How to test a fuel pump with a digital multimeter

How To Test A Fuel Pump With A Digital Multimeter

Your car has a lot of components that have to work together to drive from one point to another.

Luckily, each of these components in itself isn’t that hard to understand, and the better you can identify where car problems may lay, the easier it will be to solve them. 

One of the small components that connect two big parts in your car together is the fuel pump. As the name indicates, the fuel pump is responsible for getting the fuel that’s in your gas tank to your engine that ultimately powers the car.

fuel pump

A faulty fuel pump means that you’re not getting (enough) fuel to the engine. You may notice problems with accelerating, especially at high speed, and other signals of your car struggling to get the power it should have.

In the blog post below, we’ll take a look at what to do when your fuel pump is having issues, and how a digital multimeter can help you find (and then fix) the issue.

Possible problems with your fuel pump

There are two main parts of your fuel pump that can actually have a problem. The first is the pump itself, and the second is the fuel pump fuse, which is responsible for supplying the fuel pump with power.

As you might imagine, the fuel pump fuse is the easiest to diagnose using a digital multimeter (I use Fluke 87-v multimeter which you can check on Amazon.com). A blown fuse will prohibit the fuel pump from working, just because the fuse is unable to power it. We’ll discuss how to test a fuse in more detail below.

If the fuse isn’t the problem, you’ll have to test the fuel pump itself. The pump can either be broken, the filter might need replacing, or you could have a loss of fuel pressure.

To diagnose a broken pump, we need the digital multimeter again. Just like with the fuse, we’ll go into further detail about how to check a fuel pump with a digital multimeter in a little while.

Voltage drop test

Aside from the standard tests that come with a digital multimeter, problems with your fuel pump could require you to perform a voltage drop test. This test requires some more knowledge than selecting the right dial on your multimeter and plugging in the leads.

A voltage drop is the result of high resistance. This usually means that one of your wires is corroded, prohibiting the flow of electricity. Resistance is usually measured in Ohms, but because this requires knowing where the problem is, or taking everything apart to measure individual components, a voltage drop test can be a lot easier.

To perform a voltage drop test, first test the voltage of the car battery. This should always be around 12 V. Now, move your test leads to the area you want to test (in this case, the fuel pump). If you see a difference of more than 0.5V, you have a significant voltage drop.

How to test a fuel pump with a digital multimeter

Your first step to testing a fuel pump with a digital multimeter is to test the fuse. With most fuses, you’ll be able to see when it’s defect. Check for a broken or ‘burned’ look. If you can’t see anything wrong with the fuse, but you want to be sure, you can use your multimeter.

Set the meter to the resistance setting (usually shown with a Ω symbol) and put the two leads together first. Now, put a test lead on each end of the fuse. If the fuse is fine, your reading should be exactly the same as without the fuse. If the fuse is broken, you will get no reading, or the multimeter will indicate that there’s an ‘open loop’ (O.L.).

If the fuse test comes back negative, you should move on to the fuel pump itself. Perform a voltage drop test like described in the previous section to make sure the fuel pump isn’t the problem. If the fuse and the fuel pump tests come back negative, take a look at the filter. If too much residue built up in the filter, it can limit the performance of the fuel pump.

Finally, you can check the fuel pressure. This will require a fuel pressure meter, which normally costs $20-$30. If you work on cars regularly, this may warrant the purchase, but otherwise, it may be time to pay a visit to the car shop.

Conclusion

Now that you know how to test a fuel pump with your multimeter, it’s time to put your knowledge to the test.

It’s important to be familiar with your multimeter and its functions, so it might be a good idea to test a fuse and perform a voltage drop test before it’s actually a problem.

Leave a Comment

Your email address will not be published. Required fields are marked *