How to

Testing a fuel pump with scope testing

Share Resource:

Resource Highlights

In this article, you will find out about how to test a fuel pump with scope testing.

How to Resource Banner
Diagnostics & Test Equipment How to 1 min read

Fuel pressure and volume tests are not always conclusive regarding the condition of the fuel pump. Some fuel pumps will pass these tests and yet cause an intermittent starting problem. This condition is typically the result of a worn commutator bar on the armature. If the pump motor stops at that particular spot when the engine is turned off, current will not flow between the brush and commutator the next time the pump is activated. In some cases, tapping the fuel tank may create enough of a vibration to get the pump working.

Using a lab scope is the best way to evaluate the condition of a fuel pump. Even slight inconsistencies will show up in a waveform that took milliseconds to record. By analyzing a fuel pump waveform, you can quickly identify problems that would otherwise go undetected using conventional pressure and volume tests. A good fuel pump waveform consists of a series of small uniform humps. Examining the current waveform of each commutator bar during a complete rotation of the fuel pump will give an accurate indication of the internal condition of the fuel pump. Any spikes indicate problems with the brushes and/or commutator segments.

The scope also displays the average current. It is normal for a fuel pump current to be higher when the pump is first energized and begins to push fuel, though the amperage should quickly drop and stabilize. Low current readings are indicative of electrical problems, such as brush and commutator wear, a poor ground, or high-resistance connections. Excessive fuel pump current indicates that the pump is being overloaded. This may be the result of a restricted fuel filter, a clogged strainer, or blocked return line. Check the appropriate service manual for fuel pump current specifications.

SIGN UP TO FIND MORE

Fill yp your details to hear more from our experts and get the latest updates from Delphi.

I have read and accept the <a href="https://www.delphiautoparts.com/gbr/en/terms-conditions">Terms of Use</a> and <a href="https://www.delphiautoparts.com/gbr/en/privacy-policy">Privacy Policy</a>

I agree to receive personalised marketing emails.

I would like to be kept up to date with promotions/marketing/features/events.

You can change your mind at any time by clicking the unsubscribe link in the footer of any newsletter email you receive from us, or by contacting us at <a href="[email protected]">[email protected]</a>

A mechanic holding a diagnostic tool

Diagnostics

Discover our extensive range of OE-level diagnostic and test equipment for quicker, more accurate servicing and repairs.

Two mechanics ready to start training

Training

Choose from our expert-led, accredited training courses to enhance your skills and prepare you for the vehicles of tomorrow.

where to buy

Find out where to buy Delphi parts

where to repair

Find your nearest Service & Diesel Centres

Select your Region