Black smoke from a 6.7L Cummins means too much fuel or too little air - an air-side restriction, a boost problem, or over-fueling injectors.
What causes black smoke on the 6.7L Cummins
- A clogged air filter or intake restriction
- A boost leak or underboosting VGT (not enough air)
- Worn or over-fueling injectors
- A dirty or restricted intake/EGR
How to diagnose it
Check the air filter and intake first, then look for boost leaks and confirm the VGT is building boost. If air is fine, test the injectors for over-fueling.
The fix
Replace a clogged air filter, fix boost leaks, service a sticking VGT, and replace worn injectors. Restoring the air-fuel balance clears the smoke and restores economy.
Frequently asked questions
What causes black smoke on a 6.7L Cummins?
Too much fuel or too little air - a clogged air filter, boost leak, or over-fueling injectors. Start with the air side.
Is black smoke bad?
It signals an air-fuel imbalance that wastes fuel and can foul the emissions system. Diagnose the cause.
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