How to Set the Base Ignition Timing on a 4.3L V-6

The 4.3 liter V-6 engine used in GM trucks and vans, beginning in 1985, is based on the Chevy 350 small-block V-8. Beginning in 1988, this engine featured "Vortec" cylinder heads that created a swirling air/fuel mixture in the cylinder for improved combustion efficiency. Setting the base ignition timing in this engine is critical to the engine's performance, because on-board computer control of ignition timing during operation assumes base timing is accurate. The average home mechanic can complete this procedure in a few minutes.

STEP 1 - Start and warm the engine until the thermostat opens. The upper radiator hose will get hot when the thermostat opens and the coolant is circulating freely through the engine. This ensures normal operating temp has been reached and the on-board computer is operating in closed loop. Stop the engine.

STEP 2 - Set up the vehicle to adjust base timing. Clip the power cables of the timing light to the battery terminals and clip the inductive pick-up around the number one plug wire. The number one cylinder in the 4.3 V-6 is the front wire on the driver-side of the engine.

STEP 3 - Unplug timing connector to prevent the computer from changing the timing while you are adjusting it. The timing connector is a single wire connector containing a tan wire with a black stripe and is located taped to the outside of the main wiring harness on the firewall or behind the front carpet on the passenger-side floorboard of the vehicle.

STEP 4 - Loosen the hold down clamp bolt (found at the base of the distributor) 1/2 turn using a distributor wrench. Start the engine.

STEP 5 - Adjust the base timing by aiming the timing light at the timing marks on the front of the engine above the crankshaft pulley and balancer. Rotate the distributor by hand while observing the timing marks until the mark on the balancer lines up with the timing mark specified on the tune-up specifications tag located under the hood.

STEP 6 - Tighten the distributor hold down bolt and turn the engine off. Reconnect the timing connector. Remove the timing light and test-drive the vehicle to verify it runs properly.

THINGS YOU'LL NEED: Timing light

WARNINGS: Wear safety glasses and work gloves when working around a running engine to prevent serious injuries.

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