Car Won’t Start After Replacing Fuel Filter? 10 Causes And Solutions To Fix It!

Car Won't start after replacing fuel filter
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The fuel system components of the vehicle like fuel filter, fuel pump, fuel pump strainer, fuel injectors, fuel pressure sensor, pump fuse, fuel pump relay, etc. play an essential role in the operation of the vehicle.

We all know that out of the several components, the fuel filter is one of the important maintenance items when it comes to ensuring the proper functioning of the vehicle.

Since the fuel system delivery line is always kept under pressure to ensure the lifting of the fuel from the fuel tank to the engine, we need to follow certain procedures and precautions while dismantling and replacing the fuel filter of your vehicle.

The issue of car won’t start after replacing fuel filter is mainly due to an air trap in the fuel system resulting from improper priming of the fuel filter. So you need to ensure a steady stream of fuel flow at different locations and no air trap in the fuel system circuit to fix the hard starting problem.

If you are also facing the issue of the car won’t start after replacing fuel filter, then you are at the right place! Here in this article, we will cover everything you need to know. Stay tuned!

How To Prime a Diesel Fuel Filter?

The fuel filter plays a key role in filtering the fuel and ensuring clean fuel to the engine for combustion.

The foreign matters in the fuel need to be filtered, otherwise, if it finds its way to the engine, it may clog the injectors and would lead to starting problems and the car won’t start after a while.

The fuel filter has some limited dust carrying capacity up to which it will perform the function of filtering the fuel effectively without affecting the performance of the vehicle.

Once the fuel filter reaches its filtering limit, it reduces the pressure of the fuel across the filter element resulting in reduced fuel flow rate, pressure, and the hard starting problems associated with it.

Hence it is essential to replace the fuel filter as per guidelines given in the owner’s manual.

There is a certain procedure that needs to be followed while replacing the fuel filter to prime a diesel fuel filter to ensure trouble-free vehicle starting and running. Below are the steps to prime a diesel fuel filter.

Fuel filter installation requirements

First of all, remove the battery negative terminal while working with the fuel system as a safety precaution and it is also better to have a fire extinguisher nearby.

Loosen the screw or plastic nut on the top plate of the fuel filter and remove the top cap.

Remove the old fuel filter element from the canister and replace it with a new filter element.

In some cases, you may need to remove the entire fuel filter canister with an inbuilt filter element and replace it with a new fuel filter assembly.

Of course! you can retain the old water separator assembly after replacing new fuel filter canister.

In a few vehicles, the new fuel filter element has to be rotated either clockwise or anticlockwise to remove and assemble it to the filter canister or filter mounting body. The design varies between different vehicle manufacturers.

Remove the O-ring or seal from the fuel filter top cap and replace it with a new sealing gasket. Ensure that it is not moved around and shall fit properly and lined up at its intended position, otherwise, it may start leaking fuel and air in the system.

If the fuel filter is mounted vertically, then fill the fuel filter with clean fuel till it is filled to the brim to prevent airlock in the system and assemble the fuel filter with the top cap, put it back altogether, and tighten the screws of the top cap or rotate the fuel filter canister till it fits tight.

Priming with priming bulb

Some vehicles have a priming bulb located just before the fuel filter to prime the fuel filter by pressing the bulb to take out the air that intruded in the fuel system while replacing the fuel filter.

You need to ensure a steady stream of fuel coming out at 3 locations one after another.

First at the outlet of the priming bulb and second at the engine-mounted fuel pump inlet located after the fuel filter and the last one at the inlet of the fuel injectors.

While relieving the air trap at the injectors, you may just half turn the nut at the injectors to loosen it. You may use two wrenches, one to grip the steel lines and the other for the nut to prevent bending of the steel lines.

Usually, it is sufficient to bleed just half of the lines at a time. Once the fuel comes out of the injectors, just tighten the injector nut to seal it.

You need to crank the engine to force out all air while doing the above processes to confirm no air trap in the line between the fuel filter to the engine injectors.

Priming with hand pump or plunger

Some fuel filters have a manual hand priming pump or plunger sitting on the top of the fuel filter for bleeding the air out of it to prime the fuel filter.

