Common Rail Injector Testing

1. 1Identify the injector return lines (spill rail) — usually a common rail or individual pipes.
2. 2Disconnect and route clear hoses from each injector return to separate containers.
3. 3Idle the engine for 30–60 seconds.
4. 4Compare the volumes — common rail injectors should return very little fuel at idle.
5. 5Any injector returning significantly more than the others is suspect.
6. 6On piezo injectors, even small differences can be significant.

Tools needed: Clear hose, containers, spanners

1. 1Disconnect the injector connector.
2. 2Measure resistance across the two pins.
3. 3Bosch solenoid: expect 0.3–1.0 Ω.
4. 4Delphi solenoid: expect 0.5–1.5 Ω.
5. 5Open circuit (OL) or short circuit (0 Ω) means the injector has failed.

Tools needed: Digital multimeter

1. 1Disconnect the injector connector.
2. 2Set multimeter to the MΩ range.
3. 3Measure across the two pins.
4. 4Expect 180 kΩ to 220 kΩ (varies by type).
5. 5Readings below 150 kΩ or above 300 kΩ indicate a faulty piezo stack.

Tools needed: Digital multimeter with MΩ range

1. 1Remove the injector from the engine (may require specialist extraction tool if seized).
2. 2Mount on a common rail injector test bench.
3. 3Test at rated pressure (e.g., 1,600 bar for Bosch CRI2).
4. 4Measure delivery quantity, return quantity, and spray pattern.
5. 5Compare to the manufacturer's published flow data.
6. 6Replace if delivery or return is out of specification.

Tools needed: Common rail test bench, extraction tools