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Bad diesel injector symptoms — and how we test them

A failing diesel injector shows as rough idle, white or black smoke, a miss under load, fuel in the oil, hard starts or a cylinder-balance code. Diesel Fuel Injection Service in Scappoose, Oregon flow-tests injectors on the bench, reports which ones are out of spec, and supplies tested reman or new injectors for Cummins, Duramax, Power Stroke, Sprinter and heavy-duty engines. (503) 235-1947.

Symptoms by failure

  • Leaking nozzle: white smoke at idle, rough cold start, diesel smell in the oil
  • Stuck or worn: miss or knock on one cylinder, cylinder-balance or contribution codes
  • Return flow high (common rail): low rail pressure, long crank, stalling warm
  • Carbon-fouled nozzle: black smoke, lost power, poor economy

How we test

  • Pop and spray pattern on mechanical injectors
  • Return-flow, leak-down and delivery on common-rail injectors, compared to the maker's spec
  • A written report per injector so you replace what failed, not the whole set by guess

Questions

If the set has the same hours and one failed from wear, the rest are close behind; if one failed from debris or a single fault, replace one and fix the cause.

Yes — pack them capped and dry; we test, report and quote.

Cummins 5.9 / 6.7, Duramax LB7 through L5P, Power Stroke 6.0 / 6.4 / 6.7, Sprinter OM642 and most heavy-duty engines are in stock or a day away.

Usually fuel quality or a lift pump that starved the system; we tell you what the injectors show so the new set lasts.