TTEC4848 Vehicle Electronics Controls

"Fuel system blog"

How does fuel system works?

Although fuel systems vary from engine to engine, all systems are the same in the way that they must supply fuel to the combustion chamber and control the amount of fuel supplied in relation to the amount of air.

The fuel is stored in the fuel tank and the fuel pump draws the fuel from the tank. it then travels through a fuel filter to the fuel injectors. From here the fuel is already atomize and accomplished as a result of the injection pressure, also due to the diameter of the holes in the injector. Depending on whether the vehicle fuel system is a return type or return less type system, the fuel pressure based on the amount of vacuum from the intake system. This is so the amount of the fuel pressure flow of fuel as it reaches the injector remains consistently the same. On the other hand a return less type systems uses the power train control module (PCM) to regulate fuel delivery. There is a fuel pressure sensor mounted to the supply rail of the fuel injectors to allow the PCM monitor the pressure. When the fuel pressure and flow starts to drop due to increase of engine speed or load the PCM compensates by increasing the injector duration and/or operating the speed of the fuel pump.

Fuel tank

They material of a fuel tank can sometimes be made of stainless steel or durable plastic but are designed to be safe against flying rock and other road debris the tires may throw up at it. It's polished, pressurized and tested before it is able to provide the vehicle gas to get out of the factory.

When you fill your tank up with gasoline at the gas,the electric fuel pump (today's vehicles) begins to send a computer controlled amount of gas through the gas lines, that run the length of the undercarriage of your vehicle, to the gas regulator near the fuel injectors. The computer controls the amount of gas when you accelerate or decelerate, as well. The fuel pump sending unit sends information to the fuel gauge on the instrument panel on your dashboard, which gives you a heads-up if you are desperately in need of gas to get home.

Fuel tank Benefits

Storage: the system must contain a given quantity of fuel and must avoid leakage and limit evaporative emissions.

Filling: safe n no spark,

Provide a method for determining level of fuel in tank, gauging (the remaining quantity of fuel in the tank must be measured or evaluated).
Venting (if over-pressure is not allowed, the fuel vapors must be managed through valves).
Feeding of the engine (through a pump).
Anticipate potentials for damage and provide safe survival potential.

"How to test the fuel tank "

You can do various test to see if your fuel tank is working properly, if you car starts to waste a lot of petrol then you should take precaution and take a look at your vehicle.

Visual inspection = this can be done without the help of a certified person, your can do a fast visual inspection by just looking for any dripping of petrol or leaking on the fuel tank. Another very important element to inspect is the actual fuel cap, sometimes you might forget to put it back tight properly so there will be going a lot of air through and fuel vapors can escape and as a result your vehicle will be needing more fuel.

Fuel tank Bench test = this test should be performed with the fuel tank off the car or before putting it back on the vehicle. Testing the tank before installation should result in the discovery of defects in the tank that could result in drastic disassemble of the vehicle, if such test was performed after installation.

The tank should be empty for this test. Testing pressure can be supplied by pressurized air or compressed inert gas, different people have different ways of testing the fuel tank some use helium gas. Before making any test or compression test make sure of the tank’s rated testing pressure is marked on the tank. Personally i think this is the best way of testing your fuel tank, it is definitely accurate and efficient.

Fuel tank gauge

Helium testing or air compression

Fully seal fuel tank

Here is a video that explain how to find leaks on a fuel tank = http://youtu.be/ZfYgEhy7-bI

Here is another video looking at leakage

"Fuel pump"

There are three main types of fuel pumps that you will be able to find. Each has its own way of working its own qualities. It is important that you are able to know which one does what so that you will get the right one for you. That is why it is important to do your homework and shop around. It can be tricky to find the right one for you. Make sure you know if you will need a fuel pump that will pump the gas into a carburetor or into the fuel injection system. Know what the differences are and what they can accomplish for you.

Mechanical Fuel Pump

The mechanical fuel pump is one that is most often used with engines that use a carburetor. Back before fuel pumps became a necessity for cars, the fuel was fed directly into the carburetor. This was done through the act of gravity. They are on their way out as they pump fuel at very low pressure rates. Over time they are being used less and less, most exclusively in older cars. Pretty much any new or even newer car is not going to use this type of fuel pump. Eventually they will be completely phased out as newer cars do not require them at all. Because the mechanical fuel pump pumps the fuel into the carburetor, this slows down the efficiency of the fuel delivery. The fuel injection has become the more contemporary source with cars. The fuel is pumped at a higher pressure and will help to deliver the fuel in the most efficient way possible.

Checking the mechanical pump operation

The 'proper' way to test a pump is to put a pressure gauge on one side and a vacuum gauge on the other. A simpler way is shown here.

Do not test the pump by blowing compressed air into it: you may burst the diaphragm.

Even if you find the fault, you may not be able to mend it. If the pump is sealed, it will have to be replaced.

But if there is an obstruction under the filter (if any) you may be able to get at it by removing the filter (SeeCleaning fuel-pump filters).

When you take the pump off your vehicle, test it at once before the fuel in it dries up. Dry valves do not always seat fully.

If a car stops and has not run out of petrol, check whether there is petrol in the carburettor. If there is not, there is a fault in the fuel system.

Electrical Fuel pump

The high pressure pump can either be in-tank or external.

The fuel pump is basically an electric motor; fuel is drawn in from the inlet by

the roller cell or blades (depending on design) and expelled under high

pressure. Although sparks are generated by the brushes rubbing on the

commutator, an explosion cannot occur because the armature is completely

immersed in fuel (no air is available).

Fuel pumps are a sealed unit and must be replaced if they are worn out or

leak.

WARNING: DO NOT test a fuel pump dry or run low on fuel! (1/4 tank min.).

Fuel pumps are not designed to be run with no fuel for excessive time

periods.

This is the current wave form from a fuel pump

The wave form above will shows the current for each sector of the commutator. The

majority of fuel pumps have six to eight sectors and a repetitive point on the

waveform can indicate wear and an impending failure. It can be seen that

there is a lower current draw on one sector and this is repeated when the

armature has rotated through 720 deg. This fuel pump has eight sectors per

rotation. The current drawn is dependent on the fuel pressure and should not be more

than 8A.

How to bench test a fuel pump

A very simple way of testing a fuel pump is to hook up power from a batter to positive side and you can test, however not a good idea to run to long with no gasoline going through it.