NON-INVASIVE / PUMP

FUEL-PUMP CURRENT RIPPLE

Use pump current to compare commutator segments and calculate rotational consistency without opening the fuel system.

ESTIMATED SETUP3–5 min1 channel

WHY BEFORE DISASSEMBLY

CAPTURE THE SYSTEM
AS IT FAILED.

The waveform can reveal worn commutator segments, intermittent electrical contact and unstable pump speed before a tank or module is removed. It turns an invasive access decision into an evidence-based one.

Reading the signal

Good waveform

For a brushed pump at a steady operating point, current ripple repeats with fairly even commutation peaks and spacing. Interpret it with loaded supply voltage, fuel pressure and delivery volume.

Faulty waveform

Recurring missing or uneven segments can suggest brush or commutator wear. A changed average current or repetition rate can also reflect supply loss or hydraulic loading. Brushless pumps require a different interpretation; do not count their supply ripple as commutator segments.

Common mistakes

AVOID THE
FALSE CLUE.

Testing with the connector unplugged when the fault only appears under load.
Using a generic voltage value instead of the vehicle-specific specification.
Skipping power, ground and reference checks before condemning the component.
Moving the harness or clearing codes before capturing the original evidence.
Replacing a part without repeating the test.

PREPARE THE TEST

✓ Identify the correct pump feed conductor✓ Zero the clamp away from magnetic fields✓ Command the pump with a scan tool when supported✓ Observe fuel-system fire precautions

STEP-BY-STEP PROCEDURE

Clamp around the single pump feed wire at an accessible fuse-box or harness location.
Set the range to display average current and the smaller commutator ripple riding on it.
Command the pump on or capture it during prime, crank and run.
Freeze a stable section and compare successive current humps for height and spacing.
Calculate pump speed only when the number of commutator segments is known.
Verify pressure, volume and retained pressure before condemning the pump; a clean current pattern does not prove hydraulic performance.

WHAT THIS TEST CANNOT PROVE

Brushless, pulse-width-controlled and multi-speed pumps produce different signatures. Pressure and volume remain separate tests.

⚠ SAFETY / CONNECTION CAUTION

Do not pierce sealed fuel-tank wiring near vapors. Follow approved fuel-system safety and use fused test leads where appropriate.

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.

NEXT QUICK TEST / INJECTInjector Voltage + Current→