Datsun 240Z Firing Order: 1-5-3-6-2-4 Sequence
🎯 Detailed Firing Order for Datsun 240Z (L24 Engine)
Exact sequence: Cylinder 1 → Cylinder 5 → Cylinder 3 → Cylinder 6 → Cylinder 2 → Cylinder 4 → then repeats. Cylinder numbering: #1 at front (timing chain side), #2, #3, #4, #5, #6 towards firewall. Distributor rotation is clockwise when viewed from the front. The ignition rotor passes cap terminals in that order.
🔢 Cylinder Layout
Front of car
1 – 2 – 3 – 4 – 5 – 6
Firewall
Firing: 1,5,3,6,2,4
🗺️ Distributor Cap Order (clockwise)
Terminal #1 (usually marked) → #5 → #3 → #6 → #2 → #4. Use quality copper or resistor core wires.
⚙️ Why This Firing Order? – Engineering Deep Dive
The 1-5-3-6-2-4 firing order is not random. It provides:
- Primary balance: The inline-6 is naturally balanced in primary and secondary forces; this firing order maintains that by firing cylinders 120° apart.
- Crankshaft torsional harmony: Loads are applied to crankpins in a pattern that reduces stress and prevents harmonic breakage at high RPM.
- Intake manifold design: The L24’s intake runners are tuned to the sequence, avoiding reversion pulses between adjacent cylinders.
- Even cooling & thermal load: No two adjacent cylinders fire consecutively, so heat distributes evenly across the cylinder head.
🛠️ How to Check & Set the Firing Order on a Datsun 240Z – Step by Step
Follow this procedure to verify or correct the firing order on your L24 engine.
- Safety first: Disconnect battery negative terminal. Work on cold engine.
- Locate cylinder #1: Frontmost cylinder on passenger side (LHD) – directly under #1 spark plug.
- Remove distributor cap: Note rotor rotation direction (clockwise). Rotor should point to #1 terminal when engine is at TDC compression.
- Set engine to TDC #1: Turn crankshaft pulley clockwise until timing mark aligns with 0° (TDC) and rotor points to #1 tower.
- Route spark plug wires: Connect #1 wire to its terminal, then going clockwise attach wires to cylinders 5, 3, 6, 2, 4 in that order.
- Double-check wire lengths: Cylinders 1,2,3 (front group) and 4,5,6 (rear group) – ensure no cross-talking.
- Start engine & time it: Use timing light to set ignition timing at 10° BTDC (vacuum advance disconnected).
📊 Comparison: Firing Order Types & L24 Specifics
| Firing Order Type | Example Engines | Characteristics |
|---|---|---|
| 1-5-3-6-2-4 | Datsun L24/L28, Toyota M/JZ, BMW M30 | Smooth idle, excellent balance, used in 90% of inline-6s |
| 1-4-2-5-3-6 | Jaguar XK6, some older Chevy 250 | Different firing interval, slightly rougher but reduces certain harmonic orders |
| 1-4-5-2-3-6 | Rare modified racing engines | Requires custom cam, not for street L24 |
🔍 Is It Safe to Alter the Firing Order on a Datsun 240Z?
Absolutely NOT safe. The L24 engine’s camshaft lobe phasing, crankshaft journal offsets, and intake/exhaust valve timing are physically engineered for the 1-5-3-6-2-4 sequence. Changing the firing order would require a custom camshaft with different lobe positions and a modified crankshaft, which is impractical and extremely dangerous for a street engine. Attempting to “swap wires” to a different order will result in immediate misfire, backfire through the intake, bent valves due to incorrect valve timing, and potential engine fire. Always stick to factory order.
✅ Advantages of Correct Firing Order (Datsun 240Z)
- Ultra-smooth idle – classic Z-car refinement.
- Maximum power output – 151 hp achieved at 5600 RPM.
- Long engine life – even bearing wear, no destructive harmonics.
- Responsive throttle – correct ignition phasing.
- Better fuel economy – complete combustion reduces waste.
❌ Disadvantages of Incorrect Firing Order (Symptoms)
- Heavy engine vibration – can break motor mounts.
- Backfiring through carbs or exhaust – dangerous fire risk.
- Loss of 50%+ power – unburned fuel in exhaust.
- Hard starting / no start – wrong sequence prevents combustion.
- Catalytic converter damage (if fitted) due to raw fuel.
- Valve & piston damage from pre-ignition or backfire pressure.
🧰 Practical Use & Performance Tuning Relevance
When upgrading to electronic ignition (Pertronix, 280ZX distributor), or replacing spark plug wires, always verify the firing order. For high-performance L24 builds (bigger cam, triple Weber carbs), the firing order remains unchanged; only ignition timing curves and advance are optimized. Racers often “phase” the distributor rotor for precise alignment, but the sequence 1-5-3-6-2-4 remains inviolable. Use a dial-back timing light to confirm each cylinder’s firing event matches the order.
📋 Complete Firing Order Verification Checklist
- ☑️ Cylinder numbering confirmed (front = #1).
- ☑️ Distributor cap towers identified and marked.
- ☑️ Rotor rotates clockwise when engine is cranked.
- ☑️ Wires attached: #1 to #1 tower, then 5,3,6,2,4 clockwise.
- ☑️ Timing set to 10° BTDC @ idle (vacuum line off).
- ☑️ Engine idles smoothly, no misfire.
❓ Frequently Asked Questions (Expanded FAQ)
Engine will run extremely rough, backfire through carbs, and lose almost all power. The firing order would become 1-5-3-6-4-2 – catastrophic misfire.
No. Electronic ignition (e.g., 280ZX distributor) still uses the same 1-5-3-6-2-4 order. The rotor and cap are identical in phasing.
If the engine backfires and won’t start but occasionally sputters, you might have the distributor installed 180° out. Check that rotor points to #1 when engine is at TDC compression (not exhaust).
Timing light, spark plug gapper, distributor wrench, 27mm socket for crank pulley, and a factory manual for L24 torque specs.
Indirectly, yes. Incorrect order can cause cross-firing and pre-ignition due to wrong cylinder firing at wrong time, leading to detonation.
Yes, Nissan L28 (2.8L) retains identical firing order 1-5-3-6-2-4 because it shares the same crankshaft design and cam profile family.
