Repair
5 signs your diesel injectors are going bad
The five symptoms that point at injectors, and the harness and fuel-supply problems that can look exactly the same.
Injectors get blamed for a lot. Sometimes they deserve it. Before anyone quotes you a full set, it helps to know what injector trouble looks like and what can fake it.
1. Hard starts
A truck that cranks and cranks, cold or after it sits, can have an injector that won't hold pressure or leaks back. It can also be air getting into the fuel lines, which is common on older Duramax trucks with a leaking filter head.
2. White smoke at startup or idle
Unburned fuel shows up as white smoke. One injector sticking open or spraying badly can do it on its own.
3. A rough idle or a miss
A shake at idle, or a miss you can feel through the seat, often traces back to one cylinder getting the wrong amount of fuel.
4. Knocking
A sharp knock that wasn't there last month deserves attention before it gets louder. Injector trouble is one cause. It isn't the only one, so it's worth finding out which before parts get ordered.
5. The oil level goes up
If the dipstick reads higher between oil changes, fuel is getting into the oil and thinning it. It's easy to miss, because a rising level doesn't look like a problem. On an LB7 Duramax it's a classic injector sign.
What can fake injector trouble
A few problems produce the same symptoms, and they cost a lot less than injectors:
- A chafed injector harness. On an LLY Duramax this is common enough to check first.
- A weak lift pump or a clogged fuel filter starving the system.
- Air in the lines after a filter change.
That's why we test before we quote. Replacing good injectors doesn't fix a harness.
Engines where injectors come up most
LB7 Duramax injectors are the best-known case. The 5.9 common-rail Cummins is hard on injectors when the fuel is dirty. On a 6.0 Power Stroke, sticking injectors are tied to oil quality, so the oil gets checked too.
