The Symptoms of a Bad Fuel Pump
If your car burns gas, then it has at least one fuel pump in the system. It’s one of the components that your engine can’t run without, even if the tank if full to the brim. It’s responsible for delivering all that precious fuel from the gas tank to the engine, and there’s absolutely no room for failure.
The cost to replace a fuel pump ranges from $200 to $1,250 or more depending on the vehicle and the fuel pump style. In most cases, it takes a couple of hours or so to change the faulty fuel pump, and the bulk of the repair cost tends to be in the part itself, especially if you need a complete fuel pump module assembly.
What does it look like when you have a bad fuel pump? Let’s explore what a fuel pump is, signs of a bad fuel pump, and what you can do to fix it.
What is a fuel pump and how does it work?
A fuel pump is a small electric motor that transfers fuel from the tank to the engine. In older vehicles, the fuel pump is mounted along the frame rail, fastened into the fuel line. Classic cars often use a mechanical fuel pump at the engine that pulls fuel to the front of the car rather than a pump at the back, pushing it forward.
Modern cars almost all have the fuel pump inside the fuel tank. The small cylindrical pump is part of a larger assembly that includes a fuel level sensor and a fuel filter screen. Generally, pumps can produce more pressure by pushing fluid through the line rather than drawing it up.
A fuel pump for today’s engines usually uses an impeller-style system that pulls fuel through it, creating positive pressure on the engine side of the pump. Other styles including a rotary vane and gerotor pump are available for select models, but they’re far less common.
Once the pump has built pressure, it’s intended to hold it by preventing fuel from bleeding back into the tank. In this way, there’s always fuel in the line, primed, so you can start your engine quickly whenever you need to.
How long does a fuel pump last?
The strict tolerances in manufacturing for fuel pumps means that they last much longer than they used to. It’s no longer uncommon for a fuel pump to last ten years or longer, and 100,000 miles is well within normal. But that’s not a guarantee since fuel pumps can fail from overheating or sitting with bad gas in them too long, or in the rare occurrence of a manufacturer’s defect. And if it goes bad, you’ll need to deal with it right away.
Signs Your Fuel Pump is Going Bad
Trying to figure out how to tell if a fuel pump is bad has a few tricks. The common signs of a bad fuel pump include:
- Whining noise coming from the fuel tank area when the engine is running.
- Stalling that will restart after several minutes.
- Trouble starting the car.
- Lack of power.
- Long cranking time.
A whining noise from the tank often is a precursor to loss of pressure or total failure. It can sometimes last with a bad fuel pump sounds for hours, weeks, or indefinitely. If the pump is whining, keep a close eye on it.
Car is Stalling
If your car is stalling and it will restart after sitting for a bit, the fuel pump may be overheating. The cause is often from being operated with low fuel in the tank frequently, since the gas actually cools the pump too. Odds are that it will completely fail soon.
Difficult to Start Your Car
Difficulty starting the car can be an indication that the pump has quit altogether or has extremely low pressure, and lack of power when you’re driving is also a symptom of bad fuel pump that goes hand in hand.
Long Cranking Time
Long cranking time usually indicates that a fuel pump won’t hold positive pressure in the fuel line with the engine off. The fuel has bled back to the tank, and cycling the key is necessary to re-prime the line before the car will fire up.
How to test your fuel pump
Testing a fuel pump can be deceiving. One of the issues is that it can cut out intermittently, or it might just be completely dead. There are a few things to check if your car won’t start or run well.
Check the fuse and fuel pump relay on the fuel pump circuit. A blown fuse or signs of a bad fuel pump relay usually indicates that the pump is drawing too much power, especially if it happens more than once.
Perform a fuel pressure test. Either purchase a fuel pressure test gauge or borrow one with AutoZone’s Loan-A-Tool program. Connect it to the fuel pump rail to test for fuel pressure, then compare it with the manufacturer’s spec. Low pressure is a clear indication that the pump needs to be replaced.
Tips for replacing your fuel pump
Each model has unique needs to replace a fuel pump although the general process may be similar. Start with disconnecting the battery as a spark near an open fuel source is never a good thing.
Since almost all fuel pumps are inside the tank, you’ll need to access the top of the tank. In some cases, that can mean lifting the vehicle and lowering the fuel tank, but some cars have access ports under the rear seat or in the trunk compartment, so always check the procedure beforehand.
Clean the dirt and debris from the top of the fuel tank before opening it, preventing loose dirt from falling into clean fuel. Disconnect and label the wires and hoses to ensure they go back in exactly the same way on the new pump.
When the repair is complete, cycle the key a few times to prime the fuel line before you crank the engine over. That will purge air from the fuel line for a faster start-up.
Your fuel pump should last for several years, and possibly even your vehicle’s whole lifespan. But if you’re experiencing problems with starting, reliability, or performance, it might be time to diagnose and replace the fuel pump.
If that’s the case, get your fuel pump replacement at AutoZone. With an excellent selection of parts from top manufacturers for virtually any year, make, and model, you’ll find exactly what you need.