No periodic adjustment of the ignition timing is necessary for any of the vehicles covered by this guide. However, the ignition system used on the 1.5L (VIN J), 1.6L (VIN R), 1.8L (VIN M) AND 3.0L (VIN T) engines does allow for adjustment, should the distributor be removed or otherwise disturbed.
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.
Ideally, the air/fuel mixture in the cylinder will be ignited by the spark plug just as the piston passes TDC of the compression stroke. If this happens, the piston will be at the beginning the power stroke just as the compressed and ignited air/fuel mixture forces the piston down and turns the crankshaft. 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, each spark plug must fire 5 degrees 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 in this guide, spark timing changes are accomplished electronically by the Electronic Control Module (ECM) based on input from engine sensors.
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 started on its way down when the fuel is ignited. The piston will be forced down for only a portion of its travel, resulting in poor engine performance and lack of power.
Timing marks or scales can be found on the rim of the crankshaft pulley and the timing cover. The marks on the pulley correspond to the position of the piston in the No. 1 cylinder. A stoboscopic (dynamic) timing light is hooked onto the No. 1 cylinder spark plug wire. Every time the spark plug fires, the timing light flashes. By aiming the light at the timing marks while the engine is running, the exact position of the piston within the cylinder can be easily read (the flash of light makes the mark on the pulley appear to be standing still). Proper timing is indicated when the mark and scale are in specified alignment.
INSPECTION & ADJUSTMENT
See Figures 1, 2, 3, 4, 5, 6 and 7
1.5L (VIN J), 1.6L (VIN R), 1.8L (VIN M) and 3.0L (VIN T) Engines
Do not use a scan tool to check ignition timing. A scan tool connected to the data link connector reads the ordinary ignition timing, not the basic the ignition timing (with timing connector grounded) that is necessary to set timing properly.
- Place the vehicle in P or N with the emergency brake applied and the drive wheels blocked.
- Start the engine and let it reach normal operating temperature. Make sure all accessories are off.
- Connect a suitable tachometer and timing light to the engine, as per the manufacturers' instructions.
- On 1.6L (VIN R) and 1.8L (VIN M) engines, increase engine speed to 2,000-3,000 rpm for 5 seconds, then allow engine to idle for 2 minutes
- Check that the idle speed is within the specified rpm range and adjust as necessary.
- Stop the engine and connect a jumper wire from the ignition timing adjustment connector (located at the rear of the engine compartment) to ground.
- Start engine and allow it to idle.
- Following the manufacturer's instructions, aim the timing light and check the basic ignition timing. As the light flashes, note the position of the mark on the crankshaft pulley against the scale on the timing cover. Basic timing (with the connector grounded) should be 3-7 degrees BTDC.
- If timing is not within specification, loosen the distributor hold-down nut and turn the distributor as needed to obtain a proper basic timing.
- Tighten the distributor hold-down nut to 7-9 ft. lbs. (10-13 Nm).
- Recheck the basic timing and readjust as necessary.
- Stop the engine and remove the jumper wire. Be sure to remove the tachometer and timing light.