Loss of power on a 6.7L Cummins usually comes from the air side (turbo/boost), the fuel side (supply pressure), or the emissions system going into a protective mode.
What causes loss of power on the 6.7L Cummins
- A sticking VGT or boost leak (underboost)
- Low fuel supply pressure (weak lift pump)
- A clogged air or fuel filter
- Emissions/DPF restriction triggering derate
- Worn injectors
How to diagnose it
Check for boost leaks and confirm the VGT builds boost; measure fuel supply pressure; inspect the air and fuel filters. Pull codes to see if an emissions derate is active.
The fix
Fix a boost leak or sticking VGT, restore fuel supply pressure with a healthy lift pump, replace clogged filters, and address any emissions restriction. Clean air and fuel plus healthy boost restore power.
Frequently asked questions
Why is my 6.7L Cummins down on power?
Most often underboost (VGT/boost leak) or low fuel supply pressure. Check both, plus the air and fuel filters.
Can a lift pump cause power loss?
Yes - low supply pressure starves the high-pressure pump and costs power.
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