How to check for a bad fuel pump

My name is Vince and in my years of owning different vehicles, I only dealt with a single bad fuel pump. However, the other day my brother-in-law calls me up and says,

“Yo Vince, my Jeep Cherokee is making this whining noise, has a hard time starting, and sputters when I’m driving down the road.”

I knew right off the bat that he had some fuel issues. So I brought my handy scan tool over, and pulled a P0231 Diagnostic Code. Yup, we replaced that part and bam, the ‘ol Jeep started purring like a kitten again!

bad fuel pump

What is it?

The fuel pump is exactly as it sounds. It pumps the fuel from the tank into the fuel lines and injectors to begin the combustion process. In all honesty, the fuel pump is designed to last the life of the vehicle.

But what happens when the fuel pump goes bad? What are the symptoms? Is it easy to fix? I’ll answer all those questions along with the steps on how to check for a fuel pump malfunction.

Why does a fuel pump fail?

The electrical fuel pump is a complicated yet durable device. A complete fuel pump assembly in a modern car may or may not include a pressure sensor, a pump intake strainer (internal fuel filter), a pressure regulator valve, a fuel gauge sending unit, and the actual electric pump.

Now, the fuel pump itself consists of two main parts:

  1. The pump
  2. Brush-type DC motor.

When it fails, it’s mostly blamed on the brushes in the motor. As it operates (or as the brushes touch the rotating copper contacts), it generates a lot of heat. If the heat is not vented from the brush-type motor, it may overheat and create burnt particles of carbon in the copper contacts.

So how does the fuel pump keep cool?

There’s a reason why modern fuel pumps are designed to be submerged inside the tank. The gasoline in the tank is responsible for cooling the fuel pump! You may find this hard to believe, but it’s true. As the fuel is siphoned through the pump, the heat from the motor is also carried away from the unit itself.

A typical fuel pump runs at 100 degrees Fahrenheit on a cold day. If the fuel is near empty, there won’t be enough fuel to absorb the heat from the pump. So if you have a habit of driving with consistently low fuel levels, you run the risk of damaging or deteriorating the performance of this part.

And if the brushes deteriorate further (or if the carbon build up gets thick enough), it increases the electrical resistance of the fuel pump, which also leads to a reduction in power of the electrical motor. If the motor gets too weak to run, then your vehicle won’t start.

What happens when the fuel pump goes bad?

You won’t be able to drive your car! Or you’ll get stranded in an empty and desolate parking lot far away from home! In either case, it looks bad. But the fuel pump won’t fail instantly. There are symptoms you need to watch out for. If you’re lucky, you can diagnose this trouble before it completely fails.

5 common symptoms of a bad fuel pump

Here are the symptoms of a malfunctioning fuel pump:

1. Check engine light in the console

This means the ECU is grabbing hold of OBD2 trouble code/s. The only way to find out the trouble code is to connect a scan tool in the OBD2 port. The trouble codes associated with a bad fuel pump are P0201, P0267, P0268, P0231, P0232, P0030, and P0087. Keep in mind the trouble codes will also depend on the make and model of your vehicle.

2. Poor or unstable idling

A defective fuel pump will have trouble supplying the right amount of fuel in any given situation, even during idling.

3. Engine stalling

This is one of the most common symptoms I look for. In some cases, the engine runs fine but will stall after a few miles of driving. The vehicle will restart but will stall again immediately or after a couple of minutes. If you’re familiar with this situation, it’s time to have the fuel pump checked immediately.

4. Poor engine performance

If the engine feels low in power, this indicates a drop in fuel pressure. When this happens, the engine is basically starving for fuel, which leads to poor acceleration, hesitation, jerking, and surging.

5. The engine refuses to start

If the pump fails completely, you’ll have a no-start condition. When this happens, the engine is not completely dead. If you turn the key, you’ll still hear the engine cranking, but it won’t start.

How to check for a failing pump

Here are the steps on how to check for a malfunctioning one –

1. Start with the Check Engine Light (CEL)

Is there a check engine light? Is the car running or does the engine refuse to start? If you have an illuminated check engine light, you’ll need a scan tool to read the trouble codes. For all you know, the problem might be caused by other problems besides the fuel pump. If you’re not sure how to do this, don’t hesitate to consult a professional mechanic.

But in some cases, the fuel pump may fail without a check engine light. If this is the case, proceed to the next step.

2. Is the fuel pump is clicking or whining?

The fuel pump will make a faint whining or clicking noise when running properly. But if it’s beginning to fail, it will make a much louder and annoying whining noise.

Turn the key to the ON position and listen to the sound near the rear of the vehicle (close to the gas tank). Have a friend or help out. Let them turn the key so you can listen to the fuel pump. If you hear only a faint clicking or whining noise, you’re likely OK.

But if you don’t hear anything when you turn the key, proceed to the next step.

3. Relay and fuse

This is relatively easy to do. The relay supplies the current flow to the fuel pump. It also pressurizes the fuel lines by supplying the fuel pump with electricity before starting the vehicle.

Open the hood and locate the fuel pump relay in the large fuse box. Check for the main fuse as well. The fuse is easy to check, but how about the relay? I have a separate article on how to check the fuel pump relay using a multimeter. But if you don’t have a multimeter, the relay should emit a faint clicking sound as you turn the key as well.

If you’re lucky, the relay might be the cause of why the pump is malfunctioning!

But if the relay and the fuses are fine, proceed to the next step.

4. Proper fuel pressure

There are many ways to do this, but the proper way is to use a $20 fuel pressure gauge. In most cars, there’s a fuel test pressure port under the hood. Simply hook up the fuel pressure gauge and turn the key to crank the motor. If the gauge is reading zero, it means there’s no fuel pressure. If the engine is still starting, rev the motor and watch the fuel pressure rise. If it doesn’t rise or if the readings are off, proceed to the next step.

5. Fuel filter

If your vehicle has a serviceable fuel filter, replace it first before removing the fuel pump. A clogged or dirty fuel filter will restrict the flow of fuel, which leads to a drop in fuel pressure.

But in most modern cars, the fuel filter is part of the fuel pump assembly and is also located inside the tank. The reasoning here is if you need to replace the filter, it’s also time to replace the fuel pump.

Step 6: If there’s nothing wrong with the fuel filter, fuse, and fuel pump relay, it’s time to replace the fuel pump.

In some cars, the fuel pump can be accessed from inside the rear passenger compartment or in the trunk. But in some cars, you’ll need to remove the rear sub-assembly to remove the tank and gain access to the pump.

If your car belongs to the latter, it’s better to take it to a mechanic rather than doing it yourself. Removing an entire sub-frame demands expert skills and a complete set of tools. This is the problem with most cars.

This is a Labor intense job and the cost for this type of job can easily reach $1,000. If you do it yourself, the part itself is only around $100.

How can I protect from early failure?

There’s not much you can do to protect or preserve the integrity of the fuel pump. However, there are some basic things to consider if you it to last 200,000 miles or more.

It all begins by erasing the habit of driving with a near empty tank. Since the fuel pump relies on the fuel for cooling and lubrication, make it a habit to consistently maintain a full or half-full tank at all times! The lowest you can go is one-fourth tank, and even then the fuel pump might still overheat or run too hot especially in the summer.

You should also consider the quality of the fuel inside the tank. Using cheap and low-quality fuel may introduce dirt, rust, or water in the fuel tank.

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