It is wise to check the ignition timing at every tune-up, although timing varies little with electronic ignition systems. The manufacturer permits a tolerance of 2° on either side of the timing setting. Most engines run at their best and with maximum resistance to detonation if the timing is as close as possible to the setting.
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 0 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
2.0L & 2.6L Engines
See Figures 1 and 2
- Drive the vehicle until the engine is hot; the temperature gauge indicates normal operating temperature.
- Leave the engine idling, apply the handbrake and put the transmission in Neutral (manual) or P (automatic). Turn off all accessories.
- Install a tachometer, connecting the red lead to the negative terminal of the coil and the black lead to a clean ground (the battery negative terminal works well) or as otherwise detailed by the manufacturer of the tachometer. Verify that the engine idle speed is correct. If not adjust it. See the idle adjustment procedure later in this section.
- Stop the engine and connect a timing light according to the manufacturer's instructions.
- If the front pulley and timing marks are dirty, wipe them clean with a rag. If they are hard to see, you might want to put a small drop of white paint on both the timing scale and groove in the pulley. You may have to turn the engine over using a wrench on the bolt in the front of the crankshaft pulley to do this. Check the timing specifications on the Tune-up Charts or on the engine compartment sticker. Make sure all wires are clear of any rotating parts and the light is in a secure place. Make sure you haven't left any rags or tools near the engine.
If the tune-up specifications on the Vehicle Emission Control Information sticker in the engine compartment of your vehicle disagree with the Tune-Up Specifications chart in this section, the figures on the sticker must be used. The sticker often reflects changes made during the production run.
- If you are performing the timing procedure at high altitudes (more than 3,900 ft. above sea level), disconnect the pressure sensor electrical connector (if so equipped), located just across from the distributor wires at the top of the cap, before stopping the engine. The sensor is a box bolted to the fender with a vacuum hose connected to the bottom of the unit. Also disconnect the vacuum hose with the white stripes that is connected to the lowermost portion of the distributor vacuum advance, if so equipped. Plug the end of the hose.
- Start the engine and allow it to idle. Point the timing light at the mark on the front cover and read the timing by noting the position of the groove in the front pulley in relation to the timing mark or scale on the front cover. If the timing is incorrect, loosen the distributor mounting bolt or nut. Turn the distributor slightly clockwise to retard the timing or counterclockwise to advance it (advance means turning to a setting representing more degrees before top dead center). When the timing is correct, tighten the distributor mounting bolt and verify that the setting has not changed. If necessary, readjust the position of the distributor until the setting is correct after the bolt or nut is tight.
- If so equipped, reconnect the white striped vacuum hose or the pressure sensor connector. Recheck the timing. The timing should advance at high altitudes.
- Turn the engine off, disconnect the timing light and tachometer.
2.4L and 3.0L Engines See Figures 3, 4 and 5
For the timing adjustment procedure on these vehicles, you will need a jumper wire approximately two feet long with alligator clips on both ends. You will also need a paper clip. Make sure that you have these items on hand before attempting to check the timing.
- Drive the vehicle until the engine is hot; the temperature gauge indicates normal operating temperature. Apply the handbrake and put the transmission in Neutral (manual) or P (automatic). Turn off all accessories.
- Stop the engine and connect a timing light in accordance with the manufacturer's instructions.
- Trace the wire that runs from the primary side of the ignition coil to the noise filter. You will find a single terminal harness connector between these two points or locate the engine speed detection connectorrefer to the illustrations for location on your model. Insert a paper clip through the connector on either the female or the male side where the wire enters the connector, do not separate the connector. The paper clip must make full contact with the surface of the connector terminal and must be inserted at the proper angle or you will not be able to get it out.
- Once the paper clip is in place, connect a tachometer to it.
- Start the engine and check the idle speed. Adjust as necessary.
- Stop the engine and turn the ignition switch OFF .
- Connect a lead wire with alligator clips to the ignition adjustment terminal (refer to the illustration), and ground it.
- Start the engine and allow it to idle.
- Illuminate the timing marks on the crankshaft pulley with the timing light. Basic ignition timing should be between 3-7° BTDC.
- If the timing is not as specified, loosen the distributor mounting nut and turn the distributor to the right to retard the timing or to the left to advance it.
- Once the timing is set to specifications, tighten the mounting nut, being careful not to disturb the distributor.
- Stop the engine and disconnect the jumper wire from the ignition timing connector and ground.
- Start the engine and run it at idle speed.
If the tune-up specifications on the Vehicle Emission Control Information sticker in the engine compartment of your Dodge disagree with the specifications in this section, the figures on the sticker must be used. The sticker often reflects changes made during the production run.
- Check the timing again with the timing light. The timing should be 8° BTDC for the 2.4L and 15° BTDC for the 3.0L engines. This is called actual ignition timing. If the timing is not exactly 8° or 15°, do not be alarmed. This value may vary depending on what mode the computer is in at the time the base adjustment was made. If you do not see a change, check the base timing again. If the base timing is correct, the engine is in time and no further adjustment is necessary.
The ignition timing may vary from the specification even under normal operating conditions and is automatically further advanced at higher altitudes.