What is a Fuel Pump?
Carbureted engines often use low-pressure mechanical pumps that are mounted outside the fuel tank, whereas fuel injected engines often use electric fuel pumps that are mounted inside the fuel tank (and some fuel-injected engines have two fuel pumps: one low pressure/high volume supply pump in the tank and one high pressure/low volume pump on or near the engine).
Fuel pressure needs to be within certain specifications for the engine to run correctly. If the fuel pressure is too high, the engine will run rough and rich, not combusting all of the fuel being pumped making the engine inefficient and a pollutant. If the pressure is too low, the engine may run lean, misfire, or stall.
A fuel pump is not necessarily required for the engine to function. The low-pressure fuel needed by a carbureted engine can be supplied simply by mounting the tank higher than the carburetor and allowing fuel to feed with gravity. This method is commonly used in carbureted motorcycles, where the tank is usually directly above the engine, and high-wing aircraft with fuel tanks in the wings.
Types of Fuel Pump
Fuel pumps come in two types: mechanical and electric.
1. Mechanical fuel pumps
Mechanical pumps are more common in older vehicles. These are driven by the camshaft or by a shaft attached to the crankshaft, which opens a diaphragm to create suction and draw fuel in through a one-way valve.
Mechanical fuel pumps are usually located near the carburetor and engine. Leading mechanical fuel pump providers include Bell & Gossett, Airtex, and Carter Fuel Systems.
How a mechanical pump works?
In a mechanical pump, the actuating lever moves up and down constantly but pulls the diaphragm down only as needed to refill the pump chamber. The return spring pushes the diaphragm up to deliver petrol to the carburetor.
The other end of the lever, which is linked loosely to a rubber diaphragm forming the floor of a chamber in the pump, goes down and pulls the diaphragm with it. When the lever pulls the diaphragm down, it creates suction that draws fuel along the fuel pipe into the pump through a one-way valve.
As the revolving cam turns further, so that it no longer presses on the lever, the lever is moved back by a return spring, relaxing its pull on the diaphragm. The loosely linked lever does not push the diaphragm up, but there is a return spring that pushes against it.
The diaphragm can move up only by expelling petrol from the chamber. The petrol cannot go back through the first one-way valve, so it goes out through another one leading to the carburetor. The carburetor admits petrol only as it needs it, through the needle valve in its float chamber
2. Electric fuel pumps
Most newer cars have electric fuel pumps. Electric fuel pumps became popular after cars began using electronic fuel injection, which works more efficiently at higher pressures than standard mechanical pumps can generate.
Electric pumps work similarly in principle to mechanical ones, but instead of using a shaft to open and close the diaphragm, electric pumps use an electromagnetic switch called a solenoid. Electric fuel pumps are usually located inside fuel tanks, although they may be mounted outside them. The leading electric fuel pump supplier is Carquest.
How does an electric pump work?
An electric pump has a similar diaphragm mechanism; it is worked by a rod that is drawn into a solenoid switch until it opens a set of contacts to turn off the current.
An electric pump has a similar diaphragm-and-valve arrangement, but instead of the camshaft, a solenoid (an electromagnetic switch) provides the pull on the diaphragm. The solenoid attracts an iron rod that pulls the diaphragm down, drawing petrol into the chamber.
At the end of its travel, the iron rod forces apart a set of contacts, breaking the current to the electromagnet and relaxing the pull on the diaphragm. When the diaphragm return spring raises the diaphragm, it also pulls the rod away from the contacts; they then close so that the solenoid pulls the rod and diaphragm down again.
How long should my fuel pump last?
Most fuel pumps last at least 100,000 miles with proper maintenance, fuel pumps can last more than 250,000 miles up to the lifetime of your car.
What can I do to keep my fuel pump in good condition?
Keeping your gas tank at least one-quarter full at all times will help extend the life of your fuel pump. Letting your gas run too low on a frequent basis will shorten the life of your pump. Fuel acts as a coolant for your fuel pump, and when your gas tank runs too low, your pump is subject to overheating.
The weight of fuel also helps add pressure to push liquid through your pump, and without this pressure, your pump has to work harder, shortening its lifespan.
Changing your fuel filter regularly every 10,000 to 15,000 miles can also extend the life of your pump. Impurities and debris from gas, dust, and dirt can accumulate on the bottom of your gas tank, and if they get sucked into your pump, they can damage it.
Your filter protects your pump, so it’s important to change it regularly. So, you’ll want to read up on how to change your fuel filter.
Make sure your gas cap maintains a good seal. A poor seal can allow fuel vapor to escape as well as allow impurities and debris to get in your tank. You should also avoid refueling at gas stations that are not well-maintained. Water in gas or corrosion on pump nozzles can get into your fuel system and damage your fuel pump.
