4.  

Top Dead Center (TDC) corresponds to 0°; Before Top Dead Center (B or BTDC) may be shown as BEFORE; After Top Dead Center (A or ATDC) may be shown as AFTER.

  1. Loosen the distributor base clamp locknut. You can buy special wrenches which will make this task easy. Turn the distributor slowly to adjust the timing, holding it by the body and not the cap. Turn the distributor in the direction of rotor rotation (found in the Firing Order illustrations) to retard, and against the direction to advance.
  2.  
  3. Tighten the locknut. Recheck the timing just in case the distributor moved as it was tightened.
  4.  
  5. Shut off the engine and disconnect the light. Reattach the ECT sensor connector. Some fault codes may be set, but they can be cleared immediately only with a special test instrument (DRB-II scan tool). However, as the ignition is turned ON and OFF 50-100 times (some later model years may take less re-starts to clear codes) in normal use, they will automatically be cleared by the system.
  6.  

PREMIER 2.5L ENGINE

If the initial timing is believed to be incorrect, refer to the distributor removal and installation procedure in Engine Electrical to reposition the distributor correctly, then perform teh following ignition timing procedure. The manufacturer does not supply a timing procedure; use this generic procedure.

  1. Set the gearshift selector in Park or Neutral and apply the parking brake. All lights and accessories must be off.
  2.  
  3. Attach an inductive pick-up type of timing light to the No. 1 cylinder spark plug wire.
  4.  


WARNING
Do not puncture cables, boots or nipples with test probes. Always use the proper adapters. Also make sure that the timing light wires are not in the way of any moving engine components, such as the cooling fan.

  1. Start the engine and allow it to idle until normal operating temperature is reached.
  2.  
  3. If equipped, disconnect and plug the vacumm hose attached to teh distributor.
  4.  
  5. Aim the timing light at the timing marks. Be careful not to touch the fan, which may appear to be standing still. Keep your clothes and hair, and the light's wire clear of the fan, belts, and pulleys. If the pulley or damper notch isn't aligned with the proper timing mark (refer to the Vehicle Emission Control Information label on the underside of the vehicle's hood or the Engine Tune-up Specifications chart in this section), the timing will have to be adjusted.
  6.  

Top Dead Center (TDC) corresponds to 0°; Before Top Dead Center (B or BTDC) may be shown as BEFORE; After Top Dead Center (A or ATDC) may be shown as AFTER.

  1. Loosen the distributor base clamp locknut. You can buy special wrenches which will make this task easy. Turn the distributor slowly to adjust the timing, holding it by the body and not the cap. Turn the distributor in the direction of rotor rotation (found in the Firing Order illustrations) to retard, and against the direction to advance.
  2.  
  3. Tighten the locknut. Recheck the timing just in case the distributor moved as it was tightened.
  4.  
  5. Shut off the engine and disconnect the light.
  6.  

 
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