Symptoms of a Bad Fuel Pump and What Causes Them

Fuel is an essential part of the equation we call fuel/air mix. Without fuel, there is no combustion. The job of delivering fuel to the engine is an important one, which is why fuel pumps are one of the key components of every car. A fuel pump draws or pumps fuel out of the fuel tank and feeds it to the engine via a network of fuel lines. 

Needless to say, a bad fuel pump can greatly affect the performance of an engine, or even bring it to a complete halt. Today we’ll discuss various symptoms of a bad fuel pump and what causes them.

Article updated on 01/04/22. Original publishing date 03/10/21.

Types of Fuel Pumps

While there are two main types of fuel pumps – mechanical and electric, the former is obsolete, and it’s only the latter that you’ll find in modern vehicles. Electric fuel pumps are not only simpler and more reliable but also better at maintaining a specific pressure. This is important since modern engines require reliable and consistent fuel pressure in order to fine-tune the fuel trim as you drive the car. 

Electric fuel pumps are further divided into two types – in-tank and external. Their names give away their biggest difference. The former is mounted inside the fuel tank, while the external one is positioned outside the tank. An external fuel pump is almost always located quite close to the fuel tank as it still works by pushing the fuel and not pulling it.

Symptoms of a Bad Fuel Pump

A consequence of the important role of the fuel pump is that any discrepancy in performance will be in view. Here’s a list of the common symptoms of a bad fuel pump.

Fuel Pump Not Priming

We’ve listed this one first because this is the most obvious symptom. It’s also one of the easiest to diagnose as the engine won’t turn over and, in many cases, you’ll hear that it’s not priming like it usually does at startup. You can hear the pump turn on for a few seconds when you turn the ignition to the accessory position in most cars. 

If the priming wasn’t audible in your car, to begin with, you could give the connectors a once-over with a multimeter. If the fuel pump is at the receiving end of sufficient voltage, and it’s still not working, there’s most likely something wrong with it.

However, if the fuel pump isn’t being supplied with adequate current, it’s not the fuel pump that’s at fault. It could be either an issue with the fuse or the relay and these would be the easiest to fix. All that would be required in this case would be a replacement fuse or relay, and you would be good to go.

There’s also a possibility of there being an issue with the inertia switch. Often times the baggage in a trunk cab hit the inertia switch and disconnect the supply from the fuel pump, which in turn would result in the fuel pump not priming. Like the aforementioned issues, this too is an easy fix, all that’s required is to reset the inertia switch.

Engine Sputtering and Jerking

Another common symptom of a bad fuel pump is a sputtering or jerking engine. These symptoms arise when the pump isn’t able to provide a continuous flow of fuel to the engine. It can occur if there’s a drop in pressure or with a periodic interruption in the flow of fuel. 

This can affect the combustion process and cause the engine to sputter and lead to jerky power delivery. More often than not, this symptom is intermittent. That being said, everything mentioned above can also be symptoms of other fueling and electric issues, but usually, it’s suggestive of a bad fuel pump.

Acceleration Trouble

While you would still be able to drive with a sputtering and jerking engine, it would be far more difficult to do so with an engine facing a loss of power during acceleration. This symptom can occur not just when you try to accelerate from a standstill, but also when you do something like a rolling launch. Sometimes a loss of power on acceleration can be indicative of a MAF sensor issue, or a vacuum leak somewhere in the system. However, fuel is a much more likely culprit.

An accelerating engine needs more fuel than an engine that’s running at idle or even cruising RPMs. And if the fuel pump can’t fulfill the additional demand, it’s a sign that it’s not healthy.

Loss of Power

There are times when your fuel pump will be able to meet the demand acceleration requires, but can’t supply the needed fuel under heavier load situations. One such situation is when a car is carrying or pulling a heavy load. 

Similarly, an engine also needs a strong supply of fuel when going uphill, and if the pump fails to meet the need it’s a clear indicator that it’s on its way out.

Surging Speed

While a loss of power is a more common symptom, a bad fuel pump could also give rise to surging speed. For instance, if you are driving at a specific speed and notice the car increasing the pace by itself, it’s a symptom of a bad fuel pump. A surge in the speed develops when a bad fuel pump is delivering irregular resistance within the engine and at times works harder than it is supposed to.

Engine Stalling or Not Starting

As most of the symptoms mentioned above, a stalling engine or one that’s not starting isn’t specifically indicative of a bad fuel pump. You could potentially be looking at an ignition coil failure, or something to do with spark. That being said, a fuel pump that has reached the end of its life won’t even have the juice required to keep the engine running. This can lead to an engine that suddenly stalls. A completely worn-out fuel pump also won’t be able to supply enough fuel for an engine to turn over. 

What Causes Fuel Pump Failure? 

The biggest reasons for a fuel pump to go bad are contamination, overheating, and wear. It’s quite common for debris and dirt to make their way into a fuel tank, which can then get through the filter and into the fuel pump. These contaminants end up blocking the flow and puts an unwarranted load on the fuel pump. As a result, the fuel pump works harder than it was designed to, it overheats and eventually goes bad. 

A faulty oxygen sensor is another cause of early fuel pump failure. If the sensor is reading incorrect oxygen levels, more fuel than necessary will be required by the end. To meet this uncalled-for demand the fuel pump will work harder than it’s designed to. The added stress this brings will cause the fuel pump to go bad prematurely. This is why one must make sure not to avoid any oxygen sensor warnings.

A typical electric fuel pump is made up of approximately 200 components. After many years of use, these parts can wear out causing the fuel pump to fail.

Can You Drive With a Failing Fuel Pump? 

As discussed above, most symptoms of a bad fuel pump lead to serious drivability or performance problems. If your fuel pump completely failed at the wrong time, like while on the highway, you’ll be left stranded on the side of the road. 

Less dramatic symptoms like sputtering, jerking, and surging could also prove to be equally dangerous if they occurred at the wrong time. As a result, we do not recommend driving with a failing fuel pump.

Is Fuel Pump Replacement Difficult? 

Every car is different, and the difficulty of the fuel pump replacement process varies between models. Some have it at an easily accessible location – like under the rear seat. Others, meanwhile, require the fuel tanks to be dropped. Removing the fuel tank, in many cars, can be a time-consuming and costly affair as it requires the removal of rear suspension components. 

This is also why it’s recommended to take your car to a workshop. Even experienced mechanics will take a few hours to get this done, which is why you should go in expecting it to be an expensive service.

Save Money Where You Can!

Labor costs for a fuel pump replacement aren’t going to be cheap. So make sure to get the best deal you can on a replacement fuel pump and worry not as you can do so right here! We at Newparts.com offer a wide range of OEM parts for almost all European vehicles. Head over to our Shop and find a quality OEM fuel pump to make sure your car’s engine is getting the fuel it needs.