Knowing some of the causes of a fuel pump problem may come in handy.
It can enable you to solve the fuel pump problem or at least give a good estimate of what lays ahead of you in terms of repair and cost.
Even if you can’t solve the problem on your own and you have to seek professional help, some pre-existent knowledge may save you from unwanted or unneeded expenses.
If you want to see what are some of the common symptoms of a bad fuel pump, click here for a separate article on that topic.
MOST COMMON CAUSES OF A FUEL PUMP PROBLEM
1. FUEL PUMP
A fuel pump is a mechanism that is in charge of pumping fuel from the gas tank to the engine.
It’s a direct current electric motor connected to an impeller in one housing. Once it’s given electric input, the motor turns the impeller and it starts pushing fuel.
This is an explanation in a nutshell. If you want to learn more about the fuel pump, click here for a great explanation on Wikipedia.
Common causes of a fuel pump failure is either the motor armature (parts of the electric motor like the rotor, brushes, or else) and the impeller which pushes the fuel into the system.
The most common reason that leads to this, by far, is driving on a low gas level all the time. You see, the construction of the fuel pump is such that it uses fuel to cool it down.
Direct current motors are prone to heating up and since it works all the time the fuel is used as a sort of coolant.
If the fuel level is low, the fuel pump will constantly overheat which will eventually lead to failure.
Anyway, almost all fuel pumps are built in such a way that they can’t be opened and successfully repaired. This is done mostly because the pump is constantly in contact with fuel so it has to be tightly sealed.
Most fuel pump housings are crimped so opening them is essentially a one-way trip. You can open them but can’t successfully return everything into place.
There are fuel pumps that can be dismantled (especially ones mounted outside the gas tank) but this is rare and present mostly in older car models.
So, complete replacement is the most common solution here.
Another important thing to know is that there are essentially two types of fuel pumps:
External ones, located outside the gas tank (on the tank itself or on the engine, in case of older, mechanical type pumps)
External pumps are made to be replaced separately while the fuel gauge sender stays intact.
Fuel pumps located inside the gas tank; these are usually combined with the fuel gauge sender in the same housing. Very common in most modern cars (this type is in the picture above).
In this case, the fuel pump is usually replaced together with the fuel gauge sender as it is one part, in one plastic housing.
Sometimes the fuel pump can be replaced separately (taken out of the housing) so the fuel sender gauge can be saved.
In the majority of cases, replacing the whole part is the best and sometimes only solution.
2. ELECTRIC CONNECTION
When the fuel pump is working properly, you’ll hear a characteristic buzz sound coming from the gas tank when you turn the ignition key to the first position.
If the sound doesn’t appear this may mean that there’s no electric input to the motor.
Then, the electric connection on the fuel pump is the first place to check.
Best first take a tester and check out whether or not there is an impulse coming from the electric installation.
The main hotspots for this kind of a fuel pump problem is the electric connector and the wiring installation.
Externally mounted pumps (outside of the gas tank) are especially prone to these problems.
In this case, the pump is more subjected to outside elements like filth, moist, or physical damage (although the contacts have rubber or plastic protective caps).
Moist and filth lead to rust which then leads to a lack of contact and eventually, the fuel pump can stop working. In case of severe rust, the contacts may even break off.
The wires that lead to the fuel pump should also be checked for eventual damage especially at parts where they are exposed or bent.
In the case of a fuel pump combined with the fuel gauge sender in one housing, the contacts are usually located on top of the housing.
Bad electric connections are more rarely the problem with this type of pump as the housing is in a pretty protected location (on top of the gas tank with access from the passenger cabin or boot).
Besides this, the connectors usually have rubber caps on them for additional protection.
Rust appears mostly if there is a moist present.
A more common fault, in this case, maybe a damaged wire (mostly due to lack of space as well as the hatch lid pinching a wire).
3. FUEL PUMP FUSE
If the connections are OK and there is still no electric input to the fuel pump, the fuse box is the next place to check.
The fuse usually burns out if there is a short circuit in the electric system (like a damaged or pinched wire, damaged connector or else) or because of an electric overload (like if the fuel pump motor is at the end of its service life and stalls, overheats or totally jams).
