43-TBI Firing Order: 4.3L V6 Guide (1-6-5-4-3-2)
📡 Animated 43-TBI Firing Order Engine Diagram
Watch the real-time firing sequence illuminate each cylinder in the correct order: 1 → 6 → 5 → 4 → 3 → 2. This interactive animation helps you visualize how the spark travels and confirms the clockwise distributor terminal arrangement.
* Cylinders light up in firing sequence. Each full cycle = 2 engine revolutions (720°).
🧠 Why 1-6-5-4-3-2? Engineering & Advantage Analysis
The 4.3L V6 uses a 90° bank angle with split crankpin journals (each connecting rod pair shares a crank throw offset by 30°). The 1-6-5-4-3-2 firing order provides an even 120° crankshaft rotation between power strokes (720°/6 = 120°), which dramatically reduces torsional vibration and gives the engine a characteristic smooth idle compared to old odd-fire V6 designs. Types of firing orders in V6 engines: Odd-fire (early Buick) vs Even-fire (all GM 4.3L). The 43-TBI is even-fire with this exact numeric sequence.
✅ Advantages of Correct 1-6-5-4-3-2 Firing Order
- Improved volumetric efficiency – Intake manifold tuned for that sequence maximizes torque (typically 190–210 lb-ft).
- Lower exhaust gas temperatures – No cross-firing prevents lean condition spikes.
- Smoother crankshaft stress – Extends rear main seal life and flexplate durability.
- Better TBI fuel distribution – MAP and oxygen sensor see consistent pulses, enabling correct fuel trim.
⚠️ Disadvantages / Risks of Incorrect Firing Order
- Immediate damage: Backfire can blow off TBI air cleaner and rupture MAP sensor hose.
- Catalytic converter destruction within 20 miles of severe misfire (melted substrate).
- Hydrolock risk if raw fuel collects in cylinders due to non-firing cylinders.
- Ignition coil overheating due to improper load dwell.
🛠️ How To Set & Verify 43-TBI Firing Order (Professional Method)
Step 1: Safety first – disconnect battery, remove coil wire. Step 2: Remove #1 spark plug (front driver side). Step 3: Insert compression gauge or thumb over hole, bump starter until compression push; align timing mark to 0° TDC. Step 4: Inspect distributor rotor – it must point to the #1 cap terminal. Step 5: Install wires in clockwise sequence: attach #1 wire, then follow 6,5,4,3,2 around cap. Step 6: Double-check with firing order diagram. Step 7: Set base timing: with EST bypass disconnected, adjust to 0° (or 4° BTDC depending on emissions label). Reconnect bypass.
🗂️ Cylinder Numbering & Firing Order Reference Table
| Bank (Orientation) | Cylinder # | Firing Step Position | Relative crankshaft angle |
|---|---|---|---|
| Driver side (front) | 1 | 1st | 0° |
| Passenger side (rear) | 6 | 2nd | 120° |
| Driver side (rear) | 5 | 3rd | 240° |
| Passenger side (middle) | 4 | 4th | 360° |
| Driver side (middle) | 3 | 5th | 480° |
| Passenger side (front) | 2 | 6th | 600° |
📋 Common Diagnostic Trouble Codes (DTC) related to Firing Order
If firing order is messed up, PCM may store: P0300 (random misfire), P0301–P0306 (cylinder-specific misfire), P0420 (catalyst efficiency below threshold). Also, P0172 / P0175 (rich codes) because unburnt fuel passes into exhaust. Always verify firing order before replacing ignition components.
❗ Is It Safe To Change The 43-TBI Firing Order?
Absolutely not safe. The engine’s camshaft lobes, crankshaft journal offsets, ignition timing curve, and even the intake manifold runner design are tuned only for 1-6-5-4-3-2. Any deviation will cause severe backfire through the TBI, bent pushrods (due to pre-ignition), and immediate engine stalling. Never attempt to swap plug wire positions unless you are returning to OEM order.
🚗 Real-World Use Cases & Applications
This knowledge is vital when: replacing distributor (HEI module failure), engine rebuild, swapping long blocks, installing performance camshafts (verify overlap with same order), troubleshooting a no-start condition, or diagnosing misfire after a tune-up. Also, vintage TBI to carb conversion still requires the same firing order on the distributor cap.
