A rough idle on an LB7 Duramax most often points to the engine's known weak spot: the injectors.
What causes rough idle on the LB7 Duramax
- Cracked or leaking injectors (the LB7's known issue)
- Uneven injector balance rates
- Air or water in the fuel
- A weak fuel supply
How to diagnose it
Read the injector balance rates - an out-of-line cylinder points to a leaking injector. Because the injectors are under the valve covers and share the same life, verify which are bad before deciding.
The fix
Replace the failing injectors - most owners do the full set since the labor to reach them is significant. Confirm clean fuel and healthy supply pressure to protect the new set.
Frequently asked questions
Why does my LB7 idle rough?
Most often a leaking injector. Balance rates confirm which cylinder is off.
Should I replace all eight injectors?
Usually yes - the labor is significant and all eight have lived the same life.
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