Loosen the bleed torx screw and press the hand pump up and down several times till the air bleeding noise dissipates and a steady flow of fuel comes out of the bleed valve without air bubbles.

Once all air is bled out, fit the bleed screws to plug the bleed valves.

Priming with ignition cycles

In the case of vehicles with an in-tank electric feed pump, after you have confirmed all the above steps, it’s time to start the vehicle ignition.

Turn the ignition key ON (do not crank the engine) for 5 seconds and turn it OFF. Repeat the process 3 or more times depending upon the amount of air trapped in the system.

This ensures that the in-tank fuel pump runs for 3 seconds and keeps the fuel delivery hose under pressurized condition on the back of the engine injectors.

This indirectly primes the fuel filter and the fuel system, thereby making it ready for atomization and combustion when you start the car.

On the fourth turn, go ahead and crank the engine, the vehicle should start. Make sure that you run the engine at least for 30 seconds before turning it off to ensure complete removal of the airlock if any.

If your vehicle has a Schrader valve in the fuel system circuit, then you may remove the fuel pipe after the valve and confirm there is no restriction in the fuel flow.

Car Won’t Start After Replacing Fuel Filter? 10 Causes And Solutions To Fix It!

People often face the issue of the car won’t start after replacing fuel filter or right after they make any other changes to the vehicle during maintenance.

A few times the issue may be related to the changes done but what if the issue is due to the failure of other parts? The coincidence of the failure of other parts can’t be ruled out. Isn’t it?

Below are the few possible reasons for the issue of the car won’t start after replacing the fuel filter.

Air trap in fuel lines

After replacing the fuel filter, the fuel lines remain empty and there are chances of air getting trapped in the fuel system circuit, hence the car won’t start.

Several steps need to be followed to prime a fuel filter as we discussed above like usage of priming bulb, hand priming pump, bleed valves and screws, filling the filter with fuel, replacing O-rings and seals, loosening injector nuts and ignition ON-OFF cycles, etc.

It is necessary to prime the fuel filter and the system to avoid hard starting problems after fuel filter change to remove the trapped air from the fuel system circuit to ensure the required delivery of the fuel to the engine.

Wrong Fuel hose connection

Have you confirmed that the fuel hose is not connected at wrong filter ports? Typically, the fuel filter allows fuel to flow freely in one particular direction.

Flow directions marks are usually provided on the fuel filter to ensure proper orientation.

Fuel hoses can accidentally be switched if you are not careful and many times filter inlet nozzle is connected by mistake to the engine, thereby affecting the fuel delivery to the engine, hence the car won’t start after the fuel filter change if it is not installed in the correct orientation!

You may check the fuel pressure at the Schrader valve or at some location downstream of the fuel filter using a fuel pressure gauge to confirm whether the fuel is even reaching the engine or not?

Improper fuel pump priming

Did you prime the fuel pump by turning the ignition ON-OFF 4- 5 times? If not, it is time to do one.

As mentioned in the fuel filter priming section, after fuel filter replacement, you need to do fuel pump priming to build enough pressure in the fuel supply line.

If the pressure gauge reading shows under pressure due to an airlock in the system, then the car won’t start after fuel filter change.

Fuel pump priming action runs the fuel pump for 3 seconds each time when you turn the ignition key on and thus pressurizes the fuel line circuit to supply fuel to the engine.

You may like to read this article: “Fuel pump primes but no pressure? Everything you need to know!

Kinked or leaky fuel hose

If you have accidentally kinked or damaged any fuel hose while replacing the fuel filter, then it would introduce a large fuel pressure drop in the fuel system circuit and thereby restrict the fuel flow and would lead to vehicle starting problems.

Also same may be the case with the leaky fuel filter. Hence you need to ensure that all the connections are leakproof.

So it is a prerequisite to inspect the entire length of the fuel supply hose starting from the fuel pump at the vehicle rear till the engine injectors end to identify any possible damage, wear, tear, and replace the fuel supply hose if required.

Bad fuel pump

If the in-tank fuel pump is not supplying fuel with adequate pressure and flow rate to the engine, then it would be the case of a failing fuel pump that has become dead from just bad condition.

The fuel pump owing to its rotary parts becomes defective after covering some mileage.