How often should I replace my fuel pump?
Normally, you should not need to replace your fuel pump before it starts showing symptoms of wear. However, if you’ve been using your pump for more than 100,000 miles and if you’re taking your car in any way for another type of maintenance that involves removing your gas tank, it may be efficient to replace your pump during the same service trip.
8 Symptoms of Bad Fuel Pump
1. Car Experiences Hiccups
Cars need fuel to drive, just as we humans need food. It is easy to understand how important fuel is, and it is also easy to see that your car will not meet your expectations if the correct fuel supply is not guaranteed.
If you press the accelerator and feel that your car has hiccups, you may have problems with the fuel pump.
The fuel pump may be choking due to inferior fuel, or the fuel pump may not be generating enough pressure to push the fuel forward into the system.
An insufficient supply of fuel to the combustion chamber will not create enough chamber excitement to cause an explosion. No combustion means that the engine will not start at all. Even if it does, you will find that it takes you a long time to reach ignition.
If you experience that your car has misfires or sounds like a tractor at idle, you might have low fuel pressure due to the fuel pump.
3. Sudden Engine Shutdown or no starting condition
The engine needs fuel to run, and if the fuel pump is bad, the engine won’t get any fuel. If your engine doesn’t start at all or having sudden engine shutdowns while driving, there might be a problem with the fuel pump.
If this occurs regularly, it is time to arrange a meeting with your local mechanic.
Since a bad fuel pump can give an intermittent amount of fuel to the engine, you can experience misfires because of the too low fuel amount.
The engine can also get too much fuel, resulting in unburned fuel in the exhaust pipe, which will cause backfires from the exhaust pipe.
5. Check Engine Light Illuminates
Fortunately, modern cars are loaded with sensors that can detect any number of problems as soon as they occur. One of these sensors is a fuel pressure sensor that is intelligently measuring the fuel pressure. If an irregularity is detected, the sensor sends a signal to the ECU, which lights up the check engine light.
6. Thick Black or White Smoke from Exhaust
Vehicles do not normally emit black smoke from their exhaust unless they are powered by diesel fuel. If your gasoline-powered car emits such smoke, there is usually engine damage.
One of the causes of black or white smoke is a defective fuel pump, making your engine get a rich fuel mixture. In most cases, a bad fuel pump is giving a lean mixture, so this is not a very common one.
7. Turbocharger Underperforms
Turbos need time to spool air; this time is usually called turbo lag. So if you feel that there is a lot of turbo lag, your fuel pump could be a problem.
8. Spark Plugs Will Die Sooner
Fuel does actually cool down internal engine parts. With a too lean air-fuel mixture, you can actually make your spark plugs getting too hot. A defective fuel pump interferes with the internal workings of the engine.
The smallest damage occurs in the cylinder itself, and the smallest components take the greatest damage. This means the spark plugs may die before their time.
So, if you feel that your spark plugs need to be replaced too soon, you may be dealing with a faulty fuel pump.
How to fix those fuel pump problems.
So, your car’s been experiencing bad fuel pump symptoms. Sounds like an expensive, time-consuming fix, right? A fuel pump replacement doesn’t have to be either of those things. With some care and attention to detail, anyone with fair mechanical proficiency and a set of hand tools can get the job done.
As with any project, be sure you have on hand all of the parts (be sure they’re the correct parts!) and tools you’ll need for the whole job. That goes double if the car you’ll be working on is your main form of transportation. If you get the tank out and realize you need another tool, you’ll be left looking for a ride.
Before you get started replacing the pump, be sure to check your tank for any leaks or other damage since you’ll have the tank out anyway, it’ll be easy to replace the damaged fuel tank at the same time. Also, check to see if your tank has a drain cock or drain plug on the bottom side of the tank. If it does, it’ll be easier to get the fuel inside the tank out.
As with most repairs or replacements on an automobile, the cost to replace a fuel pump is less if you do it yourself. So, take your time, be patient, and be alert, and everything should go smoothly.
Fuel Pump Replacement Cost
The actual cost of replacing a fuel pump depends on several factors. The parts cost of a fuel pump is usually between $75 and $250, depending on the vehicle. If you are replacing the fuel pump yourself, beyond this it is just the cost of your time. Generally speaking, replacing a fuel pump is considered an intermediate-level task.
If you decide to go with a professional, you may be looking at a cost of between $400 and $600 to replace a bad fuel pump. You can search through our Preferred Shops in your area for a mechanic that can help with the fuel pump repair. Expect the actual replacement to take between 1 to 6 hours, depending on the expertise of the mechanic and the tools they happen to have on hand.
Whether you do the job yourself or have a professional do it, make sure that the fuel tank is properly cleaned of all contaminants, as years of fuel sediment can build up in the bottom of the fuel tank.