The Lexus IS250 uses a 2.5-liter V6 engine, and its standard ignition firing order is 1-2-3-4-5-6, with cylinders numbered 1 through 6 from the front of the engine. The exact sequence can vary by engine code and model year, so check the factory service manual for your car.
Engine layout and cylinder numbering
Understanding the two-bank V6 layout helps explain how the firing order maps to cylinder numbers. On most IS250 engines, cylinders are split into two banks with three cylinders each.
Before we list the cylinder numbers and the firing sequence, note this arrangement helps tune the engine for smooth idle and balanced firing across banks.
- Bank 1 comprises cylinders 1, 3, and 5.
- Bank 2 comprises cylinders 2, 4, and 6.
With this numbering scheme, the engine's firing order is designed to evenly stagger the ignition events between banks to minimize vibration and optimize valve timing interactions.
Firing order sequence
Using the standard two-bank numbering for the IS250's V6, the ignition sequence most commonly used is a six-step order that alternates between banks. The sequence is typically described as follows:
- Cylinder 1 fires
- Cylinder 2 fires
- Cylinder 3 fires
- Cylinder 4 fires
- Cylinder 5 fires
- Cylinder 6 fires
Depending on the exact engine code or production year, there may be minor variations in the sequence. Always verify with the official service information for your specific vehicle.
Maintenance implications and checks
Knowing the firing order matters when diagnosing timing, misfires, or when replacing spark plugs and ignition coils. The IS250 uses coil-on-plug ignition in most variants, so each coil's position corresponds to its cylinder number and firing event.
When replacing spark plugs or diagnosing misfires, ensure you reference the correct cylinder mapping for your model year and engine code. An incorrect wiring harness or misrouted ignition coil wiring can result in rough idle or misfires.
In summary, the IS250's six-cylinder firing order follows a 1-2-3-4-5-6 sequence with a two-bank numbering system (1,3,5 on Bank 1 and 2,4,6 on Bank 2). Always confirm against your vehicle's factory documentation.
Summary
The Lexus IS250 uses a 2.5L V6 with a standard 1-2-3-4-5-6 firing order, distributed across two banks (Bank 1: 1,3,5; Bank 2: 2,4,6). Verify against your specific engine code and year in the factory service manual to ensure accuracy during maintenance or repairs.