The fuel pump also gets entangled with foreign matters, if the fuel pump starts sucking unfiltered fuel directly from the fuel tank through the vapor jet port when the fuel strainer gets clogged significantly.

Car won’t start even if you change the fuel filter unless the fuel pump is replaced with a new one if the fuel pump which is a pre-requisite for the vehicle starting doesn’t supply fuel as per engine demand.

Clogged fuel strainer

We all know that the fuel pump strainer is one of the important maintenance items when it comes to the fuel pump assembly module.

The reason for the fuel filter replacement is clogging. Right? The fuel strainer clogged condition may coincide with the fuel filter clogging since the latter clogs up due to the unfiltered fuel passed on by the fuel strainer. This will either reduce the delivery pressure or block the fuel flow across it.

The placement of fuel filter or strainer is of prime importance. People often get confused whether the fuel filter to be placed before or after pump for best pump performance, but this depends on type of fuel filter, mesh size and type of fuel pump.

The in-tank fuel pump also needs to work harder and draws more current and burn out, so clogged fuel strainer is also the single most reason for a failing fuel pump.

Hence it is necessary to check the condition and replace the fuel strainer with a new one if the car won’t start after replacing fuel filter.

Bad relays

Have you checked the proper functioning of the parts which are required for starting the vehicle? This includes fuel pump, starter motor, ignition switch, etc.,

If not, then it is time to confirm once. If one of the starting systems is not operational, then check the concerned relays like the fuel pump relay, the starter relay, or the ignition relay to confirm that the parts are getting the required power supply for its operation.

The bad relays will not supply power to the vehicle starting system parts and the car won’t start even after replacing fuel filter unless the relays are replaced with a new one.

Blown up fuse

The fuel pump fuse getting blown up is one of the frequently reported issues. This may be due to a failing fuel pump drawing more current to do more work, thereby ending up blowing the fuel pump fuse which needs to be replaced.

Similar to the relays, the fuse needs to be inspected in the same line. If you are wondering why the car won’t start after fuel filter change? Then you have got one more part to diagnose.

Faulty fuel pump pressure regulator

There are three types of fuel pressure regulator (FPR), one is inbuilt FPR in the fuel pump mounted on the tank and the second one is the inline FPR located between the fuel filter and the engine and the last one is the gas rail FPR.

If the fuel pressure regulator turns faulty then it will not maintain the pressure required for the atomization of the fuel when it reaches the injector and leads to car starting problems unless the FPR is replaced with a new one.

It is quite natural to diagnose the issue at the fuel filter end since you have replaced it, but in reality, the issue may lie at some other parts of the engine.

Drained out battery

Are you working on your vehicle for a long time? If yes, have you kept the door opened by mistake while replacing the fuel filter?

Then you have all reasons to drain the battery to a level at which your car won’t start, similar to a headlamp draining the battery when you accidentally keep the headlamps ON overnight.

Jumpstart your vehicle to confirm that the car starting problem after fuel filter change is not due to battery drain since the car requires a significant amount of cranking amps at the start.

Final Thoughts

The fuel filter plays an important role in keeping the engine free from foreign particles and it also acts as a water separator.

Since it is a regular maintenance item, we replace the fuel filter at defined intervals, but many times what needs to be done after replacing the fuel filter is often not mentioned in the owner’s manual.

So some folks would report that the car won’t start after replacing fuel filter.

If the hard starting problem is only because of this replacement change performed in your vehicle, then if you honestly follow all the steps mentioned to prime a fuel filter then the vehicle starting problem would not arise after fuel filter change. 

It is obvious to doubt the fuel filter replacement activity, but what if the starting problem is related to issues in some other parts that surfaced after fuel filter change just by coincidence? Hence it is essential to investigate other problem items involved.

You may use the method of elimination to zero in on the part which leads to car starting problem.

If after using a carb. cleaner or starter fluid into the throttle body, the engine turned ON and but when the fluid ran out the car shut off, then the issue is apparently due to the inadequate or no fuel supply to the engine.

Hope we tried to collate all possible reasons for the issue of the car won’t start after replacing fuel filter and the solutions to fix it.

With these tips in hand, hope you would try to figure out the root cause of the problem and fix it!

Happy Motoring!




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