COMPARE / INJECT

INJECTOR VOLTAGE + CURRENT

Correlate injector driver voltage with coil current to prove command, winding behavior and mechanical opening clues.

ESTIMATED SETUP3–5 min2 channels
WHY BEFORE DISASSEMBLY

CAPTURE THE SYSTEM
AS IT FAILED.

Resistance testing requires disconnection and may miss a winding that fails hot. A live current-and-voltage capture compares cylinders under the complaint condition before the rail or injector is disturbed.

Reading the signal

Good waveform

On an identified solenoid injector, the voltage command and current rise align consistently. Current limiting and turn-off behavior match the driver design. A subtle change associated with pintle movement may be visible on some injectors, but is not universal.

Faulty waveform

No current during a verified command can indicate an open circuit or missing feed. An unusual ramp or early current limit can point to circuit, coil or supply problems. Correct electrical operation does not prove fuel flow or sealing; compare with balance, pressure and leakage tests. Piezo injectors use a different charge/discharge strategy.

Common mistakes

AVOID THE
FALSE CLUE.

PREPARE THE TEST

✓ Identify port, direct or peak-and-hold control✓ Confirm scope and probe voltage ratings✓ Backprobe without spreading terminals✓ Use the same scale for cylinder comparisons

STEP-BY-STEP PROCEDURE

  1. Connect the current clamp around one injector conductor. Connect the voltage channel to the control circuit using the correct ground or differential method.
  2. Start with enough voltage range to contain the inductive turn-off spike.
  3. Run the engine at the condition that produces the symptom and capture several events.
  4. Measure on-time, current rise, peak/hold levels and turn-off behavior.
  5. Where the injector design produces one, locate the small change in current slope associated with pintle movement.
  6. Overlay or repeat the capture on other cylinders using identical settings. Confirm electrical evidence with balance, pressure or contribution testing.
WHAT THIS TEST CANNOT PROVE

Not every injector displays a visible pintle hump. GDI and piezo systems require specialized procedures and correctly rated equipment.

⚠ SAFETY / CONNECTION CAUTION

Direct-injection circuits may use hazardous voltage and fuel pressure. Do not apply ordinary port-injector procedures to GDI or piezo systems.

STOP BEFORE CONDEMNING THE PART

Repeat the capture, verify the circuit under load and use vehicle-specific specifications. Follow with the most direct confirmation test indicated by the evidence.

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