How to Adjust the Timing on a 4.3Lby Dan Ferrell
Ever since General Motors added the 4.3L to its 90-degree V6 family of engines in 1985, several models, including full-size sedans, pickups and vans were fitted with the new machine configuration. The engine saw several modifications until its final production year in 1996. Many of the early 4.3L models allow for synchronization inspection and adjustment as part of their maintenance schedule. This means that you can adjust ignition timing in your garage and restore engine performance to your 4.3L engine model in a matter of minutes.
Locate the adjusting timing scale above the crankshaft pulley on the front and bottom of the engine. Wipe off dirt or grease from the timing scale marks with a shop rag and trace the marks with a white marker to make the numbers and dashes more visible during timing adjustment.
Locate the small groove mark on the crankshaft pulley. You will find it on the edge of the pulley as it rotates right in front of the timing scale. You might need to set your transmission to "Neutral" and rotate the crankshaft pulley clockwise with a breaker bar and socket to find this mark. Once you find it, trace it with the white marker to make it more visible during the timing adjustment.
Drive your vehicle for about 20 minutes on the highway, to make sure the engine reaches operating temperature, and go back to your driveway. Turn off the engine, set the parking brake and block the front and rear wheels with four wooden blocks.
Open the hood and connect a timing light to the engine. The two cables with the alligator clip terminals on the timing light hook up to the battery. The red clip connects to the positive (+) or red battery cable and the black clip connects to the ground (black) battery cable.
Connect the third cable on the timing light to the spark plug wire on the No. 1 cylinder. This third cable on the timing light has a clip that fully encloses the spark plug wire. The No. 1 cylinder is the closest to the front of the engine, the side where the drive or serpentine belt is located.
Unplug the thin rubber hose from the distributor advance. The advance is the metal, spinning top-shaped component on one side of the distributor. The distributor is where all the spark plug wires connect. Plug the thin hose opening with a screw or golf tee. If your 4.3L model does not come equipped with this distributor advance, look for the electronic spark timing (EST) connector, a small plastic cylinder with a single wire on each side. You may find it under the floor carpet on the passenger's side or near the brake booster inside the engine compartment on the driver's side or passenger side.
Find the emission label on the engine compartment, a small square label with tuneup information for your specific vehicle, and find the required engine speed or RPM for the engine during timing adjustment and the number indicating the correct timing for your specific vehicle model. Otherwise, look up the information in your vehicle service manual or call your local dealer.
Make sure the timing light wires are out of the way of the cooling fan, drive belts or other moving parts inside the engine compartment. Start the engine and have an assistant slightly step on the accelerator, if necessary, to speed up the engine to the required RPM.
Activate and aim the timing light at the timing marks on the crankshaft pulley. The strobe light will let you see the timing mark on the crankshaft pulley pointing to one of the numbers on the timing scale above the pulley. If the mark is pointing to the incorrect number on the scale, go to the next step. Otherwise, go to Step 11.
Loosen the bolt holding the distributor base to the engine using a wrench. Ask an assistant to grab the distributor body and slightly turn the distributor left or right, so the mark on the crankshaft pulley moves to the correct number on the timing scale. Tighten the distributor-mounting bolt and double check the pulley mark is still pointing to the correct number on the scale.
Shut off the engine and disconnect the timing light. Connect the distributor advance or EST electrical connector. Close the hood and remove the four wooden blocks from the wheels.
- Some 4.3L models, specially those produced since the early 1990s come equipped with an ignition system that directly communicates with the onboard computer for automatic timing adjustment. Check the emission label, your owner's manual or with your local dealer, if necessary, to make sure you can adjust the timing in your particular model.
Items you will need
- Shop rag
- White marker
- Breaker bar, if necessary
- Socket, if necessary
- 4 wooden blocks
- Timing light
- Screw or golf tee, if necessary
- "Chevrolet Full-size Automotive Repair Manual"; John Harold Haynes and Curt Choate; 1991
- "Modern Automotive Technology"; James E. Duffy; 2003
- Hemera Technologies/AbleStock.com/Getty Images