Cylinder 1 Contribution/Balance

Possible causes

• CommonWorn, leaking or partially blocked injector on cylinder 1
• CommonLoss of compression on cylinder 1 - worn rings, a burnt valve, a head gasket
• CommonWorn spark plug or failing coil on cylinder 1, on a petrol engine
• CommonInjector correction values not written after replacement, on a common-rail diesel
• PossibleVacuum or intake leak affecting that cylinder
• PossibleCamshaft lobe wear on cylinder 1

What you might notice

• Rough running, worse under load
• Loss of power
• Poor fuel economy
• Smoke from the exhaust on a diesel
• Vibration at idle
• Check engine light on

What to check, in order

1. Read all codes. A misfire code for cylinder 1 alongside this one narrows it down; this code without one usually means a weak cylinder rather than a dead one.
2. On a common-rail diesel, ask whether injectors have been replaced and whether their correction codes were written to the module. Each injector is supplied with calibration values, and fitting one without entering them produces exactly this - it is one of the most commonly missed steps in a diesel injector job.
3. Compare fuel return flow across the injectors on a diesel. A leaking injector returns far more than its neighbours and shows itself immediately.
4. Test compression on cylinder 1 if fuel and ignition both check out. A mechanically weak cylinder is the remaining explanation and no amount of injector work will fix it.
5. On a petrol engine, check the spark plug and coil for cylinder 1 first - they are far cheaper to eliminate than an injector.