A fuel filter is located in the engine compartment, or under the fuel tank in an automobile. Its primary function is to filter out the large rust particles in the unfiltered fuel. The fuel used for running the automobiles may be contaminated with dirt, paint chips, rust, etc. Hence, a fuel filter also gets clogged with these impurities over a period of time, resulting in obstruction of fuel flow.
Problems due to Clogged Fuel Filter
When the engine starts, the fuel enters the fuel filter first, before it enters the fuel injector. A fuel filter is a mesh like substance which filters out the unwanted particles from the fuel. However, this fuel filter, when clogged with impurities can give rise to following problems:
Engine Does Not Start
Engine gets its supply of fuel from the fuel injector which initiates the ignition. However, if the fuel filter is not functional, the fuel does not flow steadily into the vehicle's engine. This causes engine hesitation or engine stumbling, even when the vehicle is accelerated repeatedly from a stop. If the filter is completely clogged, it does not allow the fuel to flow through and hence the vehicle does not start at all. This is a common problem with older vehicles that contain carburetors.
In case of a clogged fuel filter, due to an interrupted flow of fuel, the engine may function erratically. This condition is also termed as rough engine idle. A damaged fuel filter can lead to negative engine performance, causing deviation from the appropriate fuel-air mixture. Many times, if your engine suddenly stops without a rhyme or reason, first check for the fuel filter.
Low Speed and High Speed
It is evident that if the fuel filter is plugged totally with impurities, other aspects of engine (like speed) is bound to get affected. One might have observed that in such a case, there is a credible difference in the fuel flow pressure between high and low speeds of engine. During high speed of the engine, the pressure to pump the fuel is more. Hence the fuel somehow passes through the fuel filter and a normal engine operation is resumed. But if the engine is operating at low speed, the pressure required to pump the fuel through the contaminated filter is not enough, thereby resulting in a poor engine performance.
Start and Stop
This is a very common problem encountered by many of us, when driving vehicles with a clogged fuel filter. Although the fuel flow is obstructed intermittently, the fuel flows through the filter when the engine is accelerated. And then suddenly, the next moment, the engine comes to a halt. This problem is known as the start and stop problem, where the fuel flow alternates between flowing adequately and getting restricted through the fuel filter.
Detecting Fuel Filter Problems
One can carry out fuel pressure and volume test to affirm the possibility of a bad fuel filter. In a fuel pressure test, the pressure regulator is checked thoroughly to see if there is any change in line pressure in response to the changes in the engine vacuum. If any anomaly is detected, first check the fuel filter and clean it well, if it is clogged.
A fuel volume test will further confirm signs of a clogged filter. This test measures the volume of fuel delivered in a specified period of time. A fuel glow gauge is connected to fuel supply line, or the fuel return line is disconnected from fuel pressure regulator and the regulator is connected to a large container, in fuel volume test. This test aids in determining the amount of fuel which is flowing into the engine in the specified span of time. If the fuel volume is low, it indicates that the fuel filter has gone bad and needs to be replaced at the earliest.
Sometimes, foul odor of exhaust fumes also indicate a plugged fuel filter. But before you go about replacing the fuel filter, make sure that you relieve the fuel pressure prior to disconnecting the fuel lines from the filter (applicable for automobiles with high pressure system). And also check with the automobile manual and follow the specific instructions stated in it. Regular fuel filter maintenance is imperative to a good engine performance. If you are cleaning the fuel filter for the first time, it is advised that you do it under the supervision of an experienced mechanic.