How Much Current Does A Fuel Pump Draw

Last calendar month, we explained how to use voltage driblet testing to determine whether an electrical fuel pump is receiving adequate supply voltage for proper performance. This month, we'll explain how to use an inductive depression-amp probe and a digital storage oscilloscope (DSO) to expect inside an electric fuel pump and assess its health

Inductive amp probes come in all shapes and sizes, and they tin can handle the full range of currents-both AC and DC. A low-amp inductive probe can be used to measure out the relatively low current period (ordinarily below 10 amps) in a fuel pump circuit.

The anterior probe converts the signal into one that can be understood by the voltage-reading DSO. The DSO will notwithstanding be thinking information technology's seeing volts, but we'll know they're amps.

Nearly low-amp probes have two settings-10mV/A and 100mV/A-and they touch the style the fuel pump waveform is displayed on the DSO screen. If the probe is fix on the 10mV/A scale, for each 10mV displayed on the DSO, the probe is measuring 1 amp of current. If the probe is assault the 100mV/A calibration, for each 100mV displayed on the DSO, the probe is measuring 1 amp.

When viewing fuel pump current waveforms on your DSO, offset with a time base of operations of either 1 or 2mS per division, and a voltage scale of 100mV per sectionalisation. The waveform can be analyzed in greater detail at 1mS per division, while the rotational speed of the fuel pump can be more than easily calculated at 2mS per division.

Adjust the scope and probe to the settings above, then use the anterior probe'southward Goose egg dial to motion the waveform to the 0 volt (ground) position on your DSO before clamping the probe around the fuel pump wiring.

The amp probe clench tin be placed at whatsoever bespeak in the fuel pump circuit, every bit long every bit it's in series between the voltage supply and the ground for the load. Clamp the probe to one of the pump wires, if it's accessible. Or clamp information technology around the pump'south power wire at the fuse box, at a relay or inertia switch or at an underhood test connector.

fuel pump amperage draw

While voltage may exist different at various points in a circuit, current in a series circuit is the aforementioned at all points. So brand sure there are no additional components, similar a transfer pump, wired in parallel to the master pump, as these will affect the examination results.

The engine and other electrical components must non be running while the fuel pump is being tested, equally they may affect the bachelor voltage to the pump, which will also impact its amperage readings. Some manufacturers provide a separate underhood pigtail test connector to power the fuel pump. Others identify a fuel pump test pin in the diagnostic connector. To operate the fuel pump with the test connector and the engine OFF, connect a powered jumper lead to the connector.

Check the wiring diagram before using this method. You may be bypassing the fuse, relay or other switching component when power is provided to the pump via an external source. If then, the pump current describe may be within specifications during the pigtail test. But a voltage drop in the bypassed circuit could crusade depression electric current at the pump during normal vehicle operation. Ideally, the fuel pump should be powered ON using the same wiring that's used during normal performance.

A skilful pump will produce a pattern similar to the one shown here. The telescopic is gear up to 100mV per division and the probe is on the 100mV/A calibration. Each vertical sectionalization is equal to 1 amp, so the pump is drawing between 5 and 6 amps.

If the pump is good, the waveform humps should be uniform. Poor contact between the brushes and one or more of the commutator segments volition produce jagged or low-aamplitude humps.

Mechanical resistance within the pump can issue in higher-than-normal average pump electric current. A clogged fuel filter or fuel line restriction will also increase pump current. Electrical resistance, either in the pump or elsewhere in its circuit, lowers bachelor pump voltage and reduces pump current.

High-pressure level pumps, similar those in port fuel injection (PFI) systems (35 to 45 psi), require more than current than depression-pressure pumps in throttle body injection (TBI) applications (9 to 13 psi). A TBI pump may have a normal current describe every bit low as 3 to five amps, with PFI pumps pulling four to 6 amps on average. A GM central point injection (CPI) pump (55 to 64 psi) needs 8 to 10 amps.

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