You need to use a timing light to adjust timing.Base timing is 10 degrees BTDC)Before Top Dead Center.There is a mark on the balancer and you will need to disconnect the spout connector near the distributor to let the computer drop it into base timing mode.Timing is not adjustable on a 3.8 or 4.6 liter engine only the 5.0liter
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 the 5.0L engine does allow for both, should the distributor be removed and installed or otherwise disturbed.
See Figure 1
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 Top Dead Center (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.
Fig. 1: The ignition timing marks (arrow) are often stamped into the crankshaft damper assembly
If the ignition is set too 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 retarded, or After Top Dead Center (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 No. 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 pick-up should be used. This 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.
CHECKING & ADJUSTING
3.8L and 4.6L Engines
The 3.8L and 4.6L engines utilize the 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.
See Figures 2 through 5
SETTING INITIAL (BASE) TIMING
Specific instructions and specifications for setting initial timing can be found in the Vehicle Emission Control Information (VECI) label in the engine compartment. Because this label contains information regarding any specific calibration requirements for YOUR vehicle, those instructions and specifications should be followed if they differ from the following.
Fig. 2: VECI information is specific to YOUR car and should always be used if it differs from another source
Fig. 3: Using an alligator clip, a tachometer may be hooked up to the ignition coil connector
This procedure should not be used as a periodic maintenance adjustment. Timing should only be set after the distributor has been disturbed (removed and re-installed) in some way. If problems are encountered setting the initial timing with this procedure, and no mechanical causes are found, follow the spark timing advance check procedure later in this section.
Do not change the ignition timing by the use of a different octane rod without having the proper authority to do so. Federal emission requirements will be affected.
Start the engine and allow it to run until it reaches normal operating temperature.
Once normal operating temperature has been reached, shut the engine OFF.
Firmly apply the parking brake and block the drive wheels. Place the transmission in P (A/T) or NEUTRAL (M/T), as applicable.
Make sure the heater and A/C, along with all other accessories, are in the OFF position.
Connect an inductive timing light, such as the Rotunda 059-00006 or equivalent, to the No. 1 spark plug wire, according the tool manufacturer's instructions.
Connect a tachometer to the ignition coil connection using an alligator clip. This can be done by inserting the alligator clip into the back of the connector, onto the dark green/yellow dotted wire.
Fig. 4: If adjustment is necessary, loosen the distributor hold-down bolt
Fig. 5: Adjust the timing by rotating the distributor while observing the timing marks
DO NOT allow the alligator clip to accidentally ground to a metal surface while attached to the coil connector, as that could permanently damage the ignition coil.
Disconnect the single wire inline SPOUT connector which connects the control computer (usually terminal 36) to the ignition control module. This will prevent the electronic ignition from advancing the timing during the setting procedure.
Using a suitable socket or wrench, loosen the distributor hold-down bolt slightly at this time, BUT DO NOT ALLOW THE DISTRIBUTOR TO MOVE, or timing will have to be set regardless of the current conditions.
A remote starter must NOT be used to start the vehicle when setting the initial ignition timing. Disconnecting the start wire at the starter relay will cause the ignition control 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.
Start the engine (using the ignition key and NOT a remote starter to assure timing will be set correctly) and allow the engine to return to normal operating temperature.
With the engine running at the specified rpm, check the initial timing. If adjustments must be made, rotate the distributor while watching the timing marks. Once proper adjustment has been reached, make sure the distributor is not disturbed until the hold-down bolt can be secured.
Reconnect the single wire inline SPOUT connector and check the timing to verify that the distributor is now advancing beyond the initial setting.
Shut the engine OFF and tighten the distributor bolt while CAREFULLY holding the distributor from turning. If the distributor moves, you will have to start the engine and reset the timing.
Restart the engine and repeat the procedure to check the timing and verify that it did not change.
Shut the engine OFF, then disconnect the tachometer and timing light.
CHECKING SPARK TIMING ADVANCE
Spark timing advance is controlled by the Electronic Engine Control (EEC) system. This procedure checks the capability of the ignition module to receive the spark timing command from the EEC module. The use of a volt/ohmmeter is required.
Turn the ignition switch OFF.
Disconnect the pin-inline connector (SPOUT connector) near the TFI module.
Start the engine and measure the voltage, at idle, from the SPOUT connector to the distributor base. The reading should equal battery voltage.
If the result is okay, the problem lies within the EEC-IV system.
If the result is not satisfactory, separate the wiring harness connector from the ignition module. Check for damage, corrosion or dirt, and service as necessary.
Measure the resistance between terminal No. 5 and the pin-inline connector. This test is done at the ignition module connector only. The reading should be less than 5 ohms.
If the reading is okay, replace the TFI module.
If the result is not satisfactory, service the wiring between the pin-inline connector and the TFI connector.