EJ20 Firing Order: 1-3-2-4 Encyclopedia | Boxer Precision
Subaru EJ20 Firing Sequence: 1 → 3 → 2 → 4 (continuous loop)
Cylinder layout: Left bank (front to rear): #1 → #3 Right bank: #2 → #4
Visualization: orange glow indicates active ignition. Each firing step occurs at 180° crank intervals.
📐 Why 1-3-2-4? The Engineering Behind Subaru’s Choice
The EJ20 engine uses a flat-plane crankshaft with crankpins positioned 180° apart. The firing order 1-3-2-4 ensures that the power strokes occur every 180 degrees of crankshaft rotation (even firing). This provides:
- Perfect primary balance: Pistons #1 and #2 move outward together, #3 and #4 move inward together, canceling first-order vibrations.
- Reduced torsional stress: Evenly spaced combustion pulses minimize crankshaft twisting.
- Optimal scavenging: The exhaust pulse timing works with unequal-length headers to create the signature Subaru rumble while maintaining cylinder-to-cylinder consistency.
- Lower bearing loads: Connecting rod journals experience symmetrical loading, extending engine life.
If you compare with an inline-four using 1-3-4-2, the flat engine would produce a severe rocking couple if 1-3-4-2 were applied. Subaru engineers specifically designed the crankshaft throw pattern (cylinder #1 and #2 share the same crankpin orientation, #3 and #4 share the opposite orientation) to match 1-3-2-4.
| Cylinder # | Location (driver’s perspective) | Crank Angle (degrees) | Firing Position |
|---|---|---|---|
| #1 | Left front (near timing cover) | 0° | 1st |
| #3 | Left rear (firewall side) | 180° | 2nd |
| #2 | Right front | 360° | 3rd |
| #4 | Right rear | 540° | 4th |
🔧 How to Check & Verify EJ20 Firing Order – Professional Guide
Whether you’re troubleshooting a misfire or rebuilding an EJ20, verifying the ignition sequence is critical. Follow these steps:
- Identify cylinder numbers – Use the table above. Mark plug wires if needed.
- Inspect ignition leads or coil pack: On distributor-type EJ20s (early), the cap should have terminals arranged in order: 1,3,2,4 clockwise. On coil-on-plug (COP) engines (EJ205/EJ207), the ECU firing order is hardcoded; but check wiring harness continuity.
- Use a timing light: Connect inductive clamp to #1 plug wire. The light should flash at consistent intervals. Then move to #3, #2, #4. They must flash in 1-3-2-4 sequence.
- Perform a power balance test: With engine running, momentarily ground each cylinder’s ignition signal (or use injector kill) – the RPM drop should follow the 1-3-2-4 pattern if order is correct.
- Consult ECU live data: Using OBD2 scanner (on OBD2 EJ20), monitor misfire counters. P0301 = cylinder #1, P0303 = cylinder #3, etc. Consistent with firing order helps diagnosis.
✅ Advantages of 1-3-2-4 Firing Order
- Butter-smooth operation – no balance shafts needed.
- High RPM capability – EJ207 revs safely to 8000+ RPM.
- Reduced vibration fatigue on engine mounts and accessories.
- Predictable exhaust tuning – enables twin-scroll turbo setups.
- Lower crankshaft mass – improves throttle response.
- Simpler ignition timing mapping – even cylinder pressure distribution.
⚠️ Disadvantages & Considerations
- Confusion for beginners – many assume inline-4 order.
- Complex spark plug access – boxer layout requires removing air intake or intercooler.
- Exhaust manifold complexity – unequal-length design needed for rumble, but can cause cylinder-to-cylinder EGT variation.
- Not interchangeable – mixing with other firing orders destroys engine.
- Aftermarket ECU configuration – must set cylinder sequence to 1-3-2-4; wrong setting leads to misfire.
🛡️ Is It Safe to Change the EJ20 Firing Order?
Absolutely NOT safe without complete internal redesign. The EJ20’s crankshaft counterweights, camshaft lobes, and ECU ignition timing maps are engineered exclusively for 1-3-2-4. Any alteration (e.g., swapping plug wires to 1-2-3-4) will cause:
- Catastrophic engine knock / detonation
- Bent connecting rods or damaged bearings
- Intake backfires (risk of fire)
- Immediate catalytic converter meltdown
- Uncontrollable engine vibration
Even aftermarket standalone ECUs require the firing order to be set to 1-3-2-4 and the cylinder numbering to match the stock configuration. There is no performance benefit to changing the order; it’s a physical constraint of the crankshaft design.
🏁 Advanced Use: Tuning & Diagnostics Related to Firing Order
Professional tuners rely on the 1-3-2-4 firing order to calibrate ignition timing per cylinder. On EJ20 engines, individual cylinder timing correction (via ECU like Link G4+ or Haltech) can be applied to balance EGTs. Moreover, the firing order affects knock detection: knock sensors are positioned to differentiate cylinder #1 vs #3 events. When data logging, the crank trigger pattern (36-2-2-2 or 6+7 teeth) aligns with the firing order. Understanding the order helps diagnose intermittent misfires and coil driver failures.
⚙️ Crankshaft Phasing & Firing Order Interaction
The EJ20 crankshaft uses a “flat” arrangement where cylinders #1 and #2 share the same crankpin phase (0°), while cylinders #3 and #4 share the opposite phase (180°). This is why the firing order must alternate between banks: 1 (left front) → 3 (left rear) → 2 (right front) → 4 (right rear). This results in a firing interval of 180°, 180°, 180°, 180° – perfectly even. By comparison, a crossplane inline-four has 180°-180°-180°-180° as well but with different cylinder pairing. The boxer design’s low center of gravity combined with this order makes the EJ20 one of the smoothest 4-cylinders ever made.
