Why is the Fuel Pump Not Priming? (8 Causes with Fixes)

Ever been in a situation where your car cranks longer than it should? The time between the key turn and the engine thud seems to be forever. While it may seem frustrating, there is a deeper underlying issue for the long crank. 

It often has to do with the fuel pump priming. This article explains exactly why your fuel pump not priming and the possible fixes. So hang tight and read along. 

Why Fuel Pump Not Priming?

There is a space between the fuel pump and the ICE, which is known as the fuel relay of the car. Without fuel priming, the fuel replay develops a void, resulting in ICE issues. 

The main reason behind the fuel pump won’t prime may be a faulty fuel pump, the relay itself, or the internal suction mechanism that creates the air void. 

Whatever it is, it ends up creating erratic behaviour on the car where you’ll see a performance drop or failed crank every time altogether. 

For ease of navigation, we will explore that what causes the fuel pump not to prime. Now let’s get started. 

1. Faulty Fuel Pump

Before we get into the details, you need to understand three important fuel pump components–the impeller, the outlet, and the inlet plates. These two plates are part of the impeller. 

The main task of these plates is to create a sufficient vacuum on the fuel relay to drag fuel from the injector or the fuel line. 

But a fuel pump is a machine, after all. And just like any mechanical component, it can go through wear and tear in its life cycle. 

Using a fuel pump beyond its limit may often compromise the impeller outlet and inlets. 

The inability to create a sufficient vacuum may cause a low fuel pressure on the relay. As a result, you will notice that the fuel pump won’t prime. 

The obvious solution is to replace the fuel pump or work on the impeller. In any case, it would require professional intervention, so make sure to take your car to a known garage of the dealership.

Read Also: How Does A Car Act When The Fuel Pump Is Going Out?

2. Faulty Pump Relay 

The second probable cause of failed fuel pump priming is the fuel relay itself. The relay is the conduction point between the main fuel supply line and the ICE. 

When you turn the ignition key, you will hear a clicking sound after a few seconds, indicating that the fuel line has been disengaged with fuel flow. 

But a faulty fuel line will not click in place nor complete the fuel relay to the ICE. As a result, you are stuck in a perpetual ignition motion without actual ignition. 

There are two probable causes for the fuel relay failure – either general wear and tear or a loosened fuel line connection with the main fuel supply. 

The probable solution is to get the fuel relay replaced altogether. But if you notice that the connection is loose during an inspection, just reposition the fuel relay with the fuel supply. You will still need to take the car to the dealership or garage for inspection. 

3. Faulty Battery

The fuel pump is operated electrically. Regardless of whether you go with a self-priming or manual priming fuel pump, the pump is started using the car’s battery. 

Now, if you have a failing battery or a battery that can’t push power to the pump, the pump will fail to start up and create the necessary vacuum needed to initiate the priming. 

The tell-tale sign of battery failure is the complete failure to start the car. You will see that the car will only make ignition noises, but even after 10 or 20 seconds, the car won’t start. 

The only possible solution in this regard is to get the battery replaced.

Read Also: What To Do If Fuel Pump Making Noise But Not Pumping Fuel?

4. Suction Line Leak

The impeller with the outlet and the inlet ports creates a vacuum on the suction line. This vacuum creates the necessary pull of fuel from the main fuel supply line. 

We have already mentioned that the outlet and the inlet or the impeller failure may cause the vacuum not to develop. 

However, if there is a leak in the suction line, the vacuum won’t hold, resulting in a failed fuel supply. The obvious sign of a suction line leak is the erratic idling of the car. 

You will see the car constantly showing low fuel pressure or coming to a stop altogether. The only solution to this problem is to replace the suction line. 

5. Faulty Fuel Pump Fuse

We examined how the failing battery will fail to provide the necessary power to the fuel pump. The same problem will happen if the fuel pump fuse fails. 

In the case of a fuel pump fuse failure, the battery will not be able to send the power to the fuel pump resulting in a failed priming situation. The only solution in this regard is to replace the fuel pump fuse.

Read Also: 12 Weak Mechanical Fuel Pump Symptoms You Should Know

6. Faulty Check Valve

The check valve is used to monitor the level of fuel pressure on the fuel supply line. This is where the fuel is supplied to the suction line and fuel relay. 

If the check valve is faulty, there won’t be sufficient fuel pressure to supply. The result is again the failure of fuel pump priming and supply of fuel to the ICE. 

7. Faulty ECM

The ECM sends a pulse to the ground or deactivates the fuel relay, which clicks in position to start the priming position. But a faulty ECM will fail to send the pulse to the relay, and it will not get grounded. 

You may look at the fuel relay and find no apparent problem, unless you’re looking specifically for the ECM issue. The solution here is to get the ECM replaced. 

8. Debris in Fuel Tank and Injector

A bad fuel or debris in the injector may also cause the fuel pump to not prime. Bad fuel may hinder the filter system in the fuel line and result in a short supply of fuel to the suction line. 

The same problem may occur with debris in the fuel injector, and the line will fail to supply proper fuel to the relay. 

The solution here is to clean the tank, fuel filter as well as injector. As a pro tip, always use good quality fuel.

Read Also: 7 Symptoms of a Defective Fuel Pump Driver Module

What’s The Cost of Fixing If your Fuel Pump Not Priming?

The cost of fixing a fuel pump that is not priming can vary depending on a number of factors, including the make and model of your vehicle, the location of the fuel pump, and the labor rates of the mechanic you choose. However, you can expect to pay between $150 and $400 to have a fuel pump replaced.

Frequently Asked Questions

Now that you know everything there is about the fuel pump not priming, let’s look at some of the common questions that the users are asking.