Jeep Wrangler Timing Instructionsby Dan Ferrell
You can adjust ignition timing on your Jeep Wrangler by rotating the distributor a few degrees. This procedure is possible on the 4.2L engine model only though. On 2.5L and 4.0L models, the Electronic Control Unit (ECU) controls ignition timing. Before starting, make sure you have the correct timing degree and RPMs at idle specified by the vehicle manufacturer. This information is located on the Vehicle Emission Control Information (VECI) label inside the engine compartment. If the label is missing, consult your car owner’s or vehicle service manual.
Preparing for Adjustment
Timing your Jeep is best after you have driven the vehicle for about 20 minutes to make sure the engine has reached operating temperature. Park the car in a safe place and set the transmission to Park (automatic) or Neutral (manual), apply the "Parking" brakes and turn off the engine.
Locate the timing scale on the case cover above the crankcase pulley at the engine front end and the notch on the crankcase pulley or vibration dumper, right next to the timing scale. If they are hard to see, clean the scale plate and pulley. Then highlight the marks with white chalk or correction fluid.
Hook up a timing light to the battery and clip the cable with the small, rectangular box at the end to the spark plug wire on the first cylinder (the cylinder closest to the front of the engine). Then disconnect the Computerized Emission Control (CSC) system vacuum switch wire. This wire is located on top of the valve cover. Also, unplug the vacuum hose at the distributor and plug the hose with a Phillips screwdriver of the appropriate size.
Make sure the timing light wires are out of the way of moving parts. At all times, during this procedure, be aware of the rotating cooling fan so that you do not touch it by accident with your hands or a piece of equipment.
Timing the Ignition System
Start the engine, increase the idle speed to 1600 rpm and adjust the idle to the number provided on the VECI label, following the procedure described in the same label. If you do not have this label, consult your car owner’s or vehicle service manual.
When ready, aim the timing light to the graduated scale on the front case cover and see what number on the scale the notch on the pulley points to. If you need to adjust it, loosen the nut on the distributor-holding clamp. Then, as you point the timing light on the scale, grab the distributor at the base and rotate it slowly, clockwise or counterclockwise, to align the notch on the crankcase pulley to the corresponding degree given on the VECI label. Then tighten the distributor clamp. Double check and make sure the notch is still pointing to the correct number.
After that, you can connect the hoses and correct the idle speed to the one specified on the VECI label. Then turn off the engine and remove the timing light.
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