Onan
Rich Fuel Mixture / Incomplete Combustion (Diesel or Gas)
Generator emits excessive black smoke from exhaust during operation
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Safety Warning
This repair may involve working with high voltage components or water connections. Always unplug the appliance before removing any panels.
If you are not confident in your ability to perform this repair safely, we strongly recommend contacting a professional technician.
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Possible Causes
Clogged air filter restricting airflow, Overfueling due to injector or carburetor issues, Turbocharger problem (if equipped), Overloading the generator
How to Fix / Troubleshooting
Safety first: Operate in a well-ventilated area. Avoid breathing exhaust fumes.
- Check air filter: Remove and inspect the air filter element. Replace if dirty or restricted with an Onan-approved filter.
- Reduce load: Open the main breaker and restart. Gradually add load and keep within rated capacity. Excessive load can cause black smoke.
- Fuel system inspection: On diesel units, have injectors tested and serviced if smoke persists. On gas units, inspect carburetor for stuck choke or flooding.
- Turbocharger (if equipped): Inspect intake and exhaust connections for leaks and ensure the turbo spins freely. Turbo issues require professional service.
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Repair Difficulty
Hard
4/5
Required Part
Air Filter Element
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