The firing order for the 4.3L V6 used in Chevrolet S-10 pickups is 1-6-5-4-3-2.
The 4.3 S-10 uses a 90-degree GM V6 layout where the cylinders fire in a fixed sequence. This sequence matters when installing spark plug wires, routing a distributor cap, or checking engine timing. In this article, we explain the order, how cylinders are numbered, and how to verify or adjust timing on a 4.3 S-10 engine.
Firing order and cylinder numbering
To help you visualize the sequence, here are the core facts you’ll need when wiring or diagnosing the engine.
- Firing order: 1-6-5-4-3-2 for the 4.3L V6 commonly used in S-10s.
- This firing sequence applies to the GM 4.3L V6 family, including variants used in S-10, Blazer, and other GM trucks during the era.
- When wiring or replacing the distributor or spark plugs, follow the 1-6-5-4-3-2 order around the cap and wires.
Correctly following this order helps prevent cross-firing and misfires, which can cause rough idle, reduced power, and poor fuel economy. Always verify against your vehicle’s service manual for any year-to-year variations.
Verifying or adjusting timing on a 4.3 S-10
When you need to verify or adjust ignition timing, use the following steps as a guide. Note that exact degrees and procedures can vary by year and model, so consult the factory manual for your truck.
- Disconnect the negative battery cable to prevent accidental cranking.
- Locate the distributor (if your engine uses a traditional distributor) and the timing marks on the crank pulley and timing cover.
- With the engine at TDC on the first cylinder’s compression stroke, confirm that the rotor points toward the terminal corresponding to cylinder 1 on the distributor cap.
- Rotate the distributor slightly to bring the rotor toward the correct position for the 1-6-5-4-3-2 sequence, then tighten the distributor hold-down.
- Reconnect the battery, start the engine, and verify idle timing using the timing marks or a scan tool. Readjust if necessary per the manual.
Note: Some 4.3L engines use distributorless ignition or coil packs; in those cases, timing is controlled by the engines’ sensors and PCM, and you won’t rotate a distributor. Always follow your specific model’s service manual.
Cylinder numbering and bank layout
In most GM 4.3L V6 configurations, odd-numbered cylinders are on one bank and even-numbered cylinders on the opposite bank. The front-to-rear order and the exact bank designation can vary by model year and vehicle orientation. Check your engine’s deceleration plate or service manual for the precise cylinder map and the location of cylinder 1.
Additional notes and safety considerations
Working on ignition systems can be dangerous. Ensure the engine is cool, wear eye protection, and disconnect the battery before touching wiring. If you’re unsure about the exact firing order for your year, or if you have a distributorless ignition system, seek a qualified mechanic or consult the official GM service documentation.
Summary
The essential firing order for the Chevrolet S-10’s 4.3L V6 is 1-6-5-4-3-2. This sequence guides spark plug wiring and timing checks. Always verify with your year’s service manual, because some variants or ignition systems (distributor vs distributorless) may alter how timing is set. With the right order, you’ll ensure smooth operation and optimal power from the engine.