Bad diesel injector symptoms include rough idle and misfires, hard starting, black or white smoke, a knock or loud clatter from one cylinder, loss of power, higher fuel consumption and, on many engines, fuel in the oil or excessive return flow. Injectors fail by sticking open or closed, leaking from the tip, wearing internally so they return too much fuel, or leaking at their seals and washers.
Symptoms and what they suggest
| Symptom | Likely injector fault |
|---|---|
| Black smoke under load | Poor spray pattern or dripping tip; see diesel black smoke |
| White smoke, raw fuel smell | Unburned fuel from a weak injector or low compression; see diesel white smoke |
| Knock or harsh clatter on one cylinder | Injector stuck open or over-fueling; see diesel knocking |
| Rising oil level, fuel smell in oil | Leaking injector or seal on engines with internal fuel lines |
| Hard starting, low rail pressure | Excessive return flow; codes such as P0087 |
| Combustion gases in the fuel or coolant | Leaking injector cup or seal |
Seal and washer leaks
A leaking copper washer under the injector lets combustion gases escape, often with a ticking sound, black soot around the injector, and fuel smell. Leaking O-rings or seals can let fuel into the oil. These are cheaper to fix than the injector itself, but they need attention before they damage the head or wash down the cylinder.
Fuel in the oil
On engines where the injectors sit under the valve cover, a leaking injector body or seal can drip fuel into the crankcase. The oil level rises between changes, the oil smells of diesel, and the thinned oil protects bearings poorly. Check the level often and act quickly if it climbs.
Testing
- Read codes and look at injector balance rates or contribution data with a capable scan tool.
- Run a return-flow (leak-off) test on common-rail engines.
- Perform a cylinder cutout test to find the cylinder that changes least.
- Check the oil level and smell for fuel dilution.
Dirty injectors
Poor fuel, water and lack of filter changes cause most injector problems. Some deposits can be reduced with a quality fuel treatment, but worn or damaged injectors must be replaced. Keep up with filters and water separator draining; see fuel filter and diesel lift pump.
Replacing injectors
Common-rail injectors are often coded to the engine computer and need their codes entered after installation. Replace seals and washers with every injector, and torque to specification. If the high-pressure pump has failed and sent debris through the system, the injectors may need replacing with it; see CP3 pump and CP3 vs CP4.
Related
See fuel injector symptoms on gas engines, diesel losing power and our 6.7 Cummins engines.
More guides: water in diesel fuel.
Trouble codes: P0088 Fuel Rail Pressure Too High · P0201 Injector Circuit Cylinder 1 · P2263 Boost System Performance · P0263 Cylinder 1 Contribution/Balance · P0266 Cylinder 2 Contribution/Balance · P0269 Cylinder 3 Contribution/Balance · P0272 Cylinder 4 Contribution/Balance · P0275 Cylinder 5 Contribution/Balance · P0278 Cylinder 6 Contribution/Balance · P0093 Fuel System Large Leak · P0094 Fuel System Small Leak · P0611 Injector Control Module Performance · all OBD2 codes.
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