A burnt fuse is also the easiest fuel pump problem to fix.
This may be a temporary fault in which case the fuse is simply replaced.
If the fuse continues to burn out, then there’s a more serious problem and should be inspected as soon as possible.
If you’re interested in how to replace a car fuse, click here for a separate article on that topic.
4. FUEL PUMP RELAY
If the fuse is OK, but there is still no electric input to the fuel pump, the relay is next in line to check.
The fuel pump constantly uses a significant amount of electric power and this is why the relay is installed.
The main cause of problems is material fatigue (the contacts inside the relay burn out over time).
Another common problem may be the contacts for the relay in the contact board.
A pretty simple repair under the circumstance that you can exactly locate the fuel pump relay and that you’ve determined that the relay is the actual problem.
5. FUEL PUMP FILTER
To make things clear: besides the main fuel filter located on the fuel line, there is on more filter located just before the fuel enters the fuel pump.
This problem is present mainly with fuel pumps that are combined with the fuel gauge sender.
The filter is located at the bottom of the housing and looks like a sock.
It can get clogged due to debris deposits that form over time on the bottom of the gas tank.
This filter is often overseen as a problem (especially in a DIY repair option) as a lot of people are not aware of this other filters existence.
One more thing on this part: externally mounted fuel pumps may also have small fuel filters inside them.
Sometimes these filters can be cleaned if the housing type allows proper dismantling.
This is a more rare option and is mostly present on older type fuel pumps.
6. FUEL LINE CONNECTIONS
Another checking point in the case of a fuel pump problem is the fuel line connection to the pump itself.
The most common problem is either a damaged fuel hose, connector, or a loose, faulty clamp.
Damaged hoses are pretty common as fuel is an aggressive substance that can over time cause the hoses to become brittle and break.
Most of the damage happens at the weakened parts where the hose slides on the plastic or metal intake part of the pump.
Sometimes the hoses are held in place by plastic connectors (clip-on system). These are pretty resilient but can give in if the hoses are taken off several times.
Loose or damaged clamps may appear if some previous work has been done (like replacing the gas tank for instance). It happens as an oversee or if in some previous time the clamp has been overtightened and damaged.
7. FUEL PUMP SEAL
This problem appears with fuel pumps that are combined with the fuel gauge sender.
A thick rubber gasket is located between the fuel pump housing and the gas tank ledge (in most cases).
Its main task is to seal the connection between the fuel pump housing and the gas tank.
This fault is pretty rare as the gasket is pretty resistant. Nevertheless, it’s worth the check.
If it does happen, material fatigue is the main cause. The rubber may become brittle and lose the ability to seal properly.
This leads to air getting into the tank. If it does, the pump cant achieve proper pressure.
It will also be accompanied by a strong smell of fuel inside the passenger cabin.
8. ECU UNIT
The ECU unit, or the car’s computer, is in command of almost all the cars vital functions.
Such is the case with the fuel pump, namely it’s power supply.
When the ECU is faulty, there will be no power supply to the pump or the relay.
This is a more rare fault but if everything else checks out OK regarding the power supply, it’s worth taking a look.
On this part, I would avoid a DIY option and seek professional help, mainly in terms of proper diagnostics, repair, or replacement.
The proper tools and expertise are necessary to finish the job, otherwise, you may just get yourself into trouble.
A fuel pump problem should be solved as soon as possible.
A bad fuel intake will cause the engine to function improperly which can damage it over time.
Also, it can endanger the driving safety as the car will sputter, surge, stall, or even completely cut out.
Hopefully, some of these causes will lead to some sort of solution.
If you decide for a DIY option proceed with some extra caution as your dealing with highly flammable fuel. Make the necessary safety precautions before starting.
One more thing, make sure that the fuel pump is the actual problem. Some symptoms are similar to other car problems.
This goes does double for cars where the gas tank has to be taken off completely.
In these cases, it has to be done in order to reach and replace the fuel pump.
The last thing you would want to do is go through all that work and conclude that the fuel pump isn’t the actual problem.
Written by: Sibin Spasojevic
Former car technician, life-long car and DIY enthusiast, author for Despairrepair.com