Diesel Rough Idle, Knocking or Misfire: Is It the Injectors?

If your diesel shakes at idle, knocks more than it used to or feels uneven when you pull away, one or more injectors may no longer be delivering the same amount of fuel as the others. There are other possible causes too, so it is worth checking before you buy parts.

Signs that point to the injectors

Shaking at idle that eases when you rev the engine
Louder knocking than normal, sometimes from one cylinder
Misfire or engine warning light, with injector or cylinder fault codes
Loss of power, or higher fuel use than before
Smoke under acceleration
Fuel smell or a diesel leak around the top of the engine

Other causes to rule out

A worn dual-mass flywheel or engine mounts can make the car shake at idle. A sticking EGR valve, air leaks and low compression can also cause rough running. A diagnostic check helps narrow it down. Many modern diesels show injector correction values on a diagnostic tool, and one injector that is well out of line with the others is a useful clue.

Should you replace one injector or all of them?

That depends on the test results. All the injectors in an engine have done the same mileage, so if one has failed it makes sense to test the others. You may only need to deal with the ones that are out of specification. Testing first means you do not pay for parts you do not need.

Can you keep driving with a bad injector?

It is best not to leave it. A leaking injector can put extra fuel in the cylinder, and that can damage the engine or load up the diesel particulate filter. If the car is misfiring badly, smoking heavily or smelling of fuel, have it checked before you drive far.

Testing and reconditioning in Dublin 15

We test common rail injectors on dedicated test benches and recondition them to specification where possible. We can also supply new injectors from brands such as Bosch, Denso, Delphi and Continental. Testing starts from €80 and injector reconditioning from €140. Reconditioned parts have a 1-year, parts-only, unlimited mileage warranty.

Garages and fleet managers are welcome as well as private owners.

Call 085 200 9922 or request a quote. Diesel Injector Repair, Unit 6, 1st Floor, Old Quarry Campus, Blanchardstown, Dublin 15, D15 HX03.