1987 Jeep Cherokee LimitedFACTORY OEM SERVICE PROCEDURE

Fuel Injection System - Diesel: Testing: Injectors

  1. Remove injectors from engine. Check injectors for erosion (due to unfiltered air particles), carbon build-up, or Blue-colored tip (caused by excessive engine heat). Replace any damaged injectors as necessary.
  2. Fill reservoir of Bosch Nozzle Pressure Tester (EFEP60H) with clean test oil. Connect injector and holder assembly to tester. Close pressure gauge valve. Quickly operate tester lever 8-10 times to bleed air from tester.
    CAUTION: DO NOT  allow test oil to be sprayed onto hands or fingers while testing. High pressure from nozzle spray can penetrate skin, which could cause blood poisoning.
  3. Open pressure gauge valve 1/4 turn. Slowly operate tester (one pump/second), noting pressure required to open nozzle. Nozzle opening pressure should be 1885-2001 psi (133-141 kg/cm2 ). Injectors with incorrect opening pressure should be replaced.
  4. Slowly operate tester and note spray pattern of each injector. Spray should emerge at a straight angle, and should have an even, finely atomized pattern. Replace any injectors that do not have correct spray pattern. A "whistling" sound, produced during testing, is a normal condition.
  5. Slowly operate tester until pressure reading is 290 psi (20 kg/cm2 ) below normal opening pressure. Hold pressure at that point for 10 seconds. No fuel should drip from nozzle. If leakage occurs during 10 second period, replace injector. A slight wetting of nozzle tip is normal.
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When to See a Mechanic

Stop DIY work and contact a certified mechanic immediately if any of the following apply:

  • • You smell fuel, burning insulation, or see smoke.
  • • Brakes feel soft, pull hard to one side, or make grinding noises.
  • • The engine overheats, stalls repeatedly, or misfires under load.
  • • You are missing required tools, torque specs, or safe lifting equipment.
  • • You are not confident in the next step or safety outcome.

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